Reverse Light Geometry Shader

Geometry Shader

/***********************************************
 Geometry shader to convert lines into triangle strips
 Memo Akten
 www.memo.tv
 
 modified by: STEADY

************************************************/

#version 120
#extension GL_EXT_geometry_shader4 : enable

uniform float thickness;
uniform vec3 lightDir;
uniform vec4 currentColor;
//uniform vec4 brighten = vec4(1.0,1.0,1.0, 0.9);

void main() {
	vec3 p0 = gl_PositionIn[0].xyz;
	vec3 p1 = gl_PositionIn[1].xyz;
	vec3 up = vec3(0, 0, 1);	// arbitrary up vector
	vec4 brighten = vec4(1.0,1.0,1.0, 0.8);
    
	vec3 dir = normalize(p1 - p0);			// normalized direction vector from p0 to p1
	vec3 right = normalize(cross(dir, up));	// right vector
	vec3 norm = cross(right, dir);
	float fColMult = abs(dot(norm, lightDir));
	vec4 colMult = vec4(fColMult, fColMult, fColMult, 1.0);

	right *= thickness;
	
	gl_Position = gl_ModelViewProjectionMatrix * vec4(p0 - right*1.0, 1.0);
    //gl_FrontColor = gl_FrontColorIn[0] * colMult;
    gl_FrontColor = currentColor;
	EmitVertex();
	
	gl_Position = gl_ModelViewProjectionMatrix * vec4(p0 + right*1.0, 1.0);
	//gl_FrontColor = gl_FrontColorIn[0] * colMult;
    gl_FrontColor = currentColor;
	EmitVertex();
	
	gl_Position = gl_ModelViewProjectionMatrix * vec4(p1 - right*3.0, 1.0);
	//gl_FrontColor = gl_FrontColorIn[1] * colMult;
    gl_FrontColor = brighten;
    EmitVertex();

	gl_Position = gl_ModelViewProjectionMatrix * vec4(p1 + right*3.0, 1.0);
	//gl_FrontColor = gl_FrontColorIn[1] * colMult;
    gl_FrontColor = brighten;	
    EmitVertex();

}