ray_tracing_position_fetch

Position Fetch

Only the information provided by the acceleration structure is used to raytrace an object. The positions are fetched and the geometric normal is calculated from them. All buffers used to create the acceleration structures are deleted before rendering. This makes the rendering extremely lightweight.

You can find more information on VK_KHR_ray_tracing_position_fetch in this blog: https://www.khronos.org/blog/introducing-vulkan-ray-tracing-position-fetch-extension

Implementation

As usual, follow the #FETCH for what is specific to the sample.

createBottomLevelAS()

The flag VK_BUILD_ACCELERATION_STRUCTURE_ALLOW_DATA_ACCESS_KHR needed to be added to the bottom acceleration structure.

main()

And the following extention was needed too:

 VkPhysicalDeviceRayTracingPositionFetchFeaturesKHR fetchFeatures{VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_RAY_TRACING_POSITION_FETCH_FEATURES_KHR};
  spec.vkSetup.addDeviceExtension(VK_KHR_RAY_TRACING_POSITION_FETCH_EXTENSION_NAME, false, &fetchFeatures);  // #FETCH

raytrace.chit

In the shader we are using gl_HitTriangleVertexPositionsEXT[n] to retrieve the 3 triangle positions.