Indicates that you are beginning the process of redrawing
region on the this's surface.
Calling this function begins a drawing operation using this on the surface that this was created from. The actual requirements and guarantees for the drawing operation vary for different implementations of drawing, so a CairoContext and a GLContext need to be treated differently.
A call to this function is a requirement for drawing and must be followed by a call to end_frame, which will complete the drawing operation and ensure the contents become visible on screen.
Note that the
region passed to this function is the minimum region that needs to be drawn and depending on implementation,
windowing system and hardware in use, it might be necessary to draw a larger region. Drawing implementation must use
get_frame_region to query the region that must be drawn.
the context used to draw the frame
minimum region that should be drawn