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Introducing Vulkan Ray Tracing Position Fetch Extension

On April 27, 2023 the Vulkan® Ray Tracing TSG released the VK_KHR_ray_tracing_position_fetch extension, which exposes the ability to fetch vertex positions from an acceleration structure hit when tracing rays. The SPIR-V SPV_KHR_ray_tracing_position_fetch and GLSL GL_EXT_ray_tracing_position_fetch extensions have also been released to provide SPIR-V and GLSL support for this functionality.

The position of scene geometry is provided to ray tracing acceleration structures at build time and they include a derived form of the positions to enable efficient ray tracing and queries. Applications frequently require the position or a derived attribute of a triangle on a hit. For example, the geometric normal of the hit can be used as a biased ray origin for shadow rays in path tracers to prevent self intersection. The Ray Tracing Position Fetch extension enables direct retrieval of position and attribute information to avoid duplication of geometry data storage.