I would like to use a shader on a gl.model. 

There 's already fog effect apply to this model. 

And when I tell the shader object to apply its shade, the fog (and light) effect disappears.

Has anyone know the way to avoid this issue ? 

I would like to use a shader on a gl.model. 
There 's already fog effect apply to this model. 
And when I tell the shader object to apply its shade, the fog (and light) effect disappears.
Here's the patch which shows the thing: 

Has anyone know the way to avoid this issue ? 
Thx.

gl-shader-make-the-fog-effect-disappear

fog must be computed in the fragment shader.

relevant code from the orange book for linear fog computation with clamping:

gl_FogFragCoord = gl_FogCoord;
float fog = (gl_Fog.end - gl_FogFragCoord)) * gl_Fog.scale;
fog = clamp(fog, 0.0, 1.0);
//Applying fog to compute final color value
color = mix(vec3(gl_Fog.color), color, fog);


I must have done something wrong in the jxs ' structure:

ERROR: 0:17: 'gl_FogCoord' : undeclared identifier 

ERROR: 0:17: 'assign' : l-value required "gl_FogFragCoord" (can't modify a varying)

ERROR: 0:18: '=' : cannot convert from 'float' to '4-component vector of float'

ERROR: 0:18: ')' : syntax error syntax error

ERROR: Parser found no code to compile in source strings.

• error: jit.gl.shader: GLSL program failed to compile.

I must have done something wrong in the jxs ' structure: 

• error: -- START GLSL INFO LOG: fp --
ERROR: 0:17: 'gl_FogCoord' : undeclared identifier 
ERROR: 0:17: 'assign' :  l-value required "gl_FogFragCoord" (can't modify a varying)
ERROR: 0:18: '=' :  cannot convert from 'float' to '4-component vector of float'
ERROR: 0:18: ')' : syntax error syntax error
ERROR: Parser found no code to compile in source strings.
• error: -- END GLSL INFO LOG: fp --
• error: jit.gl.shader: GLSL program failed to compile.


whoops, it looks like fog should be a float, not a vec4.

i just posted some snippets from the book without testing, but the general idea is there.

    vec4 v0 = texture2DRect(texture, texcoord0);

    v0 = (v0*inscale)+inoffset;    

    gl_FragColor = (result*outscale)+outoffset;

    float fog = (gl_Fog.end - gl_FogFragCoord)) * gl_Fog.scale;

    vec4 color = mix(vec3(gl_Fog.color), color, fog);

• error: jit_xml_document: error reading file at byte offset 1303 / not well-formed (invalid token)

• error: jit.gl.shader: error reading shader xml file 'Macintosh HD:/Users/adrienfontaine/Desktop/op.abs.jxs'

		Input scale
		Input offset
		Output scale
		Output offset

void main( void )
{
	vec4 v0 = texture2DRect(texture, texcoord0);

	v0 = (v0*inscale)+inoffset;	
	vec4 result = abs(v0);
	gl_FragColor = (result*outscale)+outoffset;
	float fog = (gl_Fog.end - gl_FogFragCoord)) * gl_Fog.scale;
	fog = clamp(fog, 0.0, 1.0);
	vec4 color = mix(vec3(gl_Fog.color), color, fog);
}
]]>

 • error: jit_xml_document: error reading file at byte offset 1303 / not well-formed (invalid token)
• error: line (48): >
• error: jit.gl.shader: error reading shader xml file 'Macintosh HD:/Users/adrienfontaine/Desktop/op.abs.jxs'


I am searching in a red book, but can't find anything about that !

I don't know what the shader you posted is supposed to do, but if you're trying to have fog with a shader, here's an example:

--------------------------------------
--------------------------------------
mat.phong.1.light.fog.falloff.jxs
--------------------------------------

		Ambient Multiplier
		Diffuse Multiplier
		Light Falloff Rate
		Fog Density
		Fog Density
		Fog Color
		Specular Multiplier
		Specularity Adjustment

Thank you so much !! 
It Works just fine.

Any chance to have a copy of your shader mat.phong.1.light.fog.falloff.jxs ?

[EDIT] Thanks to archive.org !!! https://web.archive.org/web/20130322030458/http://cycling74.com/forums/topic.php?id=44686 

mat.phong.1.light.fog.falloff.jxs

[EDIT] Thanks to archive.org !!!  https://web.archive.org/web/20130322030458/http://cycling74.com/forums/topic.php?id=44686 



gl.shader make the fog effect disappear