Add a clipping rectangle to the stack
int PtClipAdd( PtWidget_t *widget, PhRect_t *rect );
This function adds a clipping rectangle to the clipping stack. The rectangle added to the clipping stack is the intersection of the last rectangle on the stack and the rectangle defined in the PhRect_t pointed to by rect.
Prior to entering a widget's Draw method, the canvas rectangle derived from the PtBasic-class level is pushed onto the clipping stack. This prevents any children from drawing beyond the canvas of the parent container.
A widget can, however, draw beyond its own canvas or extent unless additional clipping is performed. PtAttemptResize() and PtResizeCanvas() set the Pt_UCLIP bit of a widget's resize flags if the widget requires additional clipping (to prevent it from drawing beyond its own canvas).
The current level of stack clipping.
PhRect_t, PtCalcCanvas(), PtClipRemove()
PtAttemptResize(), PtResizeCanvas() in Building Custom Widgets