Layers: (SC) check PointSize valid usage

[karl-lunarg]

Issue by yavn (MIGRATED)
Friday Sep 23, 2016 at 13:37 GMT
Originally opened as KhronosGroup/Vulkan-LoaderAndValidationLayers#974

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This is a feature request.

It seems that Vulkan requires (similar to GLES) that PointSize is written in VS when the vertex pipeline is outputting points. It would be nice if layer could detect this situation and report an error if PointSize is not assigned to in the shader.

Please check the spec for details. From what I understood, this only applies if vertex shader is the only active vertex stage, and only if drawing points (VK_PRIMITIVE_TOPOLOGY_POINT_LIST). In other stages the point size is 1.0 by default and there are other rules (e.g. see shaderTessellationAndGeometryPointSize feature).

[karl-lunarg]

Comment by chrisforbes (MIGRATED)
Saturday Sep 24, 2016 at 02:40 GMT

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Seems like a reasonable thing to want, and shouldn't be a big deal to implement. I'm not convinced you've got the rules quite right, but I'll work from the spec.

[karl-lunarg]

Comment by jekstrand (MIGRATED)
Friday Jan 13, 2017 at 16:35 GMT

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+1 I just hit this in a CTS test where they were using tessellation with point_mode but weren't setting gl_PointSize in their tessellation evaluation shader. This comment serves as a note to the person working on this to remember tessellation!

The correct rules for this are fairly subtle. If you only have a vertex shader, then you must write gl_PointSize in the shader when using points. If you have a geometry or tessellation shader, then it depends on whether or not the shaderGeometryAndTessellationPointSize feature is enabled. If enabled, then you must write gl_PointSize in the last geometry shader stage. If disabled, then you must not write gl_PointSize and you get a default of 1.0.

[karl-lunarg]

Comment by zeux (MIGRATED)
Saturday Oct 28, 2017 at 03:55 GMT

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We've hit this issue as well - on some Android devices neglecting to output gl_PointSize results in a random value getting fed to the rasterizer, which can be hard to track down without a graphics debugger if the result of rasterization isn't directly visible on the screen...

IOW +1 - this is easy to miss and needs to be validated.

[mark-lunarg]

Need to address @chrisforbes review findings in PR #261.