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World space coords in a fragment program

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Is there a quick and easy way to go from window coordinates (x E [0,width]; y E [0,height]; z E [0,1]) to world space coordinates in a fragment program? I'm currently passing in the inverse viewing transformation, doing a DP4 on each element (including w and doing the perspective divide). Is there an easier method? Also, in the fragment.position the last component (.w) is 1/w. What is this normally used for?

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Maybe my question is a little vague...

I want to transform each pixel from its window coordinates back to world space coordinates, and then operate on the pixel in world space coordinates (a depth replacement algorithm).

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if this was GLSL then I'd say use the gl_ModelViewProjectionMatrixInverse uniform (unless I'm going crazy that should do what you want it to...).. however, as it appears you arent, unless the fragment program interface has a simular mapping you'll have to work it out yourself and pass it to the program as a parameter of some kind

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Thanks for the reply..


I'm currently doing that...I use glProgramLocalParameter4dARB() and pass in the 4 rows of the inverse matrix.

I then take the x and y coords and divide them by the window width and height, and then take those along with the depth and do a MAD to convert them from [0,1] to [-1,1].

Then I do DP4 on each row...divide by w, yadda yadda...but I'm still not getting the correct values. It seems so straight foward, I feel I'm missing something very simple.

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