hi ,
function update() is used to paint all the area, and update(const QRegion & rgn) is used to paint rgn area. After calling the update() or update(const QRegion & rgn), function paintEvent will be called. I have a doubt about that, no matter I call the function update() or the function update(const QRegion & rgn), function paintevent will be called, and then my program will paint all area (because function paintEvent will paint all area).

so i think update() has no different with update(const QRegion & rgn). Is that right?
I want to know the reason .

I'm sorry about my poor english, but I really want to know the answer.

thanks very mush