Bindless Tracking Issue

[kanerogers]

Overview

This issue tracks enabling various "bindless" functionality for the various native backends.

Partially bound descriptors

• Vulkan
• Partially bound descriptors on DX12 #3639
• Partially bound descriptors on Metal #3640
  • Use Argument Buffers on Metal #3334

Validation

• BindGroupLayoutEntry::count Validation Does Not Check That Shader Uses Binding Arrays #3648
• Array binding provided zero elements validation error when using PARTIALLY_BOUND_BINDING_ARRAY #3692

Performance

• Bind groups with binding arrays with high max count in their bind group layout take an extremely long time to allocate descriptor sets for #3729

[John-Nagle]

Bindless mode means you have a big table of all the texture objects in the GPU. Each of those texture objects is a GPU buffer. Buffers either belong to the GPU, and the CPU can't touch them, or they belong to the CPU, and the GPU can't touch them.

So the big table of texture object descriptors and the GPU buffer states have to be kept in sync. At the Vulkan level, this problem belongs to the program calling Vulkan. Vulkano, which is supposed to be a safe Rust interface to Vulkan, has machinery for maintaining that table. But WGPU doesn't have that machinery, so it can't do bindless yet, at least not safely.

GPU/CPU buffer ownership and the bindless descriptor table need to be managed together.

All the targets WGPU currently supports seem to support bindless mode. Even OpenGL, since 2013, has offered it as an extension. You do need OpenGL 4 with extensions, though. Everything in current release seems to have full support now, via Vulkan, Metal, or OpenGL.

The future is bindless. Unreal Engine is now bindless-only, I think.