Shadow mapping without hardware support

PfhorSlayer · 2004-05-25T04:53:35

Hey, all. I'm currently working on trying to implement shadow mapping on my old GF2MX (Personal project, just to see if I can), and I've run into some trouble. I understand how shadow mapping is supposed to work, but I'm slightly hung up on trying to get the distance from the light to each fragment into the color buffer, which I can then use register combiner operations on to compare it to the light's depth-map texture that I've projected onto the scene. After thinking for a while, I realized that a vertex shader may be able to solve my problem. If I pass the light position and the near and far distances of the light's view frustum into a vertex shader that does the following: 1) Calculate the vertex's position in clip (is that the right one?) space 2) Subtract this position from the light's position, to get a vector that goes from the vertex to the light 3) Calculate the length of this vector 4) Subtract the near distance of the light's frustum from the far distance 5) Divide the distance from the light to the vertex by the (far - near) from above 6) Set the output vertex's colors to this value I should get a color buffer filled with depth values from each fragment to my light! I implemented this shader here. It seems to work alright, except that when comparing the values in the color buffer after using this shader, to the values in the color buffer after projecting the depth buffer from the light's perspective, the values in the Vertex Shaded buffer seem quite off. See what I mean: Distance (vertex shader) color buffer Depth map projected onto scene color buffer The balls in the distance one are far too white (the light is above, to the left, and a bit behind the scene shown); since they are closer to the light's near frustum plane than most of the rest of the scene, they should be darkest, but they are almost white. I'm pretty certain that my idea here, using the vertex shader to fill the color buffer with distance values, should work to achieve what I'm trying to do, and my register combiner code right now is not the issue (I'm testing this by outputting the depth map and distance textures to file, and subtracting the two). Any assistance would be greatly appreciated. Thanks, Dylan Barrie Postpose [edit] fixed the links, oops! [/edit] [edited by - PfhorSlayer on May 20, 2004 8:45:50 PM]

Graphics and GPU Programming Programming

Started by PfhorSlayer May 20, 2004 07:36 PM

9 comments, last by PfhorSlayer 19 years, 11 months ago

siaspete

208

May 25, 2004 04:53 AM

If it''s anything like D3D, since you''re using a vertex shader, setting OpenGL''s modelview matrix has no effect for vertices your shader processes.

So there is no harm in passing 2 matrices into your shader as constants instead:

* A model-view matrix (transforming from object space to camera space).
* AND a ''model'' matrix (called ''world'' in D3D, transforming from object space to world space).

Hope this helps.

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Shadow mapping without hardware support

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Shadow mapping without hardware support

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