Then I think the routine is made to do that. That is, you swap the coordinates and then call the routine, and the routine does what it's made to do, takes lines pointing upward or downward, and swap the coordinates to draw all lines downward.
To fix it, look in the routine. There should be a subtract to create delta values for X and Y. Then, look for a test for the sign of delta Y. Reverse the test.
But if it's optimized, it's not made for that (only has 4/8 octants, the downward pointing ones). This means a rewrite of the routine.
Last edited by Photon; 19 February 2021 at 12:25.
