[Pharo-project] How to redraw only a part of a morph

Hi! I try to optimize the graphic framework I'm porting. I have good performance but I have some problem to reDraw the morph of my view. When I reDraw my morph I use 'invalidRect:' with the bound of the part I want to reDraw but every step my morph is entirely reDraw. Does I have to use another method? Or someone can explain me how pharo manage the repaint of morph? Thanks :) I will ask today if I can make a video of my work because is very impressive of what we can do on Pharo with the framework! And if the reDraw is functional we certainly have the same performance with Pharo! So good news :) Tristan