[PyQt] QGraphicsScene background

[Lee Harr]

>> in long-running programs                                                                            
>> when many many items have been added, the scene                                                                              
>> starts to slow down.

> Did you checked the navigation pad example? It uses some tricks, e.g. by
> (optionally) using OpenGL and various transformations, that might be
> helpful for your issue, too.

Thanks Pete. I will take a deeper look at that example.

I am a bit worried at the start, though. Running that example
on my old laptop locked up the whole system (required a hard
reboot) and on my desktop it fails with OpenGL errors:

QGLShader: could not create shader 
Vertex shader for simpleShaderProg (MainVertexShader & PositionOnlyVertexShader) failed to compile
QGLShader: could not create shader 
Fragment shader for simpleShaderProg (MainFragmentShader & ShockingPinkSrcFragmentShader) failed to compile
QGLShaderProgram: could not create shader program 
Errors linking simple shader: "" 
QGLShader: could not create shader 
Vertex shader for blitShaderProg (MainWithTexCoordsVertexShader & UntransformedPositionVertexShader) failed to compile
QGLShader: could not create shader 
Fragment shader for blitShaderProg (MainFragmentShader & ImageSrcFragmentShader) failed to compile
QGLShaderProgram: could not create shader program 
Errors linking blit shader: "" 
QGLShader: could not create shader 
Warning: "" failed to compile! 


Commenting out the QGLWidget viewport allows the program
to run, but I'd be leery of using something in my application that
can fail so spectacularly.