What is the "set" param in GLSL in godot's compute shader layout

[stebl]

Godot Version

4.2

Question

I’m reading the compute shader tutorial that describes an input data buffer like this,

layout(set = 0, binding = 0, std430) restrict buffer MyDataBuffer { ...

The docs say compute shaders are directly written in GLSL, so I’m referencing keywords with the GLSL docs.

I’ve found and understand:

• The memory layout specifier std430
• Binding points for buffer blocks (binding = 0)
• The restrict memory qualifier

But I cannot for the life of me find the docs for layout(set = 0).

The closest I’ve come are opaque references in the Vulkan docs.
IIUC, GLSL compiles to SPIR-V which then uses the Vulkan API, so Vulkan docs don’t exactly apply.

set basically seems like a way of specifying memory layout, but what does it mean at a driver/hardware level?
What’s the difference between set and binding? When does set need to increment?
Where can I learn more?

[pennyloafers]

https://www.reddit.com/r/vulkan/comments/zt87pv/confused_about_vulkan_binding_and_set_rules_in/

[stebl]

Thanks for the link. Does that imply there are multiple versions of GLSL? One targeting Vulkan and one targeting OpenGL? It also seems to imply Godot is using the Vulkan-targeted one.

For anyone following- the reddit thread references the GLSL language doc here - https://registry.khronos.org/OpenGL/specs/gl/GLSLangSpec.4.60.pdf

[pennyloafers]

@stebl

Does that imply there are multiple versions of GLSL?

Yes but GLSL is only a language.

@stebl

One targeting Vulkan and one targeting OpenGL?

Not for Godot. As I believe we are still on Opengl3… And that doesn’t support compute shaders. So It’s only Vulkan. I think the Godot shader language is probably a derivative of GLSL.

@stebl

seems to imply Godot is using the Vulkan-targeted one.

Yes it’s because compute shaders are a feature of the Vulkan sdk. Opengl does not support compute shaders in 3.x. And didnt until 4.3.