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POOpenGL custom rendering pipeline: Perspective matrix
 

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  1. POOpenGL custom rendering pipeline: Perspective matrix
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    <p>I am attempting to work in LWJGL to display a simple quad using my own matrices. I've been looking around for awhile and have found a few perspective matrix implementations, these two in particular:</p> <pre><code>[cot(fov/2)/a 0 0 0] [0 cot(fov/2) 0 0] [0 0 -f/(f-n) -1] [0 0 -f*n/(f-n) 0] </code></pre> <p>and:</p> <pre><code>[cot(fov/2)/a 0 0 0] [0 cot(fov/2) 0 0] [0 0 -(f+n)/(f-n) -1] [0 0 -(2*f*n)/(f-n) 0] </code></pre> <p>Both of these provide the same effect, as expected (got them from <a href="http://www.scratchapixel.com/lessons/3d-advanced-lessons/perspective-and-orthographic-projection-matrix/perspective-projection-matrix/" rel="nofollow">here</a> and <a href="http://www.lwjgl.org/wiki/index.php?title=The_Quad_with_Projection,_View_and_Model_matrices#Projection_matrix" rel="nofollow">here</a>, respectively). The issue is in my understanding of how multiplying this by the modelview matrix, then a vertex, then dividing each x, y, and z value by its w value gives a screen coordinate. More specifically, if I multiply either of these by the modelview matrix then by a vertex (10, 10, 0, 1), it gives a w=0. That in itself is a big smack in the face. I conclude either the matrices are wrong, or I am missing something completely. In my actual test program, the vertices don't even end up on screen even though the camera position at (0,0,0) and no rotation would make it so. I even have tried many different z values, positive and negative, to see if it was just a clipping plane. Am I missing something here?</p> <p>EDIT: After a lot of checking over, I've narrowed down the problem I am facing. The biggest issue is that the z-axis does not appear to be remapped to the range I specify (n to f). Any object just zooms in or out a little bit when I translate it along the z-axis then pops out of existence as it moves past the range [-1, 1]. I think this is also making me more confused. I set my far plane to 100 and my near to 0.1, and it behaves like anything but.</p>
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    1. COI already multiply in that order in my vertex shader. Thanks for the suggestion though.
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