meshlets

Meshlet

Meshlet Data Structure

When we generate meshlets from the original vertex buffer and index buffer, we will get the following data structures:

struct Meshlet  
{  
    u32 vertex_offset;  
    u32 primitive_offset;  
  
    u32 vertex_count;  
    u32 primitive_count;  
};
 
std::vector<Meshlet> meshlets;
std::vector<u8> primitive_indices; // mostly triangles
std::vector<u32> vertex_indices;

The vertex buffer is left unchanged, and together, the information in the meshlet and the two new index buffers primitive_indices and vertex_indices can be used to retrieve the original index buffer.

Why We Have Two Index Buffers?

The purpose of the two index buffers is better data compression.

Consider the following original index buffer of triangles:

indices = { 4,5,6, 8,4,6, ...}

This will generate the following buffers:

vertex_indices = { 4,5,6, 8, ...}
// For the second triangle only vertex 8 must be added
// and the other vertices are re-used.
 
primitive_indices = { 0,1,2,  3,0,2, ...}
// the primitive indices are local per meshlet

Because a meshlet can’t have more than 256 vertices, primitive_indices only need to be stored in an u8 rather than a u32.

Given a meshlet, here is how to get the original index from those two buffers:

indices[i] = vertex_indices[primitive_indices[i] + meshlet.primitive_offset] + meshlet.vertex_offset

References

• Introduction to Turing Mesh Shaders | NVIDIA Technical Blog