My scene contains virtualplanetbuilder-generated terrain that has a texture
wrapped on it along with surface objects such as trees that I generated by
creating osg primitives and coloring them "PER_VERTEX" without using any
textures.
I have written an atmospheric transmission shader that decreases the r,g and b
values as a function of distance from the viewer to the object. However, I
can't seem to get the shader to work properly on both the terrain and trees at
the same time. Here is the code:
Vertex Shader:
Code:
varying float eyeDistance;
void main(void)
{
gl_TexCoord[0] = gl_MultiTexCoord0;
gl_FrontColor = gl_Color;
eyeDistance = length(gl_ModelViewMatrix * gl_Vertex);
gl_Position = ftransform();
}
Fragment Shader:
Code:
uniform float ExtinctionCoefficient;
uniform sampler2D baseTexture;
varying float eyeDistance;
void main(void)
{
vec4 color = texture2D(baseTexture, gl_TexCoord[0].st);
color.r = color.r * exp( -1.0 * ExtinctionCoefficient * eyeDistance );
color.g = color.r;
color.b = color.r;
gl_FragColor = color;
}
The above shader pair will successfully make the terrain darker in color as I
zoom out, but the trees all look completely black no matter what, even if they
originally had varying colors without the shader.
If instead of setting "color" in the frag shader to texture2D() I instead set
it equal to "gl_Color", the shader then works on all the objects in the scene
but I no longer see any remnants of the underlying terrain texture. Based on
this page
http://stackoverflow.com/questions/2552676/change-the-color-of-a-vertex-in-a-vertex-shader
I would have expected that setting color = texture2D(baseTexture,
gl_TexCoord[0].st) * gl_Color would have produced the result I was looking for,
but instead the result is identical to if I leave out * gl_Color.
I think my shader code is very close to being correct and just needs a nudge in
the right direction. Anyone?
Thanks very much in advance.
-Ethan
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=45086#45086
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