Instanced Drawing (🔴TODO)

Drawing the same geometry multiple times is very common. It happens when scattering objects like rocks or trees on a terrain, when drawing particle systems, etc.

Turns out that the GPU is particularly good at drawing such repeated geometry thanks to the mechanism of instancing.

Note

It is much more efficient than issuing multiple draw calls, not only because it avoids repeating the overhead of building a draw command, but also because it enables the GPU to better manage memory by streaming the instances through the rendering pipeline simultaneously.

Both the draw and drawIndexed methods of a render pipeline encoder support instancing (wgpuRenderPipelineEncoderDraw and wgpuRenderPipelineEncoderDrawIndexed) through their second argument.

renderPipeline.draw(vertexCount, instanceCount, 0, 0);

But as you will quickly notice if changing this instance count argument, all instances get drawn at the very same position!

A first solution to distinguish instances is in the shader, using the @builtin(instance_id) attribute in the vertex shader inputs.

TODO

A second solution is to use instance-level vertex attributes. TODO