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Pixel to world coords for asymmetrical ortho projection


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#1 pondwater   Members   -  Reputation: 191

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Posted 17 January 2013 - 05:34 PM

I am modifying some existing code that has a 2D orthographic projection set as:

 

glOrtho(-0.02, 1.02, -0.02, 0.68, -1, 1);

 

I have never had an issue with transfering pixel coords (mouse clicks specifically) into world space when the left/right, top/bottom values of the frustum are symmetrical.

 

I simply convert the pixel values to a normalize -1 to 1 'window coord' centered in the middle of the window and then scale those values by the right/top values given to my frustum.

 

But for some reason I am getting really confused when converting to this asymmetrical frustum.

 

This should be simple, but I can't for the life of me figure it out!

 

EDIT:

 

I feel silly now, I figured it out:

// normalized window coords centered on bottom left of window
float x = (pixel_x / window_width);
float y = (window_height - pixel_y)/(window_height);

// world coords by scaling and translating
x = x*(frustum_right - frustum_left ) - frustum_left;
y = y*(frustum_top - frustum_bottom) - frustum_bottom;

Edited by pondwater, 17 January 2013 - 05:54 PM.


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