Question

I have to display a tiled map to display the result of a simulation
One can zoom/unzoom on the map, so if the zoom is far, there will be much more tiles displayed.

I am using QGraphicsPixmapItem to add the tiles to a QGraphicsScene.
I wonder whether openGl would be able to speed things up

Answer 1

I am using QGraphicsPixmapItem to add the tiles to a QGraphicsScene.

QGraphicsScene already uses methods like spatial subdivision (Kd trees) to determine which parts of a scene are visible and which not. In addition QGraphicsScene can use OpenGL as a rendering backend.

I strongly suggest you stick with QGraphicsScene, you’ll hardly get more efficient than this, especially considering your next question:

I wonder whether openGl would be able to speed things up

Not if used naively. OpenGL is not a scene graph. I can’t cull away and not issue drawing commands for geometry not visible. If you send it drawing commands it will process them. Unlike QGraphicsScene, which maintains scene data, OpenGL will carry out whatever drawing operation you ask it to do. Even if the final result may be invisible. Only in the very last processing steps (clipping, early fragment rejection) invisible fragments are discarded.