[Mesa-dev] [Bug 78010] New: Simple Qt5 app causes strange overlay to appear on screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78010

          Priority: medium
            Bug ID: 78010
          Assignee: mesa-dev at lists.freedesktop.org
           Summary: Simple Qt5 app causes strange overlay to appear on
                    screen
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: bmerry at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: 10.1
         Component: GLX
           Product: Mesa

Created attachment 98089
  --> https://bugs.freedesktop.org/attachment.cgi?id=98089&action=edit
Demonstration app showing the issue

I'm not sure if this is a bug in Mesa or in Qt. But since the behaviour differs
depending on whether LIBGL_ALWAYS_SOFTWARE is set or not I think something
might be strange in Mesa, which is why I'm filing this here first.

I have reduced the problem to a very simple Qt5 application (which I will
attach). It has a QGLWidget, which simply calls glClear. When I run the
application, a window (with no decorations) seems to appear over part of the
screen, at the same size as the widget. It initially shows through to whatever
was on the desktop behind it, but the contents are not updated.

Additionally, the GL widget does not seem to be filled in: it starts with
whatever the background was, and doesn't update. However, if I set
LIBGL_ALWAYS_SOFTWARE=1, then it correctly shows as pink (however, the other
symptom remains).

System information:
OS: Xubuntu 14.04
CPU: i5-2430M

glxinfo, without environment variables:
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile 
OpenGL core profile version string: 3.1 (Core Profile) Mesa 10.1.0
OpenGL core profile shading language version string: 1.40

glxinfo, with LIBGL_ALWAYS_SOFTWARE=1
OpenGL vendor string: VMware, Inc.
OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 3.4, 256 bits)
OpenGL version string: 2.1 Mesa 10.1.0
OpenGL shading language version string: 1.30

I've also tried using Mesa git (151a20d), configured with
--with-dri-drivers=i965,swrast --with-gallium-drivers=
which showed the same symptoms.

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