View Full Version : Window coordinates - simple question

04-30-2009, 12:11 PM
If I have a pair of (x,y) window coordinates (where the mouse clicked in an opengl view) how do I find the corresponding coordinates of that click in terms of the opengl world space? I'm using gluPerspective for a 3d perspective projection matrix.

I've looked around but I'm not sure what the official name for this is, which makes it hard to search.


04-30-2009, 01:45 PM
You can't get 3D coordinates from 2D coordinates because the projection loses information. However if you have the depth as well then you can use:
glReadPixels(x,y,GL_DEPTH_COMPONENT, GL_FLOAT, &depth);
gluUnProject(x,y,depth, model_view, projection, viewport, &outX, &outY, &outZ);
See documentation for explanation of the function.

Typically this sort of thing is called "picking" because when user clicks somewhere inside a window, you project a ray into 3D and return the intersection with the first object. That's kind of what the code above does - the depth component will contain the z for the closest object.