Simple question, if I paint outside a component bounds, does Juce perform the paint operation for these external pixels (which would use some CPU time)?
I ask it to know if I need to optimize my code in component::paint() (or it's a waste of time)
It depends.
Some operations are very easy to clip, others are not. Drawing a rectangle that's too big will take no extra time at all, but other things, e.g. a complex text layout, may be slow.
It also depends on the rendering engine - the CoreGraphics engine will behave differently to the software/GL engines.
So, the only correct advice is the same answer as for any performance-related question: Measure it, don't make any assumptions!
Thank you. It did worth doing, since I saved around 70 times the CPU time.