#version 430 core
layout (points) in;
layout (triangle_strip, max_vertices = 12) out;

uniform vec2 lightPos;
uniform mat4 worldMat;

vec4 shift (vec4 p)
{ return vec4 (p.xy + (200 * (p.xy-lightPos)), 0 , 1);
}
float isLHS (vec2 startV, vec2 testV)
{
    return sign( -startV.x * testV.y + startV.y * testV.x);
}
void emitLine (vec2 pa)
{
    gl_Position = vec4 (pa, 0, 1);
    EmitVertex();
    gl_Position = shift (vec4 (pa,0,1)); //vec4 (pa + (200 * (pa - lightPos)), 0 , 1);
    EmitVertex();
}

mat4 perspective =  
    mat4 (1,0,0,0
         ,0,1,0,0
         ,0,0,1,1
         ,0,0,0,1
         ) ;
// construct a box with opening on bottom face

void main()
{
vec4 p1 = worldMat * vec4 (gl_in[0].gl_Position.xy,0,1);
vec4 p2 = worldMat * vec4 (gl_in[0].gl_Position.zw,0,1);
if (isLHS (p1.xy - lightPos, p2.xy - lightPos) < 0)
{
vec4 p3 = vec4 (p1.xy,-0.5,1);
vec4 p4 = vec4 (p2.xy,-0.5,1);
vec4 p5 = shift(p1);
vec4 p6 = shift(p2);
vec4 p7 = vec4 (p6.xy,-0.5,1);
vec4 p8 = vec4 (p5.xy,-0.5,1);
  gl_Position = perspective * p4; EmitVertex();
  gl_Position = perspective * p3; EmitVertex();
  gl_Position = perspective * p7; EmitVertex();
  gl_Position = perspective * p8; EmitVertex();
  gl_Position = perspective * p5; EmitVertex();
  gl_Position = perspective * p3; EmitVertex();
  gl_Position = perspective * p1; EmitVertex();
  gl_Position = perspective * p4; EmitVertex();
  gl_Position = perspective * p2; EmitVertex();
  gl_Position = perspective * p7; EmitVertex();
  gl_Position = perspective * p6; EmitVertex();
  gl_Position = perspective * p5; EmitVertex();
  EndPrimitive();
} else {}
}

//  //  void main()
//  //  {
//  //    vec4 frontL4 = worldMat * vec4(gl_in[0].gl_Position.xy, 0 ,1);
//  //    vec4 frontR4 = worldMat * vec4(gl_in[0].gl_Position.zw, 0 ,1);
//  //    vec2 frontL = frontL4.xy;
//  //    vec2 frontR = frontR4.xy;
//  //  
//  //      emitLine (frontR);
//  //      emitLine (frontL);
//  //    EndPrimitive();
//  //  }
//  gl_Position = perspective * worldMat * p4; EmitVertex();
//  gl_Position = perspective * worldMat * p3; EmitVertex();
//  gl_Position = perspective * worldMat * p7; EmitVertex();
//  gl_Position = perspective * worldMat * p8; EmitVertex();
//  gl_Position = perspective * worldMat * p5; EmitVertex();
//  gl_Position = perspective * worldMat * p3; EmitVertex();
//  gl_Position = perspective * worldMat * p1; EmitVertex();
//  gl_Position = perspective * worldMat * p4; EmitVertex();
//  gl_Position = perspective * worldMat * p2; EmitVertex();
//  gl_Position = perspective * worldMat * p7; EmitVertex();
//  gl_Position = perspective * worldMat * p6; EmitVertex();
//  gl_Position = perspective * worldMat * p5; EmitVertex();