Damage surface in surface-relative coordinates
In 9141196d positional coordinates were added to the damage call of pixmap flips. The damage box coordinates are in screen space though and we need to convert them first to surface-relative ones by substracting the origin of the window.
On current master Steam client does not work for me in KWinFT and Sway sessions. With the patch works again in both.
/cc @daenzer