csurface:MarkDirtyRectangle -- mark dirty rectangle
Synopsis
csurface:MarkDirtyRectangle(x, y, width, height)
Function
Like csurface:MarkDirty(), but drawing has been done only to
the specified rectangle, so that Cairo can retain cached contents
for other parts of the surface.
Any cached clip set on the surface will be reset by this function,
to make sure that future Cairo calls have the clip set that they
expect.