ray_tracing_position_fetch

Position Fetch in Vulkan Ray Tracing

Overview

This implementation demonstrates the use of VK_KHR_ray_tracing_position_fetch extension in Vulkan. It enables raytracing using only the acceleration structure data, without additional vertex buffers.

Key aspects:

• Positions are fetched directly from the acceleration structure
• Geometric normals are calculated from retrieved positions
• All buffers used for acceleration structure creation are deleted pre-rendering
• Results in a lightweight rendering process

For detailed information: Vulkan Ray Tracing Position Fetch Extension

Implementation Details

Acceleration Structure Creation

// Add to bottom acceleration structure
VK_BUILD_ACCELERATION_STRUCTURE_ALLOW_DATA_ACCESS_KHR

Extension Enablement

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
);

Shader Implementation

In the closest hit shader (raytrace.chit):

vec3 vertex = gl_HitTriangleVertexPositionsEXT[n];