Starting usdview on a system with a GL_VERSION of 3.0 shows errors in the console

[flashingsquare]

Description of Issue

Starting usdview on my system which supports OpenGl 3.0 prints a lot errors of the form:

0:1(10): error: GLSL 1.40 is not supported. Supported versions are: 1.10, 1.20, 1.30, 1.00 ES, 3.00 ES, 3.10 ES, and 3.20 ES

error: linking with uncompiled/unspecialized shadererror: linking with uncompiled/unspecialized shader
Traceback (most recent call last):
  File "/home/knud/src/c++/phanes/thirdparty/USD/build/build_usdimaging/lib/python/pxr/Usdviewq/stageView.py", line 1714, in paintGL
    self.DrawAxis(viewProjectionMatrix)
  File "/home/knud/src/c++/phanes/thirdparty/USD/build/build_usdimaging/lib/python/pxr/Usdviewq/stageView.py", line 1038, in DrawAxis
    glslProgram = self.GetSimpleGLSLProgram()
  File "/home/knud/src/c++/phanes/thirdparty/USD/build/build_usdimaging/lib/python/pxr/Usdviewq/stageView.py", line 1030, in GetSimpleGLSLProgram
    ["mvpMatrix", "color"])
  File "/home/knud/src/c++/phanes/thirdparty/USD/build/build_usdimaging/lib/python/pxr/Usdviewq/stageView.py", line 126, in __init__
    GL.glDeleteShader(vertexShader)
  File "src/errorchecker.pyx", line 53, in OpenGL_accelerate.errorchecker._ErrorChecker.glCheckError
OpenGL.error.GLError: GLError(
	err = 1281,
	description = 'invalid value',
	baseOperation = glDeleteShader,
	cArguments = (5L,)
)

Looking at the chart found here https://stackoverflow.com/questions/27407774/get-supported-glsl-versions/27410925 It looks like GL 3.0 is indeed mapped to GLSL version 1.3

Changing the lines starting at stageView.py:92

if (self._glMajorVersion >= 3):
    vsSource = VS3
    fsSource = FS3
else:
    vsSource = VS2
    fsSource = FS2

to

glslVersion = float(GL.glGetString(GL.GL_SHADING_LANGUAGE_VERSION))
if (glslVersion >= 1.4):
    vsSource = VS3
    fsSource = FS3
else:
    vsSource = VS2
    fsSource = FS2

Solved the problem for me since it now uses The supported fallback shaders VS2 and FS2
VS3 => #version 140
VS2 => #version 120

Steps to Reproduce

1. On a Linux machine with OpenGL version of 3.0 start usdview
2. See what happens

System Information (OS, Hardware)

Fedora 29

Package Versions

19.07

Build Flags

python ../build_scripts/build_usd.py --materialx --alembic --hdf5 --openimageio --usdview --usd-imaging --ptex /home/knud/src/c++/phanes/thirdparty/USD/build/build_usdimaging

[jilliene]

Filed as internal issue #USD-5636

[DuncanHopkinsFoundry]

I have seen this issue as well. Either on MacOS or using the open source MESA nVidia drivers.
I submitted PR 965 as a manual work around for this. Set up USDVIEW_ENABLE_COREGL environment variable and i allows drivers that support OpenGL Core context but expose an OpenGL Compatibility context that is less than the minimum 3.2 value of the Core context.

[flashingsquare]

I have to admit that I do not fully understand the relation to #965.
This bug (how I see it) stems from a wrong mapping of the OPENGL_VERSION to GL_SHADING_LANGUAGE_VERSION which results in selecting the wrong shader (1.4 instead of 1.2).
The current behavior is:
Get the _glMajorVersion by casting the version-string to an int.
From this _glMajorVersion select one of the two shader variants
glVersion >= 3 => select the shader with glsl-version 1.4 (VS3/FS3)
otherwise => select the shader with glsl-version 1.2 (VS2/FS2)

This is correct for all gl versions except for 3.0 since 3.0 maps to glsl-version 1.3 and should therefore select 1.2

glFormat.setProfile(QtOpenGL.QGLFormat.CoreProfile)
shouldn't do anything on my system since "QGLFormat::setProfile" is ignored for OpenGL versions of less than 3.2