#version 450 core
layout (points) in;
layout (triangle_strip, max_vertices = 4) out;
layout (std140, binding = 0) uniform TheMat { mat4 theMat; } ;
in vec4 vColor [];
out vec4 gColor;
out vec4 gPos;
// consider using isLHS to check if the wall is facing the center
// this needs the view from point
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 a1 = theMat * p1;
  vec4 a2 = theMat * p2;
//  if (0 > isLHS (a1.xy - a2.xy, a1.xy - "viewFromPoint")) {
    vec4 p3 = vec4 (p1.xy,5000,1); //note the random z value, used for GL_DEPTH_CLAMP
    vec4 p4 = vec4 (p2.xy,5000,1);
    vec4 a3 = theMat * p3;
    vec4 a4 = theMat * p4;
    gPos = p1;gl_Position = a1; EmitVertex();
    gPos = p3;gl_Position = a3; EmitVertex();
    gPos = p2;gl_Position = a2; EmitVertex();
    gPos = p4;gl_Position = a4; EmitVertex();
    EndPrimitive();
//  }
}