1st, invert the Y: 10, 10 -> 10, 90
2nd, add origin: 10, 90 -> 0, 80 (no, not right--err, yes, it is)
-3rd, aply zoom: 0, 80 -> 0, 40
+3rd, apply zoom: 0, 80 -> 0, 40
or, is it:
1st, invert the Y: 10, 10 -> 10, 90
-2nd, aply zoom: 10, 90 -> 5, 45
+2nd, apply zoom: 10, 90 -> 5, 45
3rd, add origin: 5, 45 -> -5, 35
it depends on whether or not origin is in Qt coords or cartesian. If Qt, then the 1st