I have watched the video on cursor.c, and I understand that the goal is to put a circle (oval) on top of the mouse cursor, but I don't get the math of the formula used. I see that it's a kindergarten issue, but still I would be grateful for help.

X coordinate of event - radius of circle and Y coordinate of event - diameter of circle.

The circle appears at X = 0, Y = 0. When I move the mouse cursor, why the circle appears on top is I subtract it's radius from X of the cursor and diameter from Y of the cursor?

1 Answer 1


Got it! Sorry! It's because the values of axis are reversed, not like in ordinary math :)

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