Am 10.08.2021 um 15:09 schrieb Henri Verbeet hverbeet@gmail.com:
For the "left" part of "top-left"; we don't flip the x-axis, but we still want to make sure we get the convention Direct3D applications expect.
My head is flipping upside down every time I think too much about coordinate systems, but I think that's wrong. We aren't rotating everything by 180 degrees around z - we're flipping around the x axis, swapping front and back. As evidence, we have to adjust the winding order based on yflip.
If you twist a clock in such a way that it now runs counterclockwise and 6 is at the top and 12 at the bottom, then 9 will still be on the left and 3 on the right. Or like a mirror on the floor you are standing on. Your left and right will be alright, but suddenly your up and down are flipped and the watch will still run counterclockwise in the reflection. In the situation you are thinking of (6 top, 12 bottom, 3 left, 9 right) the clock still runs clockwise.
Am I missing something? I am sure that even if my thinking is right I've got some part of the explanation wrong...