Texel Buffers (Uniform + Storage)

[hrydgard]

Vulkan Texel buffers are (potentially) large 1-D images that are not backed by image objects, instead they're backed by a VkBufferView specifying a range (and format, for free conversion) of a VkBuffer.

These can be either read-only (Uniform Texel Buffers) or read/write (Storage Texel Buffers).

The corresponding SPIR-V can be found at https://github.com/KhronosGroup/GLSL/blob/master/extensions/khr/GL_KHR_vulkan_glsl.txt#L370 .

Essentially, it's just texelFetch on an image with Dim = Buffer.

Historically, they are yet another historical artifact that predate storage buffers, they existed as a special kind of 1D textures in OpenGL to access large arbitrary data. Effectively it's using a texture unit on a linear buffer, so they still have advantages such as free format conversion from packed integer formats to float, and accessing unaligned formats like R32G32B32_FLOAT , which is good in raytracing shaders for grabbing vertex data through bindless arrays of these for doing stuff like normal or UV coordinate interpolation after a hit

#450 is related.

[XAMPPRocky]

so they still have advantages such as free format conversion from packed integer formats to float, and accessing unaligned formats like R32G32B32_FLOAT

Are formats like R32G32B32_FLOAT required? AFAICT SPIR-V doesn't have those in the spec, and doesn't have an extension that adds them.

[XAMPPRocky]

Both Uniform and Storage Texel Buffers are implemented in #359. With that PR you'd write the types from your example as follows:

use spirv_std::Image;

type UniformBuffer = Image!(buffer, type=f32, sampled);
type StorageBuffer = Image!(buffer, format=r32f, sampled=false);

[hrydgard]

Very cool!

@XAMPPRocky SPIR-V doesn't care about the specific format for those cases. It's like a texture, conversion happens on load and the exact format is specified when binding the texture. And yeah I think that's just supported for the Uniform variant.

[XAMPPRocky]

these are now available in main.