Question

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Glut Mouse Coordinates

Let’s say that I have a window of 600×600.
When I receive mouse events I don’t know what’s the real position of the mouse, in OpenGL I use this to draw points:

(-0.5,0.5) | (0.5,0.5)
           |
 --------(0,0)-------
           |
           |
(-0.5,-0.5) | (0.5,-0.5)

But when I receive GLUT mouse events depending on the size of the window I get different coordinates.I want a relative (to the window) coordinate system.How do I get this?

Answer 1

I am pretty sure glut gives you the mouse coordinates in window space (i.e. if the window is 800×600 and the mouse position is in the middle, it will give you x: 400, y: 300), so if you want to bring that to the opengl space you posted above, you would do the following:

float x = (400 / 800) - 0.5f; //0.0
float y = (300 / 600) - 0.5f; //0.0

so a generic version would look something like this:

float mouseX = (theGlutMouseXCoordinate / theGlutWindowWidth) - 0.5f;
float mouseY = (theGlutMouseYCoordinate / theGlutWindowHeight) - 0.5f;