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Doggan

Vertex Shader - verts to NDC

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I am trying to transform the vertices of a polygon into NDC coordinates (0 to 1) to be used as UV texture coordinates. This is being done in a vertex shader. It seems simple enough. (You can imagine a small rectangle polygon on the screen. It should then be as if I am using scissoring or clip planes to ONLY render the part of the scene that falls within those polygon boundaries). Here is what I am doing:
void main(void)
{
	vec4 pos = ftransform();
	gl_Position = pos;

        // This turns the position into NDC coordinates, ranging -1 to 1.
	vec2 ndcPos = vec2(pos.x / pos.w, pos.y / pos.w);

        // Now turn that into a 0 to 1.0 range.
	ndcPos = vec2((pos.x + 1.0) / 2.0, (pos.y + 1.0) / 2.0);

        // Use that as the texture coordinate.
	gl_TexCoord[0].s = ndcPos.x;
	gl_TexCoord[0].t = ndcPos.y;
}
The fragment shader is simply:
gl_FragColor = texture2D(tex, gl_TexCoord[0].st);
Something is clearly not right, because when I debug (painting red in pixels where the U/V are 0-1 and green when outside the range), the window is mostly green with a much-too-small red box that enlarges as I move very close. When the polygon is on-screen, it should always been red, right? Any ideas? This seems like it should be easy to do.
edit: dumb typo :((( [Edited by - Doggan on October 2, 2007 5:30:32 AM]

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