if i set a clipping region and then need to reset it to the origin
(whole screen shall be painted), i have to differ between the different device-resolutions.
i could be lazy and choose only a region, whioch covers the largest screen-resolution (e.g. 200x200). then i wouldnt need
to store the actual height and width of the screen or getting it out of the canvas.
but: is there any performance difference between choosing the suitable clipping region and choosing a much bigger one ?