Our first shader 🟠

Resulting code: step019-next

We have introduced how to allocate GPU memory in chapter Playing with buffers, and we now see how to run a custom program on the GPU.

GPU Pipelines

There are similarities and differences between the way programs run on a CPU and on a GPU.

Like a CPU, a GPU can be programmed. The program is written in a human language, then compiled into a binary representation. Traditionally, a GPU program is called a shader program.

The programming languages used to program a GPU are different from the ones used to program a CPU. This is because the computing models are quite different, and in particular a GPU cannot allocate/free memory for itself. We can cite for instance GPU languages like GLSL, HLSL, MSL, Slang, etc. and the one we’ll be using: WGSL (“SL” stands for Shader Language).

GPU programs are fundamentally parallel, following a Single Instruction/Multiple Data model: the execution pointer (address of the currently executed instruction) is shared among neighbor threads, only they fetch and process slightly different data. This enables the hardware to mutualize some operations like memory access, which is key to data-intensive applications.

Besides programmable stages, a GPU also features fixed-function stages. It typically contains hardware circuits dedicated to some performance critical operations. A canonical example of such stage is the rasterization, which projects 3D triangles onto the pixels of a texture. Fixed-function stages can be configured through some options, but are not programmable.

What we call a pipeline is a series of fixed-function with a specific configuration and programmable stages with a given shader.

WIP

Conclusion

Resulting code: step019-next