GLSL vertex shaders and fog
Author
If I am just using a GLSL vertex shader and my GL_FOG_COORDINATE_SRC is set to default (GL_FRAGMENT_DEPTH), how do I get the fixed pipeline to handle the fog?
Do I set gl_FogFragCoord = abs((gl_ModelViewMatrix * pos).z) ?
When I do this, I get very strange colors.
Or do I have to use GL_FOG_COORDINATE and set the fog coordinates in order to access gl_FogCoord?
I don't recall having to do that with vertex shaders using Cg.
I'm only using a vertex shader for my object.
just a guess:
The vertex shader has a varying output variable gl_FogFragCoord (float). If the fragments are handled by the fixed function pipeline than it will use the default varying output and input variables.
Just try something like:
vec3 ecposition = vec3(gl_ModelViewMatrix * gl_Vertex);
gl_FogFragCoord = ecposition.z/ecposition.w;
The vertex shader has a varying output variable gl_FogFragCoord (float). If the fragments are handled by the fixed function pipeline than it will use the default varying output and input variables.
Just try something like:
vec3 ecposition = vec3(gl_ModelViewMatrix * gl_Vertex);
gl_FogFragCoord = ecposition.z/ecposition.w;
Author
Actually, that does not work on ATI cards. That is where I am having my problem. NVIDIA works ok.
Author
I have used a fragment shader to make it work on ATI, without the color anomalies. But the only purpose of this shader is to make foliage sway in the wind. I can do this with a vertex shader only. And it works on nVidia. But ATI gives me strange color anomalies. Reading the 2.0 spec, all I should have to do is give gl_FogFragCoord my eyepoint position, as shown in the previous post.(??)
I've noticed that ATI is less forgiving than nVidia with shader specs, so hopefully someone can point out what I am missing by using only a Vertex Shader.
I've noticed that ATI is less forgiving than nVidia with shader specs, so hopefully someone can point out what I am missing by using only a Vertex Shader.
Quote:Original post by Duel93This is just to point out that there's no prize in using FFP instead of a simple FFP-like shader stage. You're not winning anything and nobody will ever think this is an awesome idea, especially if when doing that, you run in this kind of issues.
I have used a fragment shader to make it work on ATI, without the color anomalies. But the only purpose of this shader is to make foliage sway in the wind. I can do this with a vertex shader only. And it works on nVidia. But ATI gives me strange color anomalies.
The fact that mixing FFP with shaders on ATi gives headaches is a point to leave FFP alone and begin starting to think that "it's better to do that with shaders anyway" for safety.
Author
I agree with your post. And to get it working, I have done just that.
I'm still curious about why it does not work on ATI. I don't like "not knowing".
I'm still curious about why it does not work on ATI. I don't like "not knowing".
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement