Incorrect coordinate mapping in ScreenToGLCoords and GLToScreenCoords.

[db47h]

Unless I'm mistaken, screen X coordinates are in the range [0, screenWidth-1], not [0, screenWidth] (the same applies to the Y coordinate), and GL's coordinate system maps [screenWidth-1,0] to [1.0,1.0] and [0,screenHeight-1] to [-1.0,-1.0].

So the code for ScreenToGLCoords should be:

func ScreenToGLCoords(x, y int, screenWidth, screenHeight int) (xOut, yOut float64) {
	xOut = 2.0*float64(x)/float64(screenWidth-1) - 1.0
	yOut = -2.0*float64(y)/float64(screenHeight-1) + 1.0

	return
}

[UserAB1236872]

Hey, sorry, I've been working double-long hackathon-level days at work recently. If you submit a PR I'd be glad to accept it, but it will probably have to wait a few weeks otherwise.

[db47h]

No worries, PR incoming.

As I wrote a test for the fix, I found out that GLToScreenCoords inverts the sign of the returned y-coordinate. So that'll get fixed as well.

Reminder to self: trivial tests for trivial functions are not that useless 😉