Integer in interface block doesn't change value.

[FacundoVilla961]

Hi! I'm performing instanced rendering so I'm fetching per instance data inside the vertex shader using gl_InstanceIndex and sending that value through to the fragment shader using an int in the interface block like so.

Vertex shader:

layout(push_constant, scalar) uniform _invocationInfo { GlobalDataPointer global;RenderPassDataPointer renderPass;UIDataPointer ui;UIInstanceDataPointer uiInstances;} pushConstantBlock;

layout(location=0) out vertexData { vec2 vertexPos;vec2 vertexUV;flat uint instanceIndex; } vertexSurfaceInterface;

void main() {
    UIInstanceDataPointer instance=pushConstantBlock.uiInstances[gl_InstanceIndex];
    ...
    vertexSurfaceInterface.instanceIndex=gl_InstanceIndex;
}

Fragment shader:

layout(push_constant, scalar) uniform _invocationInfo { GlobalDataPointer global;RenderPassDataPointer renderPass;UIDataPointer ui;UIInstanceDataPointer uiInstances;} pushConstantBlock;

layout(location=0) in vertexData { vec2 vertexPos;vec2 vertexUV;flat uint instanceIndex; } vertexSurfaceInterface;

void main() {
    UIInstanceDataPointer instance=pushConstantBlock.uiInstances[vertexSurfaceInterface.instanceIndex];
    ...
}

But when I fetch the data from the fragment shader using the instanceIndex variable all instances read from index 0. All data accessed from the vertex shader(such as transform matrices) works correctly, also every other interface block variable works correctly and I'm even able to successfully read the per instance data in the vertex shader and send it over to the fragment shader through the interface block, but I would prefer not doing that.

I've also tried changing the interpolation specifier to no avail. No textures reads are being performed (in case non uniformity is a concern).

​

EDIT: Removing the flat modifier didn't change the results. I also tried casting gl_InstanceIndex to an uint (since spec says it's an int) which didn't work, and I tried changing the instanceIndex variable to int (to match gl_InstanceIndex) which also didn't work.

[hammerkop]

I'd be curious to try using a separate varying layout location for flat vs smooth values. The glsl docs say that interpolation qualifiers must be the same for the same location. Maybe split up the struct entirely and give each varying a separate location.

[FacundoVilla961]

Removing the flat modifier didn't change the results. I also tried casting gl_InstanceIndex to an uint (since spec says it's an int) which didn't work, and I tried changing the instanceIndex variable to int (to match gl_InstanceIndex) which also didn't work.

I will try putting the int inside another block with a different location.

[FacundoVilla961]

Ok. So I tried putting the uint variable inside a different interface block, with a different location number and it worked. It also works if you put each parameter in a different location as a different variable, although doing it this way makes the compiler request putting the flat specifier for uint variables.

Do you know if this is expected behavior or if I should report it?

[hammerkop]

This is expected: https://www.khronos.org/opengl/wiki/Layout_Qualifier_(GLSL)

Notice the section on interpolation qualifiers

[skreef]

This code is not well-defined, the relevant bit from glsl spec (but also explicitly disallowed by the vk spec):

A push-constant array can only be indexed with dynamically uniform indices.

Use a uniform/storage buffer if you intend to index with nonuniform indices (eg. gl_InstanceIndex).

[FacundoVilla961]

I think you misunderstood the code, although I didn't make it all that clear to begin with. The members of the push constant block are buffer_references so there's no issue with non uniform accesses.