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# Calculating window and mouse position (OpenGL)

Posted on 2004-04-04
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Aright, here's a good one, and I'll probably have to do ray casting (help), but I'm looking for something easier.

Here's the setup: I have a window (QUAD object) inside an OpenGL window. When I rotate the Window about the y-axis, I remap the mouse so that it projects down to the window, no matter which angle it is at (or am I making things to difficult?)
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Question by:rossryan

LVL 2

Expert Comment

ID: 10781121
Ok, I hope I understand you...
You're designing some sort of window system and the windows have some kind of animation or movement when they gain focus right? Like laying down to facing the camera?

Why does the mouse have to be in the window?  Is there something in there they need to click on?  Can you clarify what you're trying to do?
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Author Comment

ID: 10865843
Hmm. They do not lay face down. Take a look at Project Looking Glass. It's something comparable to that. They may be at an angle, and I think I need the normal to convert back to the angled windows real coordinates.
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LVL 2

Accepted Solution

enkimute earned 500 total points
ID: 10947782
Thats not so difficult.

Lets define some stuff :

Mw = Model View matrix used to transform your 'quad' from object space to world space. (you can get this from gl with glGetFloatfv)
P    = Projection matrix in your openGL setup. (same stuff .. glGetFloatfv)
Mpw = Mw * P = Modelview projection matrix, or the matrix you have to multiply the object space quad with to end up in screenspace. ( a simple matrix multiply )

IMpw = (Mpw)^ -1 = The inverse of the modelview projection matrix. If the original matrix is orthonormal, you can use a cheap matrix invert .. (thats true most of the time).

So multiplying a vertex with IMpw will transform it from screen space back to the object space of your original quad. So if you multiply the position of the mouse cursor
with the IMPw, you get a resulting position that you can correctly compare with the vertex positions of your 'quad'

Hope that clears it up for you !
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