VertexBuffer

VertexBuffer

The third step in the DXR series: read vertex data from the closest-hit shader.

The previous sample only used geometry for intersection. Here, the vertex buffer is also exposed as a StructuredBuffer<Vertex> so the shader can interpolate color with barycentric coordinates.

What You Learn

• Create a vertex buffer with position and color.
• Create a structured-buffer SRV.
• Add a t1 descriptor for vertex data.
• Use PrimitiveIndex() inside the closest-hit shader.
• Interpolate attributes with BuiltInTriangleIntersectionAttributes.

DXR Flow

1. Create a buffer with three vertices.
2. The BLAS uses positions from that same buffer to describe the triangle.
3. Create a structured SRV so HLSL can read the buffer.
4. The root signature exposes:
   • t0: TLAS.
   • t1: StructuredBuffer<Vertex>.
   • u0: output texture.
5. The closest-hit shader computes the triangle vertex indices.
6. The shader interpolates colors with u, v, and w.

Key Shader

uint triIndex = PrimitiveIndex();

Vertex v0 = gVertices[triIndex * 3 + 0];
Vertex v1 = gVertices[triIndex * 3 + 1];
Vertex v2 = gVertices[triIndex * 3 + 2];

float u = attribs.barycentrics.x;
float v = attribs.barycentrics.y;
float w = 1.0 - u - v;

payload.color = v0.color * w + v1.color * u + v2.color * v;

Build

cmake --build build --config Debug --target VertexBuffer

Run

.\build\Debug\VertexBuffer.exe