code:

uniform float scale_factor; 
uniform float gauss_a; 
uniform float gauss_b; 
uniform float gauss_c; 
varying vec4 colorz; 
void main( void ) 
{ 
    gl_FrontColor = gl_Color;
    float e = 2.71828;
    float x = gl_FrontColor.w;
    float exponent = x - gauss_b; 
    exponent *= exponent;
    exponent /= -2 * ( gauss_c * gauss_c );
    gl_FrontColor.w = scale_factor * gauss_a * exp( exponent );
    colorz = gl_FrontColor; 
    gl_Position = ftransform();
}