c/render: Add scaffolding for sub-allocating UBOs

src/xrt/compositor/render/render_gfx.c

@@ -534,6 +534,9 @@ render_gfx_init(struct render_gfx *rr, struct render_resources *r)
 	    &rr->views[1].mesh.descriptor_set); // descriptor_set
 	VK_CHK_WITH_RET(ret, "vk_create_descriptor_set", false);
 
+	// Used to sub-allocate UBOs from, restart from scratch each frame.
+	render_sub_alloc_tracker_init(&rr->ubo_tracker, &r->gfx.shared_ubo);
+
 	return true;
 }
 

src/xrt/compositor/render/render_interface.h

@@ -386,6 +386,18 @@ struct render_resources
 		VkSampler clamp_to_border_black;
 	} samplers;
 
+	struct
+	{
+		/*!
+		 * Shared UBO buffer that we sub-allocate out of, this is to
+		 * have fewer buffers that the kernel needs to validate on
+		 * command submission time.
+		 *
+		 * https://registry.khronos.org/vulkan/site/guide/latest/memory_allocation.html
+		 */
+		struct render_buffer shared_ubo;
+	} gfx;
+
 	struct
 	{
 		//! The binding index for the source texture.
@@ -782,6 +794,9 @@ struct render_gfx
 	//! Resources that we are based on.
 	struct render_resources *r;
 
+	//! Shared buffer that we sub-allocate UBOs from.
+	struct render_sub_alloc_tracker ubo_tracker;
+
 	//! The current target we are rendering too, can change during command building.
 	struct render_gfx_target_resources *rtr;
 

src/xrt/compositor/render/render_resources.c

@@ -656,6 +656,45 @@ render_resources_init(struct render_resources *r,
 	VK_CHK_WITH_RET(ret, "vkAllocateCommandBuffers", false);
 
 
+	/*
+	 * Gfx.
+	 */
+
+	{
+		VkBufferUsageFlags usage_flags = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT;
+		VkMemoryPropertyFlags memory_property_flags = //
+		    VK_MEMORY_PROPERTY_HOST_COHERENT_BIT |    //
+		    VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT;      //
+
+		uint32_t num_buffers = 0;
+
+		// Number of layer shader runs (views), number of layers, two UBOs per layer.
+		num_buffers += RENDER_MAX_LAYER_RUNS * RENDER_MAX_LAYERS * 2;
+
+		// Two mesh distortion runs with one UBO each.
+		num_buffers += 2;
+
+		// We currently use the aligmnent as max UBO size.
+		static_assert(sizeof(struct render_gfx_mesh_ubo_data) <= RENDER_ALWAYS_SAFE_UBO_ALIGNMENT, "MAX");
+
+		// Calculate size.
+		VkDeviceSize size = num_buffers * RENDER_ALWAYS_SAFE_UBO_ALIGNMENT;
+
+		ret = render_buffer_init(  //
+		    vk,                    // vk_bundle
+		    &r->gfx.shared_ubo,    // buffer
+		    usage_flags,           // usage_flags
+		    memory_property_flags, // memory_property_flags
+		    size);                 // size
+		VK_CHK_WITH_RET(ret, "render_buffer_init", false);
+
+		ret = render_buffer_map( //
+		    vk,                  // vk_bundle
+		    &r->gfx.shared_ubo); // buffer
+		VK_CHK_WITH_RET(ret, "render_buffer_map", false);
+	}
+
+
 	/*
 	 * Mesh static.
 	 */
@@ -961,6 +1000,9 @@ render_resources_close(struct render_resources *r)
 	D(ImageView, r->mock.color.image_view);
 	D(Image, r->mock.color.image);
 	DF(Memory, r->mock.color.memory);
+
+	render_buffer_close(vk, &r->gfx.shared_ubo);
+
 	D(DescriptorSetLayout, r->mesh.descriptor_set_layout);
 	D(PipelineLayout, r->mesh.pipeline_layout);
 	D(PipelineCache, r->pipeline_cache);