QGLWidget 2d painting performance

[wysota]

Try modifying the demo so that it draws some pixmap on each chip.

[amnesiac]

Try modifying the demo so that it draws some pixmap on each chip.

I will try that later on.

Another interesting detail is that a drawPixmap() takes half of the time than a bindTexture() does, which could either mean that drawPixmap does not make a texture conversion or bindTexture() has lots of overhead... or both

[wysota]

You can take a look at sources of the gl paint engine and check it out yourself.

[amnesiac]

You can take a look at sources of the gl paint engine and check it out yourself.

Well, I had a closer look at drawPixmap in class QOpenGLPaintEngine and indeed, they convert a QPixmap into a texture using bindTexture. But under certain circumstances they use the GL_TEXTURE_RECTANGLE_NV instead of GL_TEXTURE_2D option for binding, which seems to make the performance difference. Unfortunately in my code, this does not work (can't bind the texture). Has anyone experience on this?

Still I'd like to avoid this caching behavior, is there any way to avoid this and do a "normal" drawPixmap as QWidget does?

While playing around with QGLWidget I experienced a possible Qt bug. I'm using a QStackedWidget and 3 Widgets( 2 different views and a transition GLWidget). When I switch from the GLWidget to the new view, the former view is shown for one frame. But no paintevent is called in the old view. Looks like there's some old data in the video memory of the graphic card or something like that. Anyone experienced the same or knows how the get around this?

Regards,
André