VSG built in flat shader doesn't compile

[hytel]

So, I'm taking the plunge, and upgrading my huge VSG application from 1.1.11 to 1.1.15 and I'm getting a crash on the first compile. To the console I get:

Warning: GLSL source failed to parse.
Warning: glslang info log:
ERROR: 0:69: '=' : cannot convert from ' global highp 4-component vector of float' to ' temp highp float'
ERROR: 0:69: '' : missing #endif
ERROR: 0:69: '' : compilation terminated
ERROR: 3 compilation errors. No code generated.

I can see line 69 which is:

69: float v = texture(diffuseMap, texCoordDiffuse);

Which indeed could be an error because texture should return a vec4 but it's being assigned to a single float value. I looked to see how I got this fragment shader and it appears to be because I called vsg::createFlatShadedShaderSet and it didn't have one in it's list, so it creates one using the binary array down in the shaders sub-folder:

VulkanSceneGraph-1.1.15\src\vsg\utils\shaders\flat_ShaderSet.cpp

It looks like this may have been changed in 1.1.14 to include this line.

Is this really an issue, or am I doing something wrong?

[robertosfield]

Can you reproduce the issue with any of vsgExamples?

What glslang version are you using?

[hytel]

When I do:

uint32_t glsl_major = VK_VERSION_MAJOR(properties.apiVersion);
uint32_t glsl_minor = VK_VERSION_MINOR(properties.apiVersion);

I get Vulkan 1.4 which should support GLSL up to 4.60 but your flat shader logic has:

#version 450

And this causes no issue, so I would imagine it's using 4.5 compiler for you shaderset. I'm on windows and it's very difficult to simply upgrade a project to use all new libraries like it is in Linux. It took me a long time to get vsgExamples compiled a year ago, and I'd rather not if I don't have to (mine is tied to the older 1.1.11 libraries). Probably anyone with a current vsg Examples 1.1.15 build could see this error in any of the examples that use flat shading (e.g. --flat). If there is no way for anyone to check this, I guess this is what I will have to do.

You can see in the relatively recent change set (Aug 1, 2025) for the VSG Examples flat shader:

   -     float v = texture(diffuseMap, texCoord[texCoordIndices.diffuseMap].st).s;
   -     diffuseColor *= vec4(v, v, v, 1.texCoordIndices.diffuseMap);
   +     float v = texture(diffuseMap, texCoordDiffuse);
   +     diffuseColor *= vec4(v, v, v, 1);

So the previous version before 1.1.14 was pulling a component out which is why the original I was using didn't complain.

[robertosfield]

I have just reviewed the vsgExamples/data/shaders versions of standard_pbr.frag and standard_phong.frag and both use .s when accessing the texture as greyscale so my best guess is that the standard_flat_shaded.frag should also use the .s and is simply a copy and paste bug that not been spotted due to be a rarely used shader combination.

[hytel]

That was my thought exactly, which is why I thought to bring it to your attention! Also, looks like most wouldn't notice because you'd have to build vsgExamples with vsgXchange, then try to load a model that utilizes the VSG_DIFFUSE_MAP material I think given the code in question is wrapped in VSG_DIFFUSE_MAP check (among others). I am loading many external models with various textures so I'm not surprised I see this.