formula for replicating glTexGen in opengl es 2.0 glsl
- by visualjc
I also posted this on the main StackExchange, but this seems like a better place, but for give me for the double post if it shows up twice.
I have been trying for several hours to implement a GLSL replacement for glTexGen with GL_OBJECT_LINEAR. For OpenGL ES 2.0. In Ogl GLSL there is the gl_TextureMatrix that makes this easier, but thats not available on OpenGL ES 2.0 / OpenGL ES Shader Language 1.0
Several sites have mentioned that this should be "easy" to do in a GLSL vert shader. But I just can not get it to work.
My hunch is that I'm not setting the planes up correctly, or I'm missing something in my understanding.
I've pored over the web. But most sites are talking about projected textures, I'm just looking to create UV's based on planar projection. The models are being built in Maya, have 50k polygons and the modeler is using planer mapping, but Maya will not export the UV's. So I'm trying to figure this out.
I've looked at the glTexGen manpage information:
g = p1xo + p2yo + p3zo + p4wo
What is g? Is g the value of s in the texture2d call?
I've looked at the site:
http://www.opengl.org/wiki/Mathematics_of_glTexGen
Another size explains the same function:
coord = P1*X + P2*Y + P3*Z + P4*W
I don't get how coord (an UV vec2 in my mind) is equal to the dot product (a scalar value)? Same problem I had before with "g".
What do I set the plane to be? In my opengl c++ 3.0 code, I set it to [0, 0, 1, 0] (basically unit z) and glTexGen works great.
I'm still missing something.
My vert shader looks basically like this:
WVPMatrix = World View Project Matrix.
POSITION is the model vertex position.
varying vec4 kOutBaseTCoord;
void main()
{
gl_Position = WVPMatrix * vec4(POSITION, 1.0);
vec4 sPlane = vec4(1.0, 0.0, 0.0, 0.0);
vec4 tPlane = vec4(0.0, 1.0, 0.0, 0.0);
vec4 rPlane = vec4(0.0, 0.0, 0.0, 0.0);
vec4 qPlane = vec4(0.0, 0.0, 0.0, 0.0);
kOutBaseTCoord.s = dot(vec4(POSITION, 1.0), sPlane);
kOutBaseTCoord.t = dot(vec4(POSITION, 1.0), tPlane);
//kOutBaseTCoord.r = dot(vec4(POSITION, 1.0), rPlane);
//kOutBaseTCoord.q = dot(vec4(POSITION, 1.0), qPlane);
}
The frag shader
precision mediump float;
uniform sampler2D BaseSampler;
varying mediump vec4 kOutBaseTCoord;
void main()
{
//gl_FragColor = vec4(kOutBaseTCoord.st, 0.0, 1.0);
gl_FragColor = texture2D(BaseSampler, kOutBaseTCoord.st);
}
I've tried texture2DProj in frag shader
Here are some of the other links I've looked up
http://www.gamedev.net/topic/407961-texgen-not-working-with-glsl-with-fixed-pipeline-is-ok/
Thank you in advance.
