Question

I think that’s what clip are used for but I can’t find any example to do this.
I need to:

• Limit the region by setting a new clipmask (altering the GC)
• Draw
• Set the GC back to its previous state

Answer 1

You can do it by using XSetClipRectangles() referenced here and XSetClipMask() referenced here

So:

Display dpy; //This is your display, we'll assume it is a valid Display
GC gc; //This is your GC, we'll assume it is a valid GC
XRectangle recs[]; //This is an array containing the clipping regions you want.
int recs_n; //This is the number of rectangles in the 'recs' array.

XSetClipRectangles(dpy, gc, 0, 0, recs, recs_n, Unsorted); //Enable clipping
drawMyClippedGraphics(); //Call to whatever you want to use for drawing
XSetClipMask(dpy, gc, None); //Restore the GC

For further information type man functionName in your terminal.