int xosd_set_shadow_offset (xosd* osd, int shadow_offset);
To increase readability (and 'cos it looks cool) a black shadow is
drawn beneath the main XOSD window.
changes the size of this shadow by altering how many pixels the shadow
is offset (to the bottom-right) from the main display.
One to four pixels usually is sufficient to get a good effect.
The on-screen display object to act on.
Offset of black shadow from main text, in pixels.
On success, a zero is returned.
On error, -1 is returned.