Simplied Fullscreen-Triangle Shader in RadialBlur

[twanks123]

Hello Sasha,
i am referring to this line in radialBlur.vert:
outUV = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2); gl_Position = vec4(outUV * 2.0f - 1.0f, 0.0f, 1.0f);
With validation layers enabled it throws a performance warning at vkCmdDraw(...):
"Vertex Buffers are bound to command buffer but no vertex buffers are attached to this Pipeline State Object"
Is it allowed to do this neat trick in vulkan? I could find only these two lines in the spec:
1.) All vertex input bindings accessed via vertex input variables declared in the vertex shader entry point’s interface must have valid buffers bound
2.) For a given vertex buffer binding, any attribute data fetched must be entirely contained within the corresponding vertex buffer binding, as described in Section 20.2, “Vertex Input Description”

Does this mean know you shouldnt do this?
Greetings
SH

[SaschaWillems]

This is perfectly valid as long as you have a proper empty vertex input state for that pipeline (see https://github.com/SaschaWillems/Vulkan/blob/master/radialblur/radialblur.cpp#L696).

Seeing that this is just a performance warning, using this technique is fine, as the performance warnings may be a bit too strict. What version of the validation layers throws this warning?

[twanks123]

The newest one (1.0.30.0). And yes i have an empty vertex-input-state for the pipeline. Should i report this to LunarG?

[SaschaWillems]

The layers from the SDK usually lag behind, so it's best to test with layers compiled from sources.

Performance warnings are debatable though, so this one may make sense for certain implementations. But if still present with recent layers build from source it may be a good idea to bring up the discussion over at validation layer repo (https://github.com/KhronosGroup/Vulkan-LoaderAndValidationLayers/issues).

[SaschaWillems]

I just checked with the layers built from the latest sources and the performance warning is still there. IMO this is misleading, so I opened up an issue over at the validation layer repo: KhronosGroup/Vulkan-LoaderAndValidationLayers#1080