The PixmapRequest constructor expected width and height in logical
pixels, and scaled them to device pixels. However, not knowing what
screen the request is for, it had to use qApp->devicePixelRatio()
for the scaling. That value may not be correct if not all screens
use the same scaling.
Fix this by introducing a new constructor that takes the device
pixel ratio as an additional argument, and deprecating the old
constructor.
Oliver Sander