xrt_compositor.h

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// Copyright 2019-2024, Collabora, Ltd.
// Copyright 2025, NVIDIA CORPORATION.
// SPDX-License-Identifier: BSL-1.0
/*!
 * @file
 * @brief  Header declaring XRT graphics interfaces.
 * @author Jakob Bornecrantz <jakob@collabora.com>
 * @author Lubosz Sarnecki <lubosz.sarnecki@collabora.com>
 * @author Rylie Pavlik <rylie.pavlik@collabora.com>
 * @author Christoph Haag <christoph.haag@collabora.com>
 * @author Korcan Hussein <korcan.hussein@collabora.com>
 * @ingroup xrt_iface
 */
 
#pragma once
 
#include "xrt/xrt_limits.h"
#include "xrt/xrt_defines.h"
#include "xrt/xrt_handles.h"
#include "xrt/xrt_config_os.h"
#include "xrt/xrt_config_have.h"
#include "xrt/xrt_windows.h"
 
#if defined(XRT_HAVE_D3D11)
#include <d3d11.h>
#elif defined(XRT_DOXYGEN)
struct ID3D11Texture2D;
#endif
 
#if defined(XRT_HAVE_D3D12)
#include <d3d12.h>
#elif defined(XRT_DOXYGEN)
struct ID3D12Resource;
#endif
 
#ifdef __cplusplus
extern "C" {
#endif
 
 
/*
 *
 * Pre-declare things, also they should not be in the xrt_iface group.
 *
 */
 
struct xrt_device;
struct xrt_image_native;
struct xrt_compositor;
struct xrt_session_event_sink;
 
typedef struct VkCommandBuffer_T *VkCommandBuffer;
#ifdef XRT_64_BIT
typedef struct VkImage_T *VkImage;
typedef struct VkDeviceMemory_T *VkDeviceMemory;
#else
typedef uint64_t VkImage;
typedef uint64_t VkDeviceMemory;
#endif
 
 
/*!
 * @addtogroup xrt_iface
 * @{
 */
 
 
/*
 *
 * Layers.
 *
 */
 
/*!
 * Layer type.
 */
enum xrt_layer_type
{
        XRT_LAYER_PROJECTION,
        XRT_LAYER_PROJECTION_DEPTH,
        XRT_LAYER_QUAD,
        XRT_LAYER_CUBE,
        XRT_LAYER_CYLINDER,
        XRT_LAYER_EQUIRECT1,
        XRT_LAYER_EQUIRECT2,
        XRT_LAYER_PASSTHROUGH
};
 
/*!
 * Bit field for holding information about how a layer should be composited.
 */
enum xrt_layer_composition_flags
{
        XRT_LAYER_COMPOSITION_CORRECT_CHROMATIC_ABERRATION_BIT = 1u << 0u,
        XRT_LAYER_COMPOSITION_BLEND_TEXTURE_SOURCE_ALPHA_BIT = 1u << 1u,
        XRT_LAYER_COMPOSITION_UNPREMULTIPLIED_ALPHA_BIT = 1u << 2u,
        /*!
         * The layer is locked to the device and the pose should only be
         * adjusted for the IPD.
         */
        XRT_LAYER_COMPOSITION_VIEW_SPACE_BIT = 1u << 3u,
 
        /*!
         * If this flag is set the compositor should use the scale and bias
         * from the @ref xrt_layer_data struct.
         */
        XRT_LAYER_COMPOSITION_COLOR_BIAS_SCALE = 1u << 4u,
 
        //! Normal super sampling, see XrCompositionLayerSettingsFlagsFB.
        XRT_COMPOSITION_LAYER_PROCESSING_NORMAL_SUPER_SAMPLING_BIT_FB = 1u << 5u,
 
        //! Quality super sampling, see XrCompositionLayerSettingsFlagsFB.
        XRT_COMPOSITION_LAYER_PROCESSING_QUALITY_SUPER_SAMPLING_BIT_FB = 1u << 6u,
 
        //! Normal sharpening, see XrCompositionLayerSettingsFlagsFB.
        XRT_COMPOSITION_LAYER_PROCESSING_NORMAL_SHARPENING_BIT_FB = 1u << 7u,
 
        //! Quality sharpening, see XrCompositionLayerSettingsFlagsFB.
        XRT_COMPOSITION_LAYER_PROCESSING_QUALITY_SHARPENING_BIT_FB = 1u << 8u,
 
        /*!
         * This layer has advanced blending information, this bit
         * supersedes the behavior of
         * @ref XRT_LAYER_COMPOSITION_BLEND_TEXTURE_SOURCE_ALPHA_BIT,
         * see @p XrCompositionLayerAlphaBlendFB.
         */
        XRT_LAYER_COMPOSITION_ADVANCED_BLENDING_BIT = 1u << 9u,
 
        /*!
         * Depth testing is requested when composing this layer if this flag is set,
         * see XrCompositionLayerDepthTestFB.
         */
        XRT_LAYER_COMPOSITION_DEPTH_TEST = 1u << 10u,
 
        /*!
         * This layer has inverted alpha,
         * see @p XR_COMPOSITION_LAYER_INVERTED_ALPHA_BIT_EXT
         */
        XRT_LAYER_COMPOSITION_INVERTED_ALPHA_BIT = 1u << 11u,
 
        /*!
         * When "emulating" a quad view projection layer with two stereo
         * projection layers this is used to tag the context (background) layer
         * that the inset layer is blended with.
         */
        XRT_LAYER_SPLIT_QUAD_VIEW_CONTEXT = 1u << 12u,
 
        /*!
         * When "emulating" a quad view projection layer with two stereo
         * projection layers this is used to tag the inset layer so that the
         * compositor can apply blending between the two. Essentially this tells
         * the compositor to blend the edges of this layer with the context
         * layer below it.
         */
        XRT_LAYER_SPLIT_QUAD_VIEW_INSET = 1u << 13u,
};
 
/*!
 * XrCompareOpFB
 */
enum xrt_compare_op_fb
{
        XRT_COMPARE_OP_NEVER_FB = 0,
        XRT_COMPARE_OP_LESS_FB = 1,
        XRT_COMPARE_OP_EQUAL_FB = 2,
        XRT_COMPARE_OP_LESS_OR_EQUAL_FB = 3,
        XRT_COMPARE_OP_GREATER_FB = 4,
        XRT_COMPARE_OP_NOT_EQUAL_FB = 5,
        XRT_COMPARE_OP_GREATER_OR_EQUAL_FB = 6,
        XRT_COMPARE_OP_ALWAYS_FB = 7,
        XRT_COMPARE_OP_MAX_ENUM_FB = 0x7FFFFFFF
};
 
/*!
 * Which view is the layer visible to?
 *
 * Used for quad layers.
 *
 * @note Doesn't have the same values as the OpenXR counterpart!
 */
enum xrt_layer_eye_visibility
{
        XRT_LAYER_EYE_VISIBILITY_NONE = 0x0,
        XRT_LAYER_EYE_VISIBILITY_LEFT_BIT = 0x1,
        XRT_LAYER_EYE_VISIBILITY_RIGHT_BIT = 0x2,
        XRT_LAYER_EYE_VISIBILITY_BOTH = 0x3,
};
 
/*!
 * Blend factors.
 */
enum xrt_blend_factor
{
        XRT_BLEND_FACTOR_ZERO = 0,
        XRT_BLEND_FACTOR_ONE = 1,
        XRT_BLEND_FACTOR_SRC_ALPHA = 2,
        XRT_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA = 3,
        XRT_BLEND_FACTOR_DST_ALPHA = 4,
        XRT_BLEND_FACTOR_ONE_MINUS_DST_ALPHA = 5,
        XRT_BLEND_FACTOR_MAX_ENUM_FB = 0x7FFFFFFF,
};
 
 
/*!
 * Chroma key parameters in HSV space.
 * Alpha 0-1 interpolates between hsv_min and hsv_max
 * with curve as a power curve defined by the curve exponent.
 *
 * Used for projection layers.
 */
struct xrt_layer_chroma_key_data
{
        //!< Minimum HSV bounds
        struct xrt_colour_hsv_f32 hsv_min;
        //! Maximum HSV bounds
        struct xrt_colour_hsv_f32 hsv_max;
        //! Power curve for alpha falloff (1.0 = linear)
        float curve;
        //! Despill strength (0.0 = none, 1.0 = full)
        float despill;
};
 
/*!
 * Advanced blend
 * provides explicit control over source and destination blend factors,
 * with separate controls for color and alpha
 *
 * See @ref XRT_LAYER_COMPOSITION_ADVANCED_BLENDING_BIT.
 */
struct xrt_layer_advanced_blend_data
{
        enum xrt_blend_factor src_factor_color;
        enum xrt_blend_factor dst_factor_color;
        enum xrt_blend_factor src_factor_alpha;
        enum xrt_blend_factor dst_factor_alpha;
};
 
/*!
 * Specifies a sub-image in a layer.
 */
struct xrt_sub_image
{
        //! Image index in the (implicit) swapchain
        uint32_t image_index;
        //! Index in image array (for array textures)
        uint32_t array_index;
        //! The rectangle in the image to use
        struct xrt_rect rect;
        //! Normalized sub image coordinates and size.
        struct xrt_normalized_rect norm_rect;
};
 
/*!
 * All of the pure data values associated with a single view in a projection
 * layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_projection_view_data
{
        struct xrt_sub_image sub;
 
        struct xrt_fov fov;
        struct xrt_pose pose;
};
 
/*!
 * All the pure data values associated with a projection layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_projection_data
{
        struct xrt_layer_projection_view_data v[XRT_MAX_VIEWS];
 
        struct xrt_layer_chroma_key_data chroma_key;
};
 
/*!
 * All the pure data values associated with a depth information attached
 * to a layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_depth_data
{
        struct xrt_sub_image sub;
 
        float min_depth;
        float max_depth;
        float near_z;
        float far_z;
};
 
struct xrt_layer_depth_test_data
{
        bool depth_mask;
        enum xrt_compare_op_fb compare_op;
};
 
/*!
 * All the pure data values associated with a projection layer with depth
 * swapchain attached.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_projection_depth_data
{
        struct xrt_layer_projection_view_data v[XRT_MAX_VIEWS];
 
        struct xrt_layer_depth_data d[XRT_MAX_VIEWS];
 
        struct xrt_layer_chroma_key_data chroma_key;
};
 
/*!
 * All the pure data values associated with a quad layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_quad_data
{
        enum xrt_layer_eye_visibility visibility;
 
        struct xrt_sub_image sub;
 
        struct xrt_pose pose;
        struct xrt_vec2 size;
};
 
/*!
 * All the pure data values associated with a cube layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_cube_data
{
        enum xrt_layer_eye_visibility visibility;
 
        struct xrt_sub_image sub;
 
        struct xrt_pose pose;
};
 
/*!
 * All the pure data values associated with a cylinder layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_cylinder_data
{
        enum xrt_layer_eye_visibility visibility;
 
        struct xrt_sub_image sub;
 
        struct xrt_pose pose;
        float radius;
        float central_angle;
        float aspect_ratio;
};
 
/*!
 * All the pure data values associated with a equirect1 layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_equirect1_data
{
        enum xrt_layer_eye_visibility visibility;
 
        struct xrt_sub_image sub;
 
        struct xrt_pose pose;
        float radius;
        struct xrt_vec2 scale;
        struct xrt_vec2 bias;
};
 
/*!
 * All the pure data values associated with a equirect2 layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_equirect2_data
{
        enum xrt_layer_eye_visibility visibility;
 
        struct xrt_sub_image sub;
 
        struct xrt_pose pose;
        float radius;
        float central_horizontal_angle;
        float upper_vertical_angle;
        float lower_vertical_angle;
};
 
/*!
 * @interface xrt_passthrough
 */
struct xrt_passthrough
{
        bool paused;
};
 
/*!
 * @interface xrt_passthrough_layer
 */
struct xrt_passthrough_layer
{
        bool paused;
};
 
/*!
 * All the pure data values associated with a passthrough layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_passthrough_data
{
        struct xrt_passthrough xrt_pt;
        struct xrt_passthrough_layer xrt_pl;
};
 
/*!
 * All the pure data values associated with a composition layer.
 *
 * The @ref xrt_swapchain references and @ref xrt_device are provided outside of
 * this struct.
 */
struct xrt_layer_data
{
        /*!
         * Tag for compositor layer type.
         */
        enum xrt_layer_type type;
 
        /*!
         * Often @ref XRT_INPUT_GENERIC_HEAD_POSE
         */
        enum xrt_input_name name;
 
        /*!
         * "Display no-earlier-than" timestamp for this layer.
         *
         * The layer may be displayed after this point, but must never be
         * displayed before.
         *
         * alignas for 32 bit client support,
         */
        XRT_ALIGNAS(8) int64_t timestamp;
 
        /*!
         * Composition flags
         */
        enum xrt_layer_composition_flags flags;
 
        /*!
         * Depth test data
         */
        struct xrt_layer_depth_test_data depth_test;
 
        /*!
         * Whether the main compositor should flip the direction of y when
         * rendering.
         *
         * This is actually an input only to the "main" compositor
         * comp_compositor. It is overwritten by the various client
         * implementations of the @ref xrt_compositor interface depending on the
         * conventions of the associated graphics API. Other @ref
         * xrt_compositor_native implementations that are not the main
         * compositor just pass this field along unchanged to the "real"
         * compositor.
         */
        bool flip_y;
 
        /*!
         * Modulate the color sourced from the images.
         */
        struct xrt_colour_rgba_f32 color_scale;
 
        /*!
         * Modulate the color sourced from the images.
         */
        struct xrt_colour_rgba_f32 color_bias;
 
        /*!
         * Advanced blend factors
         */
        struct xrt_layer_advanced_blend_data advanced_blend;
 
        /*!
         * Union of data values for the various layer types.
         *
         * The initialized member of this union should match the value of
         * xrt_layer_data::type. It also should be clear because of the layer
         * function called between xrt_compositor::layer_begin and
         * xrt_compositor::layer_commit where this data was passed.
         */
        union {
                struct xrt_layer_projection_data proj;
                struct xrt_layer_projection_depth_data depth;
                struct xrt_layer_quad_data quad;
                struct xrt_layer_cube_data cube;
                struct xrt_layer_cylinder_data cylinder;
                struct xrt_layer_equirect1_data equirect1;
                struct xrt_layer_equirect2_data equirect2;
                struct xrt_layer_passthrough_data passthrough;
        };
        uint32_t view_count;
};
 
/*!
 * Per frame data for the layer submission calls, used in
 * @ref xrt_compositor::layer_begin.
 */
struct xrt_layer_frame_data
{
        //! alignas for 32 bit client support, see @ref ipc-design
        XRT_ALIGNAS(8) int64_t frame_id;
        int64_t display_time_ns;
        enum xrt_blend_mode env_blend_mode;
};
 
 
/*
 *
 * Swapchain.
 *
 */
 
/*!
 * @interface xrt_swapchain
 *
 * Common swapchain interface/base.
 *
 * Swapchains are owned by the @ref xrt_compositor that they where created from,
 * it's the state trackers job to ensure all swapchains are destroyed before
 * destroying the @ref xrt_compositor.
 */
struct xrt_swapchain
{
        /*!
         * Reference helper.
         */
        struct xrt_reference reference;
 
        /*!
         * Number of images.
         *
         * The images themselves are on the subclasses.
         */
        uint32_t image_count;
 
        /*!
         * @ref dec_image_use must have been called as often as @ref inc_image_use.
         */
        void (*destroy)(struct xrt_swapchain *xsc);
 
        /*!
         * Obtain the index of the next image to use, without blocking on being
         * able to write to it.
         *
         * See xrAcquireSwapchainImage.
         *
         * Caller must make sure that no image is acquired before calling
         * @ref xrt_swapchain_acquire_image.
         *
         * @param xsc Self pointer
         * @param[out] out_index Image index to use next
         *
         * Call @ref xrt_swapchain_wait_image before writing to the image index output from this function.
         */
        xrt_result_t (*acquire_image)(struct xrt_swapchain *xsc, uint32_t *out_index);
 
        /*!
         * @brief Increments the use counter of a swapchain image.
         */
        xrt_result_t (*inc_image_use)(struct xrt_swapchain *xsc, uint32_t index);
 
        /*!
         * @brief Decrements the use counter of a swapchain image.
         *
         * @ref wait_image will return once the image use counter is 0.
         */
        xrt_result_t (*dec_image_use)(struct xrt_swapchain *xsc, uint32_t index);
 
        /*!
         * Wait until image @p index is available for exclusive use, or until @p timeout_ns expires.
         *
         * See xrWaitSwapchainImage, which is the basis for this API.
         * The state tracker needs to track image index, which should have come from @ref xrt_swapchain_acquire_image
 
         * @param xsc Self pointer
         * @param timeout_ns Timeout in nanoseconds,
         * @param index Image index to wait for.
         */
        xrt_result_t (*wait_image)(struct xrt_swapchain *xsc, int64_t timeout_ns, uint32_t index);
 
        /*!
         * Do any barrier transitions to and from the application.
         *
         * @param xsc       Self pointer
         * @param direction Direction of the barrier transition.
         * @param index     Image index to barrier transition.
         */
        xrt_result_t (*barrier_image)(struct xrt_swapchain *xsc, enum xrt_barrier_direction direction, uint32_t index);
 
        /*!
         * See xrReleaseSwapchainImage, state tracker needs to track index.
         */
        xrt_result_t (*release_image)(struct xrt_swapchain *xsc, uint32_t index);
};
 
/*!
 * Update the reference counts on swapchain(s).
 *
 * @param[in,out] dst Pointer to a object reference: if the object reference is
 *                non-null will decrement its counter. The reference that
 *                @p dst points to will be set to @p src.
 * @param[in] src New object for @p dst to refer to (may be null).
 *                If non-null, will have its refcount increased.
 * @ingroup xrt_iface
 * @relates xrt_swapchain
 */
XRT_NONNULL_FIRST static inline void
xrt_swapchain_reference(struct xrt_swapchain **dst, struct xrt_swapchain *src)
{
        struct xrt_swapchain *old_dst = *dst;
 
        if (old_dst == src) {
                return;
        }
 
        if (src) {
                xrt_reference_inc(&src->reference);
        }
 
        *dst = src;
 
        if (old_dst) {
                if (xrt_reference_dec_and_is_zero(&old_dst->reference)) {
                        old_dst->destroy(old_dst);
                }
        }
}
 
/*!
 * @copydoc xrt_swapchain::acquire_image
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_acquire_image(struct xrt_swapchain *xsc, uint32_t *out_index)
{
        return xsc->acquire_image(xsc, out_index);
}
 
/*!
 * @copydoc xrt_swapchain::inc_image_use
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_inc_image_use(struct xrt_swapchain *xsc, uint32_t index)
{
        return xsc->inc_image_use(xsc, index);
}
 
/*!
 * @copydoc xrt_swapchain::dec_image_use
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_dec_image_use(struct xrt_swapchain *xsc, uint32_t index)
{
        return xsc->dec_image_use(xsc, index);
}
 
/*!
 * @copydoc xrt_swapchain::wait_image
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_wait_image(struct xrt_swapchain *xsc, int64_t timeout_ns, uint32_t index)
{
        return xsc->wait_image(xsc, timeout_ns, index);
}
 
/*!
 * @copydoc xrt_swapchain::barrier_image
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_barrier_image(struct xrt_swapchain *xsc, enum xrt_barrier_direction direction, uint32_t index)
{
        return xsc->barrier_image(xsc, direction, index);
}
 
/*!
 * @copydoc xrt_swapchain::release_image
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_swapchain
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_swapchain_release_image(struct xrt_swapchain *xsc, uint32_t index)
{
        return xsc->release_image(xsc, index);
}
 
 
/*
 *
 * Fence.
 *
 */
 
/*!
 * Compositor fence used for synchronization.
 */
struct xrt_compositor_fence
{
        /*!
         * Waits on the fence with the given timeout.
         */
        xrt_result_t (*wait)(struct xrt_compositor_fence *xcf, uint64_t timeout);
 
        /*!
         * Destroys the fence.
         */
        void (*destroy)(struct xrt_compositor_fence *xcf);
};
 
/*!
 * @copydoc xrt_compositor_fence::wait
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor_fence
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_compositor_fence_wait(struct xrt_compositor_fence *xcf, uint64_t timeout)
{
        return xcf->wait(xcf, timeout);
}
 
/*!
 * @copydoc xrt_compositor_fence::destroy
 *
 * Helper for calling through the function pointer: does a null check and sets
 * xcf_ptr to null if freed.
 *
 * @public @memberof xrt_compositor_fence
 */
static inline void
xrt_compositor_fence_destroy(struct xrt_compositor_fence **xcf_ptr)
{
        struct xrt_compositor_fence *xcf = *xcf_ptr;
        if (xcf == NULL) {
                return;
        }
 
        xcf->destroy(xcf);
        *xcf_ptr = NULL;
}
 
 
/*
 *
 * Compositor semaphore.
 *
 */
 
/*!
 * Compositor semaphore used for synchronization, needs to be as capable as a
 * Vulkan pipeline semaphore.
 */
struct xrt_compositor_semaphore
{
        /*!
         * Reference helper.
         */
        struct xrt_reference reference;
 
        /*!
         * Does a CPU side wait on the semaphore to reach the given value.
         */
        xrt_result_t (*wait)(struct xrt_compositor_semaphore *xcsem, uint64_t value, uint64_t timeout_ns);
 
        /*!
         * Destroys the semaphore.
         */
        void (*destroy)(struct xrt_compositor_semaphore *xcsem);
};
 
/*!
 * Update the reference counts on compositor semaphore(s).
 *
 * @param[in,out] dst Pointer to a object reference: if the object reference is
 *                non-null will decrement its counter. The reference that
 *                @p dst points to will be set to @p src.
 * @param[in] src New object for @p dst to refer to (may be null).
 *                If non-null, will have its refcount increased.
 * @ingroup xrt_iface
 * @relates xrt_compositor_semaphore
 */
XRT_NONNULL_FIRST static inline void
xrt_compositor_semaphore_reference(struct xrt_compositor_semaphore **dst, struct xrt_compositor_semaphore *src)
{
        struct xrt_compositor_semaphore *old_dst = *dst;
 
        if (old_dst == src) {
                return;
        }
 
        if (src) {
                xrt_reference_inc(&src->reference);
        }
 
        *dst = src;
 
        if (old_dst) {
                if (xrt_reference_dec_and_is_zero(&old_dst->reference)) {
                        old_dst->destroy(old_dst);
                }
        }
}
 
/*!
 * @copydoc xrt_compositor_semaphore::wait
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor_semaphore
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_compositor_semaphore_wait(struct xrt_compositor_semaphore *xcsem, uint64_t value, uint64_t timeout)
{
        return xcsem->wait(xcsem, value, timeout);
}
 
 
/*
 *
 * Compositor.
 *
 */
 
enum xrt_compositor_frame_point
{
        XRT_COMPOSITOR_FRAME_POINT_WOKE, //!< The client woke up after waiting.
};
 
/*!
 * Swapchain creation info.
 */
struct xrt_swapchain_create_info
{
        enum xrt_swapchain_create_flags create;
        enum xrt_swapchain_usage_bits bits;
        uint32_t format;
        uint32_t sample_count;
        uint32_t width;
        uint32_t height;
        uint32_t face_count;
        uint32_t array_size;
        uint32_t mip_count;
 
        /*
         * List of formats that could be used when creating views of the swapchain images.
         * See XR_KHR_vulkan_swapchain_format_list and VK_KHR_image_format_list
         */
        uint32_t format_count;
        uint32_t formats[XRT_MAX_SWAPCHAIN_CREATE_INFO_FORMAT_LIST_COUNT];
};
 
/*!
 * Passthrough creation info.
 */
struct xrt_passthrough_create_info
{
        enum xrt_passthrough_create_flags create;
};
 
/*!
 * Passthrough layer creation info.
 */
struct xrt_passthrough_layer_create_info
{
        enum xrt_passthrough_create_flags create;
        enum xrt_passthrough_purpose_flags purpose;
};
 
/*!
 * Struct used to negotiate properties of a swapchain that is created outside
 * of the compositor. Often used by a client compositor or IPC layer to allocate
 * the swapchain images and then pass them into the native compositor.
 */
struct xrt_swapchain_create_properties
{
        //! How many images the compositor want in the swapchain.
        uint32_t image_count;
 
        //! New creation bits.
        enum xrt_swapchain_usage_bits extra_bits;
};
 
/*!
 * Session information, mostly overlay extension data.
 */
struct xrt_session_info
{
        bool is_overlay;
        //! alignas for 32 bit client support, see @ref ipc-design
        XRT_ALIGNAS(8) uint64_t flags;
        uint32_t z_order;
};
 
/*!
 * Capabilities and information about the compositor and device together.
 *
 * For client compositors the formats of the native compositor are translated.
 */
struct xrt_compositor_info
{
        //! Number of formats, never changes.
        uint32_t format_count;
 
        /*!
         * Supported formats, never changes.
         * alignas for 32 bit client support, see @ref ipc-design
         */
        XRT_ALIGNAS(8) int64_t formats[XRT_MAX_SWAPCHAIN_FORMATS];
 
        //! Max texture size that GPU supports (size of a single dimension), zero means any size.
        uint32_t max_texture_size;
};
 
/*!
 * Begin Session information not known until clients have created an xrt-instance such as which
 * extensions are enabled, view type, etc.
 */
struct xrt_begin_session_info
{
        enum xrt_view_type view_type;
        bool ext_hand_tracking_enabled;
        bool ext_hand_tracking_data_source_enabled;
        bool ext_eye_gaze_interaction_enabled;
        bool ext_future_enabled;
        bool ext_hand_interaction_enabled;
        bool htc_facial_tracking_enabled;
        bool fb_body_tracking_enabled;
        bool fb_face_tracking2_enabled;
        bool meta_body_tracking_full_body_enabled;
        bool meta_body_tracking_calibration_enabled;
        bool meta_body_tracking_fidelity_enabled;
        bool android_face_tracking_enabled;
};
 
/*!
 * Hints the XR runtime what type of task the thread is doing.
 */
enum xrt_thread_hint
{
        XRT_THREAD_HINT_APPLICATION_MAIN = 1,
        XRT_THREAD_HINT_APPLICATION_WORKER = 2,
        XRT_THREAD_HINT_RENDERER_MAIN = 3,
        XRT_THREAD_HINT_RENDERER_WORKER = 4,
};
 
/*!
 * @interface xrt_compositor
 *
 * Common compositor client interface/base.
 *
 * A compositor is very much analogous to an `XrSession` but without any of the
 * input functionality, and does have the same lifetime as an `XrSession`.
 */
struct xrt_compositor
{
        /*!
         * Capabilities and recommended values information.
         */
        struct xrt_compositor_info info;
 
        /*!
         * For a given @ref xrt_swapchain_create_info struct returns a filled
         * out @ref xrt_swapchain_create_properties.
         */
        xrt_result_t (*get_swapchain_create_properties)(struct xrt_compositor *xc,
                                                        const struct xrt_swapchain_create_info *info,
                                                        struct xrt_swapchain_create_properties *xsccp);
 
        /*!
         * @name Function pointers for swapchain and sync creation and import
         * @{
         */
        /*!
         * Create a swapchain with a set of images.
         *
         * The pointer pointed to by @p out_xsc has to either be NULL or a valid
         * @ref xrt_swapchain pointer. If there is a valid @ref xrt_swapchain
         * pointed by the pointed pointer it will have it reference decremented.
         */
        xrt_result_t (*create_swapchain)(struct xrt_compositor *xc,
                                         const struct xrt_swapchain_create_info *info,
                                         struct xrt_swapchain **out_xsc);
 
        /*!
         * Create a swapchain from a set of native images.
         *
         * The pointer pointed to by @p out_xsc has to either be NULL or a valid
         * @ref xrt_swapchain pointer. If there is a valid @ref xrt_swapchain
         * pointed by the pointed pointer it will have it reference decremented.
         */
        xrt_result_t (*import_swapchain)(struct xrt_compositor *xc,
                                         const struct xrt_swapchain_create_info *info,
                                         struct xrt_image_native *native_images,
                                         uint32_t image_count,
                                         struct xrt_swapchain **out_xsc);
 
        /*!
         * Create a compositor fence from a native sync handle.
         */
        xrt_result_t (*import_fence)(struct xrt_compositor *xc,
                                     xrt_graphics_sync_handle_t handle,
                                     struct xrt_compositor_fence **out_xcf);
 
        /*!
         * Create a compositor semaphore, also returns a native handle of the
         * semaphore which is owned by the @ref xrt_compositor_semaphore struct.
         * The return values are always both valid, or on an error condition
         * encountered and error is returned, both not valid (untouched).
         *
         * @param[in]  xc         Compositor self pointer.
         * @param[out] out_handle Native handle owned by the samephore.
         * @param[out] out_handle Return of the created semahpore.
         */
        xrt_result_t (*create_semaphore)(struct xrt_compositor *xc,
                                         xrt_graphics_sync_handle_t *out_handle,
                                         struct xrt_compositor_semaphore **out_xcsem);
        /*! @} */
 
        /*!
         * Create a passthrough.
         */
        xrt_result_t (*create_passthrough)(struct xrt_compositor *xc, const struct xrt_passthrough_create_info *info);
 
 
        /*!
         * Create a passthrough layer.
         */
        xrt_result_t (*create_passthrough_layer)(struct xrt_compositor *xc,
                                                 const struct xrt_passthrough_layer_create_info *info);
        /*!
         * Destroy a passthrough.
         */
        xrt_result_t (*destroy_passthrough)(struct xrt_compositor *xc);
 
        /*!
         * @name Function pointers for session functions
         * @{
         */
        /*!
         * See xrBeginSession.
         */
        xrt_result_t (*begin_session)(struct xrt_compositor *xc, const struct xrt_begin_session_info *info);
 
        /*!
         * See xrEndSession, unlike the OpenXR one the state tracker is
         * responsible to call discard frame before calling this function. See
         * discard_frame.
         */
        xrt_result_t (*end_session)(struct xrt_compositor *xc);
 
        /*! @} */
 
        /*!
         * @name Function pointers for frame functions
         * @{
         */
 
        /*!
         * This function and @ref mark_frame function calls are a alternative to
         * @ref wait_frame.
         *
         * The only requirement on the compositor for the @p frame_id
         * is that it is a positive number and larger then the last returned
         * frame_id.
         *
         * After a call to predict_frame, the state tracker is not allowed to
         * call this function until after a call to @ref mark_frame (with point
         * @ref XRT_COMPOSITOR_FRAME_POINT_WOKE), followed by either
         * @ref begin_frame or @ref discard_frame.
         *
         * @param[in]  xc                              The compositor
         * @param[out] out_frame_id                    Frame id
         * @param[out] out_wake_time_ns                When we want the client to be awoken to begin rendering.
         * @param[out] out_predicted_gpu_time_ns       When we expect the client to finish the GPU work. If not
         *                                             computed/available, set to 0.
         * @param[out] out_predicted_display_time_ns   When the pixels turns into photons.
         * @param[out] out_predicted_display_period_ns The period for the frames.
         */
        xrt_result_t (*predict_frame)(struct xrt_compositor *xc,
                                      int64_t *out_frame_id,
                                      int64_t *out_wake_time_ns,
                                      int64_t *out_predicted_gpu_time_ns,
                                      int64_t *out_predicted_display_time_ns,
                                      int64_t *out_predicted_display_period_ns);
 
        /*!
         * This function and @ref predict_frame function calls are a alternative to
         * @ref wait_frame.
         *
         * If point is @ref XRT_COMPOSITOR_FRAME_POINT_WOKE it is to mark that the
         * client woke up from waiting on a frame.
         *
         * @param[in] xc       The compositor
         * @param[in] frame_id Frame id
         * @param[in] point    What type of frame point to mark.
         * @param[in] when_ns  When this point happened.
         */
        xrt_result_t (*mark_frame)(struct xrt_compositor *xc,
                                   int64_t frame_id,
                                   enum xrt_compositor_frame_point point,
                                   int64_t when_ns);
 
        /*!
         * See xrWaitFrame.
         *
         * This function has the same semantics as calling @ref predict_frame,
         * sleeping, and then calling @ref mark_frame with a point of
         * @ref XRT_COMPOSITOR_FRAME_POINT_WOKE.
         *
         * The only requirement on the compositor for the @p frame_id
         * is that it is a positive number and larger then the last returned
         * @p frame_id.
         *
         * After a call to wait_frame, the state tracker is not allowed to call
         * this function until after a call to either @ref begin_frame or
         * @ref discard_frame.
         *
         * If the caller can do its own blocking, use the pair of functions
         * xrt_compositor::predict_frame and xrt_compositor::mark_frame instead
         * of this single blocking function.
         */
        xrt_result_t (*wait_frame)(struct xrt_compositor *xc,
                                   int64_t *out_frame_id,
                                   int64_t *out_predicted_display_time,
                                   int64_t *out_predicted_display_period);
 
        /*!
         * See xrBeginFrame.
         *
         * Must have made a call to either @ref predict_frame or @ref wait_frame
         * before calling this function. After this function is called you must
         * call layer_commit.
         *
         * @param[in] xc       The compositor
         * @param[in] frame_id Frame id
         */
        xrt_result_t (*begin_frame)(struct xrt_compositor *xc, int64_t frame_id);
 
        /*!
         * @brief Explicitly discard a frame.
         *
         * This isn't in the OpenXR API but is explicit in the XRT interfaces.
         *
         * Two calls to xrBeginFrame without intervening xrEndFrame will cause
         * the state tracker to call:
         *
         * ```c
         * // first xrBeginFrame
         * xrt_comp_begin_frame(xc, frame_id);
         * // second xrBeginFrame
         * xrt_comp_discard_frame(xc, frame_id);
         * xrt_comp_begin_frame(xc, frame_id);
         * ```
         */
        xrt_result_t (*discard_frame)(struct xrt_compositor *xc, int64_t frame_id);
 
        /*! @} */
 
 
        /*!
         * @name Function pointers for layer submission
         * @{
         */
        /*!
         * @brief Begins layer submission.
         *
         * This and the other `layer_*` calls are equivalent to xrEndFrame,
         * except split over multiple calls. It's only after
         * xrt_compositor::layer_commit that layers will be displayed.
         * From the point of view of the swapchain, the image is used as
         * soon as it's given in a call.
         */
        xrt_result_t (*layer_begin)(struct xrt_compositor *xc, const struct xrt_layer_frame_data *data);
 
        /*!
         * @brief Adds a projection layer for submissions.
         *
         * Note that e.g. the same swapchain object may be passed as both
         * @p l_xsc and @p r_xsc - the parameters in @p data identify
         * the subrect and array texture index to use for each of the views.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Array of swapchain objects containing eye RGB data.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what parts of the supplied swapchain
         *                    objects to use for each view.
         */
        xrt_result_t (*layer_projection)(struct xrt_compositor *xc,
                                         struct xrt_device *xdev,
                                         struct xrt_swapchain *xsc[XRT_MAX_VIEWS],
                                         const struct xrt_layer_data *data);
 
        /*!
         * @brief Adds a projection layer for submission, has depth information.
         *
         * Note that e.g. the same swapchain object may be passed as both
         * @p l_xsc and @p r_xsc - the parameters in @p data identify
         * the subrect and array texture index to use for each of the views.
         * This flexibility is required by the OpenXR API and is passed through
         * to the compositor to preserve the maximum information
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Array of swapchain objects containing eye RGB data.
         * @param d_xsc       Array of swapchain objects containing eye depth data.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what parts of the supplied swapchain
         *                    objects to use for each view.
         */
        xrt_result_t (*layer_projection_depth)(struct xrt_compositor *xc,
                                               struct xrt_device *xdev,
                                               struct xrt_swapchain *xsc[XRT_MAX_VIEWS],
                                               struct xrt_swapchain *d_xsc[XRT_MAX_VIEWS],
                                               const struct xrt_layer_data *data);
 
        /*!
         * Adds a quad layer for submission, the center of the quad is specified
         * by the pose and extends outwards from it.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Swapchain.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_quad)(struct xrt_compositor *xc,
                                   struct xrt_device *xdev,
                                   struct xrt_swapchain *xsc,
                                   const struct xrt_layer_data *data);
 
        /*!
         * Adds a cube layer for submission.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Swapchain.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_cube)(struct xrt_compositor *xc,
                                   struct xrt_device *xdev,
                                   struct xrt_swapchain *xsc,
                                   const struct xrt_layer_data *data);
 
        /*!
         * Adds a cylinder layer for submission.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Swapchain.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_cylinder)(struct xrt_compositor *xc,
                                       struct xrt_device *xdev,
                                       struct xrt_swapchain *xsc,
                                       const struct xrt_layer_data *data);
 
        /*!
         * Adds a equirect1 layer for submission.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Swapchain.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_equirect1)(struct xrt_compositor *xc,
                                        struct xrt_device *xdev,
                                        struct xrt_swapchain *xsc,
                                        const struct xrt_layer_data *data);
 
 
        /*!
         * Adds a equirect2 layer for submission.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param xsc         Swapchain.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_equirect2)(struct xrt_compositor *xc,
                                        struct xrt_device *xdev,
                                        struct xrt_swapchain *xsc,
                                        const struct xrt_layer_data *data);
 
        /*!
         * Adds a passthrough layer for submission.
         *
         * @param xc          Self pointer
         * @param xdev        The device the layer is relative to.
         * @param data        All of the pure data bits (not pointers/handles),
         *                    including what part of the supplied swapchain
         *                    object to use.
         */
        xrt_result_t (*layer_passthrough)(struct xrt_compositor *xc,
                                          struct xrt_device *xdev,
                                          const struct xrt_layer_data *data);
 
        /*!
         * @brief Commits all of the submitted layers.
         *
         * Only after this call will the compositor actually use the layers.
         */
        xrt_result_t (*layer_commit)(struct xrt_compositor *xc, xrt_graphics_sync_handle_t sync_handle);
 
        /*!
         * @brief Commits all of the submitted layers, with a semaphore.
         *
         * Only after this call will the compositor actually use the layers.
         * @param xc          Self pointer
         * @param xcsem       Semaphore that will be signalled when the app GPU
         *                    work has completed.
         * @param value       Semaphore value upone completion of GPU work.
         */
        xrt_result_t (*layer_commit_with_semaphore)(struct xrt_compositor *xc,
                                                    struct xrt_compositor_semaphore *xcsem,
                                                    uint64_t value);
 
        /*! @} */
 
 
        /*!
         * @name Function pointers for XR_FB_display_refresh_rate.
         * @{
         */
 
        /*!
         * Get the current display refresh rate.
         *
         * @param xc                                        Self pointer
         * @param out_display_refresh_rate_hz   Current display refresh rate in Hertz.
         */
        xrt_result_t (*get_display_refresh_rate)(struct xrt_compositor *xc, float *out_display_refresh_rate_hz);
 
        /*!
         * Request system to change the display refresh rate to the requested value.
         *
         * @param xc                                 Self pointer
         * @param display_refresh_rate_hz    Requested display refresh rate in Hertz.
         */
        xrt_result_t (*request_display_refresh_rate)(struct xrt_compositor *xc, float display_refresh_rate_hz);
 
        /*! @} */
 
 
        /*!
         * @brief Set CPU/GPU performance level.
         */
        xrt_result_t (*set_performance_level)(struct xrt_compositor *xc,
                                              enum xrt_perf_domain domain,
                                              enum xrt_perf_set_level level);
 
        /*!
         * @brief Get the extents of the reference space's bounds rectangle.
         */
        xrt_result_t (*get_reference_bounds_rect)(struct xrt_compositor *xc,
                                                  enum xrt_reference_space_type reference_space_type,
                                                  struct xrt_vec2 *bounds);
 
        /*!
         * Teardown the compositor.
         *
         * The state tracker must have made sure that no frames or sessions are
         * currently pending.
         *
         * @see xrt_compositor::discard_frame or xrt_compositor::end_frame for a pending frame
         * @see xrt_compositor::end_session for an open session.
         */
        void (*destroy)(struct xrt_compositor *xc);
 
        /*!
         * @name Function pointers for extensions
         * @{
         */
 
        /*!
         * @brief Set thread attributes according to thread type
         */
        xrt_result_t (*set_thread_hint)(struct xrt_compositor *xc, enum xrt_thread_hint hint, uint32_t thread_id);
 
        /*! @} */
};
 
/*!
 * @copydoc xrt_compositor::get_swapchain_create_properties
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_get_swapchain_create_properties(struct xrt_compositor *xc,
                                         const struct xrt_swapchain_create_info *info,
                                         struct xrt_swapchain_create_properties *xsccp)
{
        return xc->get_swapchain_create_properties(xc, info, xsccp);
}
 
/*!
 * @name Swapchain and sync creation and import methods
 * @{
 */
 
/*!
 * @copydoc xrt_compositor::create_swapchain
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_create_swapchain(struct xrt_compositor *xc,
                          const struct xrt_swapchain_create_info *info,
                          struct xrt_swapchain **out_xsc)
{
        return xc->create_swapchain(xc, info, out_xsc);
}
 
/*!
 * @copydoc xrt_compositor::import_swapchain
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_import_swapchain(struct xrt_compositor *xc,
                          const struct xrt_swapchain_create_info *info,
                          struct xrt_image_native *native_images,
                          uint32_t image_count,
                          struct xrt_swapchain **out_xsc)
{
        return xc->import_swapchain(xc, info, native_images, image_count, out_xsc);
}
 
/*!
 * @copydoc xrt_compositor::import_fence
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_import_fence(struct xrt_compositor *xc,
                      xrt_graphics_sync_handle_t handle,
                      struct xrt_compositor_fence **out_xcf)
{
        return xc->import_fence(xc, handle, out_xcf);
}
 
/*!
 * @copydoc xrt_compositor::create_semaphore
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_create_semaphore(struct xrt_compositor *xc,
                          xrt_graphics_sync_handle_t *out_handle,
                          struct xrt_compositor_semaphore **out_xcsem)
{
        return xc->create_semaphore(xc, out_handle, out_xcsem);
}
 
/*! @} */
 
/*!
 * @copydoc xrt_compositor::create_passthrough
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_create_passthrough(struct xrt_compositor *xc, const struct xrt_passthrough_create_info *info)
{
        return xc->create_passthrough(xc, info);
}
 
/*!
 * @copydoc xrt_compositor::create_passthrough_layer
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_create_passthrough_layer(struct xrt_compositor *xc, const struct xrt_passthrough_layer_create_info *info)
{
        return xc->create_passthrough_layer(xc, info);
}
 
/*!
 * @copydoc xrt_compositor::destroy_passthrough
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_destroy_passthrough(struct xrt_compositor *xc)
{
        return xc->destroy_passthrough(xc);
}
 
/*!
 * @name Session methods
 * @{
 */
 
/*!
 * @copydoc xrt_compositor::begin_session
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_begin_session(struct xrt_compositor *xc, const struct xrt_begin_session_info *info)
{
        return xc->begin_session(xc, info);
}
 
/*!
 * @copydoc xrt_compositor::end_session
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_end_session(struct xrt_compositor *xc)
{
        return xc->end_session(xc);
}
 
/*! @} */
 
 
/*!
 * @name Frame-related methods
 * @brief Related to the OpenXR `xr*Frame` functions
 * @{
 */
 
/*!
 * @copydoc xrt_compositor::predict_frame
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_predict_frame(struct xrt_compositor *xc,
                       int64_t *out_frame_id,
                       int64_t *out_wake_time_ns,
                       int64_t *out_predicted_gpu_time_ns,
                       int64_t *out_predicted_display_time_ns,
                       int64_t *out_predicted_display_period_ns)
{
        return xc->predict_frame(             //
            xc,                               //
            out_frame_id,                     //
            out_wake_time_ns,                 //
            out_predicted_gpu_time_ns,        //
            out_predicted_display_time_ns,    //
            out_predicted_display_period_ns); //
}
 
/*!
 * @copydoc xrt_compositor::mark_frame
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_mark_frame(struct xrt_compositor *xc, int64_t frame_id, enum xrt_compositor_frame_point point, int64_t when_ns)
{
        return xc->mark_frame(xc, frame_id, point, when_ns);
}
 
/*!
 * @copydoc xrt_compositor::wait_frame
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_wait_frame(struct xrt_compositor *xc,
                    int64_t *out_frame_id,
                    int64_t *out_predicted_display_time,
                    int64_t *out_predicted_display_period)
{
        return xc->wait_frame(xc, out_frame_id, out_predicted_display_time, out_predicted_display_period);
}
 
/*!
 * @copydoc xrt_compositor::begin_frame
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_begin_frame(struct xrt_compositor *xc, int64_t frame_id)
{
        return xc->begin_frame(xc, frame_id);
}
 
/*!
 * @copydoc xrt_compositor::discard_frame
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_discard_frame(struct xrt_compositor *xc, int64_t frame_id)
{
        return xc->discard_frame(xc, frame_id);
}
 
/*! @} */
 
 
/*!
 * @name Layer submission methods
 * @brief Equivalent to `xrEndFrame`, but split across multiple calls.
 * @{
 */
 
/*!
 * @copydoc xrt_compositor::layer_begin
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_begin(struct xrt_compositor *xc, const struct xrt_layer_frame_data *data)
{
        return xc->layer_begin(xc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_projection
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_projection(struct xrt_compositor *xc,
                          struct xrt_device *xdev,
                          struct xrt_swapchain *xsc[XRT_MAX_VIEWS],
                          const struct xrt_layer_data *data)
{
        return xc->layer_projection(xc, xdev, xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_projection_depth
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_projection_depth(struct xrt_compositor *xc,
                                struct xrt_device *xdev,
                                struct xrt_swapchain *xsc[XRT_MAX_VIEWS],
                                struct xrt_swapchain *d_xsc[XRT_MAX_VIEWS],
                                const struct xrt_layer_data *data)
{
        return xc->layer_projection_depth(xc, xdev, xsc, d_xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_quad
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_quad(struct xrt_compositor *xc,
                    struct xrt_device *xdev,
                    struct xrt_swapchain *xsc,
                    const struct xrt_layer_data *data)
{
        return xc->layer_quad(xc, xdev, xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_cube
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_cube(struct xrt_compositor *xc,
                    struct xrt_device *xdev,
                    struct xrt_swapchain *xsc,
                    const struct xrt_layer_data *data)
{
        return xc->layer_cube(xc, xdev, xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_cylinder
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_cylinder(struct xrt_compositor *xc,
                        struct xrt_device *xdev,
                        struct xrt_swapchain *xsc,
                        const struct xrt_layer_data *data)
{
        return xc->layer_cylinder(xc, xdev, xsc, data);
}
 
 
/*!
 * @copydoc xrt_compositor::layer_equirect1
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_equirect1(struct xrt_compositor *xc,
                         struct xrt_device *xdev,
                         struct xrt_swapchain *xsc,
                         const struct xrt_layer_data *data)
{
        return xc->layer_equirect1(xc, xdev, xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_equirect2
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_equirect2(struct xrt_compositor *xc,
                         struct xrt_device *xdev,
                         struct xrt_swapchain *xsc,
                         const struct xrt_layer_data *data)
{
        return xc->layer_equirect2(xc, xdev, xsc, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_passthrough
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_passthrough(struct xrt_compositor *xc, struct xrt_device *xdev, const struct xrt_layer_data *data)
{
        return xc->layer_passthrough(xc, xdev, data);
}
 
/*!
 * @copydoc xrt_compositor::layer_commit
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_FIRST
static inline xrt_result_t
xrt_comp_layer_commit(struct xrt_compositor *xc, xrt_graphics_sync_handle_t sync_handle)
{
        return xc->layer_commit(xc, sync_handle);
}
 
/*!
 * @copydoc xrt_compositor::layer_commit_with_semaphore
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_layer_commit_with_semaphore(struct xrt_compositor *xc, struct xrt_compositor_semaphore *xcsem, uint64_t value)
{
        return xc->layer_commit_with_semaphore(xc, xcsem, value);
}
 
/*! @} */
 
/*!
 * @copydoc xrt_compositor::get_display_refresh_rate
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_get_display_refresh_rate(struct xrt_compositor *xc, float *out_display_refresh_rate_hz)
{
        return xc->get_display_refresh_rate(xc, out_display_refresh_rate_hz);
}
 
/*!
 * @copydoc xrt_compositor::request_display_refresh_rate
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_request_display_refresh_rate(struct xrt_compositor *xc, float display_refresh_rate_hz)
{
        return xc->request_display_refresh_rate(xc, display_refresh_rate_hz);
}
 
 
/*!
 * @copydoc xrt_compositor::set_performance_level
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_set_performance_level(struct xrt_compositor *xc, enum xrt_perf_domain domain, enum xrt_perf_set_level level)
{
        return xc->set_performance_level(xc, domain, level);
}
 
/*!
 * @copydoc xrt_compositor::get_reference_bounds_rect
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_get_reference_bounds_rect(struct xrt_compositor *xc,
                                   enum xrt_reference_space_type reference_space_type,
                                   struct xrt_vec2 *bounds)
{
        if (xc->get_reference_bounds_rect == NULL) {
                return XRT_ERROR_NOT_IMPLEMENTED;
        }
 
        return xc->get_reference_bounds_rect(xc, reference_space_type, bounds);
}
 
/*!
 * @copydoc xrt_compositor::destroy
 *
 * Helper for calling through the function pointer: does a null check and sets
 * xc_ptr to null if freed.
 *
 * @public @memberof xrt_compositor
 */
XRT_NONNULL_ALL static inline void
xrt_comp_destroy(struct xrt_compositor **xc_ptr)
{
        struct xrt_compositor *xc = *xc_ptr;
        if (xc == NULL) {
                return;
        }
 
        xc->destroy(xc);
        *xc_ptr = NULL;
}
 
/*!
 * @name Function pointers for extensions
 * @{
 */
 
/*!
 * @brief Set thread attributes according to thread type
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_set_thread_hint(struct xrt_compositor *xc, enum xrt_thread_hint hint, uint32_t thread_id)
{
        return xc->set_thread_hint(xc, hint, thread_id);
}
 
/*! @} */
 
/*
 *
 * OpenGL interface.
 *
 */
 
/*!
 * Base class for an OpenGL (ES) client swapchain.
 *
 * @ingroup xrt_iface comp_client
 * @extends xrt_swapchain
 */
struct xrt_swapchain_gl
{
        //! @public Base
        struct xrt_swapchain base;
 
        // GLuint
        unsigned int images[XRT_MAX_SWAPCHAIN_IMAGES];
};
 
/*!
 * Down-cast helper.
 *
 * @private @memberof xrt_swapchain_gl
 *
 * @todo unused - remove?
 */
static inline struct xrt_swapchain_gl *
xrt_swapchain_gl(struct xrt_swapchain *xsc)
{
        return (struct xrt_swapchain_gl *)xsc;
}
 
 
/*
 *
 * Vulkan interface.
 *
 */
 
/*!
 * Base class for a Vulkan client swapchain.
 *
 * @ingroup xrt_iface comp_client
 * @extends xrt_swapchain
 */
struct xrt_swapchain_vk
{
        //! @public Base
        struct xrt_swapchain base;
 
        //! Images to be used by the caller.
        VkImage images[XRT_MAX_SWAPCHAIN_IMAGES];
};
 
/*!
 * Down-cast helper.
 *
 * @private @memberof xrt_swapchain_vk
 *
 * @todo unused - remove?
 */
static inline struct xrt_swapchain_vk *
xrt_swapchain_vk(struct xrt_swapchain *xsc)
{
        return (struct xrt_swapchain_vk *)xsc;
}
 
#if defined(XRT_HAVE_D3D11) || defined(XRT_DOXYGEN)
 
/*
 *
 * D3D11 interface.
 *
 */
 
/*!
 * Base class for a D3D11 client swapchain.
 *
 * @ingroup xrt_iface comp_client
 * @extends xrt_swapchain
 */
struct xrt_swapchain_d3d11
{
        //! @public Base
        struct xrt_swapchain base;
 
        //! Images to be used by the caller.
        ID3D11Texture2D *images[XRT_MAX_SWAPCHAIN_IMAGES];
};
 
/*!
 * Graphics usage requirements for D3D APIs.
 *
 * @ingroup xrt_iface
 */
struct xrt_d3d_requirements
{
        LUID adapter_luid;
        D3D_FEATURE_LEVEL min_feature_level;
};
 
#endif // XRT_OS_WINDOWS
 
 
#if defined(XRT_HAVE_D3D12) || defined(XRT_DOXYGEN)
/*
 *
 * D3D12 interface.
 *
 */
 
/*!
 * Base class for a D3D12 client swapchain.
 *
 * @ingroup xrt_iface comp_client
 * @extends xrt_swapchain
 */
struct xrt_swapchain_d3d12
{
        //! @public Base
        struct xrt_swapchain base;
 
        //! Images to be used by the caller.
        ID3D12Resource *images[XRT_MAX_SWAPCHAIN_IMAGES];
};
 
#endif
 
/*
 *
 * Native interface.
 *
 * These types are supported by underlying native buffers, which are DMABUF file
 * descriptors on Linux.
 *
 */
 
/*!
 * A single image of a swapchain based on native buffer handles.
 *
 * @ingroup xrt_iface comp
 * @see xrt_swapchain_native, xrt_graphics_buffer_handle_t
 */
struct xrt_image_native
{
        /*!
         * Native buffer handle.
         */
        xrt_graphics_buffer_handle_t handle;
 
        /*!
         * @brief Buffer size in memory.
         *
         * Optional, set to 0 if unknown at allocation time.
         * If not zero, used for a max memory requirements check when importing
         * into Vulkan.
         */
        uint64_t size;
 
        /*!
         * Is the image created with a dedicated allocation or not.
         */
        bool use_dedicated_allocation;
 
        /*!
         * Is the native buffer handle a DXGI handle?
         *
         * - If true, it is some kind of weird global handle, not reference counted, but
         *   widely compatible with various images. Ostensibly deprecated, but works the best
         *   on Windows.
         * - If false, it's either not Windows, or a reference counted "NT Handle"
         *   which has awkward limitations, such as "usually no depth images allowed".
         */
        bool is_dxgi_handle;
};
 
/*!
 * @interface xrt_swapchain_native
 * Base class for a swapchain that exposes a native buffer handle to be imported
 * into a client API.
 *
 * @ingroup xrt_iface comp
 * @extends xrt_swapchain
 */
struct xrt_swapchain_native
{
        //! @public Base
        struct xrt_swapchain base;
 
        /*!
         * Unique id for the swapchain, only unique for the current process, is
         * not synchronized between service and any apps via the IPC layer.
         */
        xrt_limited_unique_id_t limited_unique_id;
 
        struct xrt_image_native images[XRT_MAX_SWAPCHAIN_IMAGES];
};
 
/*!
 * @copydoc xrt_swapchain_reference
 *
 * @relates xrt_swapchain_native
 */
static inline void
xrt_swapchain_native_reference(struct xrt_swapchain_native **dst, struct xrt_swapchain_native *src)
{
        xrt_swapchain_reference((struct xrt_swapchain **)dst, (struct xrt_swapchain *)src);
}
 
/*!
 * @interface xrt_compositor_native
 *
 * Main compositor server interface.
 *
 * @ingroup xrt_iface comp
 * @extends xrt_compositor
 */
struct xrt_compositor_native
{
        //! @public Base
        struct xrt_compositor base;
};
 
/*!
 * @brief Create a native swapchain with a set of images.
 *
 * A specialized version of @ref xrt_comp_create_swapchain, for use only on @ref
 * xrt_compositor_native.
 *
 * Helper for calling through the base's function pointer then performing the
 * known-safe downcast.
 *
 * The pointer pointed to by @p out_xsc has to either be NULL or a valid
 * @ref xrt_swapchain pointer. If there is a valid @ref xrt_swapchain
 * pointed by the pointed pointer it will have it reference decremented.
 *
 * @public @memberof xrt_compositor_native
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_comp_native_create_swapchain(struct xrt_compositor_native *xcn,
                                 const struct xrt_swapchain_create_info *info,
                                 struct xrt_swapchain_native **out_xscn)
{
        struct xrt_swapchain *xsc = NULL; // Has to be NULL.
 
        xrt_result_t ret = xrt_comp_create_swapchain(&xcn->base, info, &xsc);
        if (ret == XRT_SUCCESS) {
                // Need to unref any swapchain already there first.
                xrt_swapchain_native_reference(out_xscn, NULL);
 
                // Already referenced.
                *out_xscn = (struct xrt_swapchain_native *)xsc;
        }
 
        return ret;
}
 
/*!
 * @copydoc xrt_compositor::destroy
 *
 * Helper for calling through the function pointer: does a null check and sets
 * xcn_ptr to null if freed.
 *
 * @public @memberof xrt_compositor_native
 */
XRT_NONNULL_ALL static inline void
xrt_comp_native_destroy(struct xrt_compositor_native **xcn_ptr)
{
        struct xrt_compositor_native *xcn = *xcn_ptr;
        if (xcn == NULL) {
                return;
        }
 
        xcn->base.destroy(&xcn->base);
        *xcn_ptr = NULL;
}
 
/*!
 * Holds information about the view configuration properties for a view in a system compositor.
 */
struct xrt_view_config_properties
{
        struct
        {
                uint32_t width_pixels;
                uint32_t height_pixels;
                uint32_t sample_count;
        } recommended; //!< Recommended for this view.
 
        struct
        {
                uint32_t width_pixels;
                uint32_t height_pixels;
                uint32_t sample_count;
        } max; //!< Maximums for this view.
};
 
struct xrt_view_config
{
        //! Which view type this is for, mono, stereo, quad_with_inset, etc...
        enum xrt_view_type view_type;
 
        //! Must match the view_type, in the future view_types might have variable views.
        uint32_t view_count;
 
        //! The per view information.
        struct xrt_view_config_properties views[XRT_MAX_COMPOSITOR_VIEW_CONFIGS_VIEW_COUNT];
};
 
 
/*
 *
 * System composition: how to composite on a system, either directly or by combining layers from multiple apps
 *
 */
 
/*!
 * Capabilities and information about the system compositor (and its wrapped native compositor, if any),
 * and device together.
 */
struct xrt_system_compositor_info
{
        uint32_t view_type_count;
        enum xrt_view_type view_types[XRT_MAX_COMPOSITOR_VIEW_CONFIGS_COUNT];
 
        //! Maximum number of composition layers supported, never changes.
        uint32_t max_layers;
 
        /*!
         * Blend modes supported by the system (the combination of the
         * compositor and the HMD capabilities), never changes.
         *
         * In preference order. Based on the modes reported by the device,
         * but the compositor has a chance to modify this.
         */
        enum xrt_blend_mode supported_blend_modes[XRT_BLEND_MODE_MAX_ENUM];
 
        //! Number of meaningful elements in xrt_system_compositor_info::supported_blend_modes
        uint8_t supported_blend_mode_count;
 
        uint32_t refresh_rate_count;
        float refresh_rates_hz[XRT_MAX_SUPPORTED_REFRESH_RATES];
 
        //! The vk device as used by the compositor, never changes.
        xrt_uuid_t compositor_vk_deviceUUID;
 
        //! The vk device suggested for Vulkan clients, never changes.
        xrt_uuid_t client_vk_deviceUUID;
 
        //! The (Windows) LUID for the GPU device suggested for D3D clients, never changes.
        xrt_luid_t client_d3d_deviceLUID;
 
        //! Whether @ref client_d3d_deviceLUID is valid
        bool client_d3d_deviceLUID_valid;
 
        //! Whether submitting projection layers of a differing FOV from the target FOV is supported.
        bool supports_fov_mutable;
 
        /*!
         * The compositor supports emulating quad views with insets even if the
         * device is only a stereo device. The views are split into two stereo
         * projections layers by the state trackers and tagged with the correct
         * layer type tags.
         *
         * This only needs to be set if the compositor hasn't exposed a
         * view_configs with the XRT_VIEW_TYPE_QUAD type, as that will also
         * cause the state tracker to submit split quad views with stereo
         * devices.
         */
        bool supports_emulated_quad_views_with_inset;
};
 
/*!
 * Details about the currently running session of an xrt_compositor.
 *
 * @related xrt_multi_compositor_control
 */
struct xrt_compositor_session_running_state
{
        //! Whether or not this session has been begun.
        bool running;
        //! The active view type of the session
        enum xrt_view_type active_view_type;
};
 
struct xrt_system_compositor;
 
/*!
 * @interface xrt_multi_compositor_control
 * Special functions to control multi session/clients.
 * Effectively an optional aspect of @ref xrt_system_compositor
 * exposed by implementations that can combine layers from multiple sessions/clients.
 */
struct xrt_multi_compositor_control
{
        /*!
         * Sets the state of the compositor, generating any events to the client
         * if the state is actually changed. Input focus is enforced/handled by
         * a different component but is still signaled by the compositor.
         */
        xrt_result_t (*set_state)(struct xrt_system_compositor *xsc,
                                  struct xrt_compositor *xc,
                                  bool visible,
                                  bool focused,
                                  int64_t timestamp_ns);
 
        /*!
         * Set the rendering Z order for rendering, visible has higher priority
         * then z_order but is still saved until visible again. This a signed
         * 64 bit integer compared to a unsigned 32 bit integer in OpenXR, so
         * that non-overlay clients can be handled like overlay ones.
         */
        xrt_result_t (*set_z_order)(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, int64_t z_order);
 
        /*!
         * Set the chroma key parameters for the base app's projection layers.
         * This is used to punch holes through opaque projection layers and adjust their blend mode.
         * Uses HSV min/max range for flexible color targeting.
         *
         * @param hsv_min Minimum HSV bounds
         * @param hsv_max Maximum HSV bounds
         * @param curve Power curve for alpha falloff
         * @param despill Despill strength
         */
        xrt_result_t (*set_base_chroma_key_params)(struct xrt_system_compositor *xsc,
                                                   struct xrt_colour_hsv_f32 hsv_min,
                                                   struct xrt_colour_hsv_f32 hsv_max,
                                                   float curve,
                                                   float despill);
 
        /*!
         * Tell this client/session if the main application is visible or not.
         */
        xrt_result_t (*set_main_app_visibility)(struct xrt_system_compositor *xsc,
                                                struct xrt_compositor *xc,
                                                bool visible);
 
        /*!
         * Notify this client/session if the compositor is going to lose the ability of rendering.
         *
         * @param loss_time_ns System monotonic timestamps, such as returned by os_monotonic_get_ns().
         */
        xrt_result_t (*notify_loss_pending)(struct xrt_system_compositor *xsc,
                                            struct xrt_compositor *xc,
                                            int64_t loss_time_ns);
 
        /*!
         * Notify this client/session if the compositor lost the ability of rendering.
         */
        xrt_result_t (*notify_lost)(struct xrt_system_compositor *xsc, struct xrt_compositor *xc);
 
        /*!
         * Notify this client/session if the display refresh rate has been changed.
         */
        xrt_result_t (*notify_display_refresh_changed)(struct xrt_system_compositor *xsc,
                                                       struct xrt_compositor *xc,
                                                       float from_display_refresh_rate_hz,
                                                       float to_display_refresh_rate_hz);
 
        /*!
         * This function returns the state of the currently running session.
         */
        xrt_result_t (*session_get_running_state)(struct xrt_system_compositor *xsc,
                                                  struct xrt_compositor *xc,
                                                  struct xrt_compositor_session_running_state *out_running_state);
};
 
/*!
 * The system compositor handles composition for a system.
 * It is not itself a "compositor" (as in xrt_compositor), but it can create/own compositors.
 * - In a multi-app capable system, the system compositor may own an internal compositor, and
 *   xrt_system_compositor::create_native_compositor will
 *   create a compositor that submits layers to a merging mechanism.
 * - In a non-multi-app capable system, xrt_system_compositor::create_native_compositor
 *   creates normal, native compositors, that do not wrap or feed into any other compositor.
 *
 * This is a long lived object: it has the same life time as an XrSystemID.
 */
struct xrt_system_compositor
{
        /*!
         * An optional aspect/additional interface, providing multi-app control.
         * Populated if this system compositor supports multi client controls.
         */
        struct xrt_multi_compositor_control *xmcc;
 
        //! Info regarding the system.
        struct xrt_system_compositor_info info;
 
        /*!
         * Create a new native compositor.
         *
         * This signals that you want to start XR, and as such implicitly brings
         * up a new session. Does not "call" `xrBeginSession`.
         *
         * Some system compositors might only support one `xrt_compositor`
         * active at a time, will return `XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED`
         * if this is the case.
         *
         * In a multi-session capable system compositor, this may return a "proxy"
         * for feeding a single client's layers to a compositor or a layer merging mechanism,
         * rather than a raw native compositor (not wrapping or forwarding) directly.
         */
        xrt_result_t (*create_native_compositor)(struct xrt_system_compositor *xsc,
                                                 const struct xrt_session_info *xsi,
                                                 struct xrt_session_event_sink *xses,
                                                 struct xrt_compositor_native **out_xcn);
 
        /*!
         * Gets the view configuration for the specified view type.
         */
        xrt_result_t (*get_view_config)(struct xrt_system_compositor *xsc,
                                        enum xrt_view_type view_type,
                                        struct xrt_view_config *out_view_config);
 
        /*!
         * Teardown the system compositor.
         *
         * The state tracker must make sure that no compositors are alive.
         */
        void (*destroy)(struct xrt_system_compositor *xsc);
};
 
/*!
 * @copydoc xrt_multi_compositor_control::set_state
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_compositor_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_set_state(
    struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible, bool focused, int64_t timestamp_ns)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->set_state(xsc, xc, visible, focused, timestamp_ns);
}
 
/*!
 * @copydoc xrt_multi_compositor_control::set_z_order
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_compositor_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_set_z_order(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, int64_t z_order)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->set_z_order(xsc, xc, z_order);
}
 
 
/*!
 * @copydoc xrt_multi_compositor_control::set_main_app_visibility
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_compositor_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_set_main_app_visibility(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->set_main_app_visibility(xsc, xc, visible);
}
 
/*!
 * @copydoc xrt_multi_compositor_control::notify_loss_pending
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_compositor_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_notify_loss_pending(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, int64_t loss_time_ns)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->notify_loss_pending(xsc, xc, loss_time_ns);
}
 
/*!
 * @copydoc xrt_multi_compositor_control::notify_lost
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_compositor_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_notify_lost(struct xrt_system_compositor *xsc, struct xrt_compositor *xc)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->notify_lost(xsc, xc);
}
 
/*!
 * @copydoc xrt_multi_compositor_control::notify_display_refresh_changed
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_composition_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_notify_display_refresh_changed(struct xrt_system_compositor *xsc,
                                           struct xrt_compositor *xc,
                                           float from_display_refresh_rate_hz,
                                           float to_display_refresh_rate_hz)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->notify_display_refresh_changed(xsc, xc, from_display_refresh_rate_hz,
                                                         to_display_refresh_rate_hz);
}
 
/*!
 * @copydoc xrt_multi_compositor_control::session_get_running_state
 *
 * Helper for calling through the function pointer.
 *
 * If the system compositor @p xsc does not implement @ref xrt_multi_composition_control,
 * this returns @ref XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_session_get_running_state(struct xrt_system_compositor *xsc,
                                      struct xrt_compositor *xc,
                                      struct xrt_compositor_session_running_state *out_running_state)
{
        if (xsc->xmcc == NULL) {
                return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
        }
 
        return xsc->xmcc->session_get_running_state(xsc, xc, out_running_state);
}
 
/*!
 * @copydoc xrt_system_compositor::create_native_compositor
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_create_native_compositor(struct xrt_system_compositor *xsc,
                                     const struct xrt_session_info *xsi,
                                     struct xrt_session_event_sink *xses,
                                     struct xrt_compositor_native **out_xcn)
{
        return xsc->create_native_compositor(xsc, xsi, xses, out_xcn);
}
 
/*!
 * @copydoc xrt_system_compositor::get_view_config
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_syscomp_get_view_config(struct xrt_system_compositor *xsc,
                            enum xrt_view_type view_type,
                            struct xrt_view_config *out_view_config)
{
        return xsc->get_view_config(xsc, view_type, out_view_config);
}
 
/*!
 * @copydoc xrt_system_compositor::destroy
 *
 * Helper for calling through the function pointer: does a null check and sets
 * xcn_ptr to null if freed.
 *
 * @public @memberof xrt_system_compositor
 */
XRT_NONNULL_ALL static inline void
xrt_syscomp_destroy(struct xrt_system_compositor **xsc_ptr)
{
        struct xrt_system_compositor *xsc = *xsc_ptr;
        if (xsc == NULL) {
                return;
        }
 
        xsc->destroy(xsc);
        *xsc_ptr = NULL;
}
 
 
/*
 *
 * Image allocator.
 *
 */
 
/*!
 * Allocator for system native images, in general you do not need to free the
 * images as they will be consumed by importing them to the graphics API.
 *
 * @see xrt_image_native
 */
struct xrt_image_native_allocator
{
        /*!
         * Allocate a set of images suitable to be used to back a swapchain
         * with the given create info properties (@p xsci).
         */
        xrt_result_t (*images_allocate)(struct xrt_image_native_allocator *xina,
                                        const struct xrt_swapchain_create_info *xsci,
                                        size_t image_count,
                                        struct xrt_image_native *out_images);
 
        /*!
         * Free the given images.
         */
        xrt_result_t (*images_free)(struct xrt_image_native_allocator *xina,
                                    size_t image_count,
                                    struct xrt_image_native *images);
 
        /*!
         * Destroy the image allocator.
         */
        void (*destroy)(struct xrt_image_native_allocator *xina);
};
 
/*!
 * @copydoc xrt_image_native_allocator::xrt_images_allocate
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_image_native_allocate
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_images_allocate(struct xrt_image_native_allocator *xina,
                    const struct xrt_swapchain_create_info *xsci,
                    size_t image_count,
                    struct xrt_image_native *out_images)
{
        return xina->images_allocate(xina, xsci, image_count, out_images);
}
 
/*!
 * @copydoc xrt_image_native_allocator::images_free
 *
 * Helper for calling through the function pointer.
 *
 * @public @memberof xrt_image_native_allocate
 */
XRT_NONNULL_ALL static inline xrt_result_t
xrt_images_free(struct xrt_image_native_allocator *xina, size_t image_count, struct xrt_image_native *images)
{
        return xina->images_free(xina, image_count, images);
}
 
/*!
 * @copydoc xrt_image_native_allocator::destroy
 *
 * Helper for calling through the function pointer: does a null check and sets
 * xina_ptr to null if freed.
 *
 * @public @memberof xrt_image_native_allocator
 */
XRT_NONNULL_ALL static inline void
xrt_images_destroy(struct xrt_image_native_allocator **xina_ptr)
{
        struct xrt_image_native_allocator *xina = *xina_ptr;
        if (xina == NULL) {
                return;
        }
 
        xina->destroy(xina);
        *xina_ptr = NULL;
}
 
 
/*!
 * @}
 */
 
 
#ifdef __cplusplus
}
#endif