Simple Qt5 app causes strange overlay to appear on screen
Submitted by Bruce Merry
Assigned to mes..@..op.org
Created attachment 98089 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 (151a20dc), configured with --with-dri-drivers=i965,swrast --with-gallium-drivers= which showed the same symptoms.
Attachment 98089, "Demonstration app showing the issue":