#version 430 core
layout (points) in;
layout (triangle_strip, max_vertices = 4) out;
layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
uniform vec3 lightPos;
uniform vec2 radLum;
out vec3 dField;
out float lum;
float isLHS (vec2 startV, vec2 testV)
{
    return sign( -startV.x * testV.y + startV.y * testV.x);
}
vec4 shiftCloser (vec4 v)
{ return vec4 (v.xy , v.z-0.0001 , v.w) ; }
void main()
{
vec4 p1 = vec4 (gl_in[0].gl_Position.xy,0.1,1);
vec4 p2 = vec4 (gl_in[0].gl_Position.zw,0.1,1);
if (isLHS (p1.xy - lightPos.xy, p2.xy - lightPos.xy) < 0)
{
    lum = radLum.y;
    float rad = radLum.x;

    vec4 p3 = vec4 (p1.xy,-0.3,1);
    vec4 p4 = vec4 (p2.xy,-0.3,1);

    vec2 d1 = p1.xy - lightPos.xy;
    vec2 d2 = p2.xy - lightPos.xy;
    
    vec4 a1 = shiftCloser( theMat * p1 );
    vec4 a2 = shiftCloser( theMat * p2 );
    vec4 a3 = shiftCloser( theMat * p3 );
    vec4 a4 = shiftCloser( theMat * p4 );
    
    dField = vec3( d1.x/rad, d1.y/rad, 100.0/rad);
    gl_Position = a1; 
    EmitVertex();
    dField = vec3( d1.x/rad, d1.y/rad, -300.0/rad);
    gl_Position = a3; 
    EmitVertex();
    dField = vec3( d2.x/rad, d2.y/rad, 100.0/rad);
    gl_Position = a2; 
    EmitVertex();
    dField = vec3( d2.x/rad, d2.y/rad, -300.0/rad);
    gl_Position = a4; 
    EmitVertex();
    
    EndPrimitive();
} else {}
}