double buffering

[drhex]

I'd try calling update() or repaint() on the widget that has the pixmap, and probably processEvents too, but I'm sure there are more elegant ways.

[faldzip]

i would also suggest using layouts than setting the buttons positions manually

[HelloDan]

I'd try calling update() or repaint() on the widget that has the pixmap, and probably processEvents too, but I'm sure there are more elegant ways.

repaint()　is OK

Thanks

[HelloDan]

Why must I call repaint, but oneStep can do the same thing without call it?

[drhex]

Because when you draw in execOnce(), a flag is set indicating that an update is necessary. That flag is acted upon when the main event loop is run (after your slot has finished). runAll(), though, wants to do many updates without returning from the slot between each and so needs to do more explicit repainting.

[HelloDan]

Thanks to drhex