#version 430 core
layout (points) in;
layout (triangle_strip, max_vertices = 4) out;

in vec4 vColor [];
out vec4 gColor;
out vec2 tPos;

uniform mat4 perpMat;

// consider using isLHS to check if the wall is facing the center
float isLHS (vec2 startV, vec2 testV)
{
    return sign( -startV.x * testV.y + startV.y * testV.x);
}

void main()
{
    gColor = vColor[0];

vec4 p1 = vec4 (gl_in[0].gl_Position.xy,0,1);
vec4 p2 = vec4 (gl_in[0].gl_Position.zw,0,1);
vec4 p3 = vec4 (p1.xy,-0.5,1);
vec4 p4 = vec4 (p2.xy,-0.5,1);

vec4 a1 = perpMat * p1;
vec4 a2 = perpMat * p2;
vec4 a3 = perpMat * p3;
vec4 a4 = perpMat * p4;

  tPos = vec2 ( 1,-1) ; gl_Position = a1; EmitVertex();
  tPos = vec2 ( 1, 1) ; gl_Position = a3; EmitVertex();
  tPos = vec2 (-1,-1) ; gl_Position = a2; EmitVertex();
  tPos = vec2 (-1, 1) ; gl_Position = a4; EmitVertex();
  EndPrimitive();
}