从视口坐标转换为[-1,1] ^ 2顶点[OpenGL]

Question

G'day!

Say I have a mouse click represented by its integer values in the window (with the window being resizable), so its domain would be (0,0) - > (current_width, current_height). Is there an easy way to 'normalise' or convert this mouse click position to a vertex in OpenGL land? ie a point in R^2 with domain [-1,1]^2?

Eg: If the current width and height of the window was 400 and 600 respectively, and I clicked at 400,600, I'd like to easily convert that to [1,-1].

Does this functionality exist within OpenGL or will I have to write the function myself?

Cheers.

Answer 1

You'll have to write the function yourself, but it's trivial:

x_ogl = 2.0 * (x_mouse - width / 2) / width
y_ogl = -2.0 * (y_mouse - height / 2) / height

The negation in the second formula is to convert from "+ve Y down" in mouse / screen coordinates to more normal cartesian of "+ve Y up".

Also, it would be more conventional to maintain a 1:1 aspect ratio between X and Y coordinates with the larger axis maintaining the range [-1, 1] and the smaller axis having a smaller range.

If that's what you'd really prefer, then replace the right hand side of the outer division by max(width, height) in both of the two expressions above instead of as shown.