cairo-surface-create-for-rectangle (target x y width height)

target -- an existing cairo-surface-t instance for which the sub-surface will point to
x -- a double float x-origin of the sub-surface from the top-left of the target surface, in device-space units
y -- a double float y-origin of the sub-surface from the top-left of the target surface, in device-space units
width -- a double float with the width of the sub-surface, in device-space units
height -- a double float with the height of the sub-surface, in device-space units

A pointer to the newly allocated surface. The caller owns the surface and should call the function cairo-surface-destroy when done with it. This function always returns a valid pointer, but it will return a pointer to a "nil" surface if other is already in an error state or any other error occurs.

Create a new surface that is a rectangle within the target surface. All operations drawn to this surface are then clipped and translated onto the target surface. Nothing drawn via this sub-surface outside of its bounds is drawn onto the target surface, making this a useful method for passing constrained child surfaces to library routines that draw directly onto the parent surface, i.e. with no further backend allocations, double buffering or copies. The semantics of subsurfaces have not been finalized yet unless the rectangle is in full device units, is contained within the extents of the target surface, and the target or subsurface's device transforms are not changed.