Here we rotate the coordinate system ang degrees counter-clockwise. Here we draw the barrel of the cannon. In this case, the coordinate system is first translated, then rotated. We're done, except that we haven't explained why Windows didn't dither this time. There is no single correct color allocation strategy.
Some strategies look good for some programs, some look bad.
CustomColor gives Qt applications better colors on Windows. It has no effect under X11. There are several options. You can read about them in the documentation . When the scroll bar is operated, the angle of the drawn cannon changes accordingly.