Test Scene :
http://img819.imageshack.us/img819/9569/shotone.png
http://img862.imageshack.us/img862/1044/shottwo.png
http://img7.imageshack.us/img7/8624/shotthree.png
Performance:
not sure. When doing the above tests, the frame rate did change between light on or off.
Some Possible Uses :
Highlighting objects :: door knobs, chests, weapons ect… good for ‘picking’
works well in cartoon looking scenes to brighten edges
can be used for velvet effects.
great for xray effects
I have simply added a few lines to standard Lighting shader, so I will try and show what I did. Im not really sure the best way to share my code so I will just show all the changes I have made as best I can, and if someone could please halp advise me the best way to go from here 
I’m sorry if this is in the wrong place or is unclear.
Common/MatDefs/Light/Lighting.j3md
[patch]
// the env map is a spheremap and not a cube map
Boolean EnvMapAsSphereMap
+
- Color RimLighting;
+
}
Technique {
[/patch]
[patch]
USE_REFLECTION : EnvMap
SPHERE_MAP : SphereMap
+
-
RIM_LIGHTING : RimLighting<br />
}
}
[/patch]
Common/MatDefs/Light/Lighting.vertfrag
[patch]
uniform ENVMAP m_EnvMap;
#endif
+
- uniform vec4 m_RimLighting;
float tangDot(in vec3 v1, in vec3 v2){
[/patch]
[patch]
#endif
gl_FragColor.a = alpha;
+
-
#ifdef RIM_LIGHTING
+
- vec4 rim = pow( 1.0 - dot( normal, vViewDir.xyz ), 1.5 ) * m_RimLighting * m_RimLighting.w;
- rim.a = 0.0;
+
- gl_FragColor += rim*diffuseColor;
-
#endif
}
[/patch]
Usage
usage is pretty simple …
[java]float red = 0.0f;
float blue = 0.0f;
float green = 1.0f;
float power = 0.5f;
mat.setColor(“RimLighting”, new ColorRGBA(red,green,blue,power));[/java]
The RimShader is a Color, alhpa is used as the “power”, the higher the power the greater the effect. power must be > 0.
There is room to add some more customization to the appears by passing in a bias and additional power. There is probably plenty of room for optimization as well.