#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 vec2 tPos;
out vec4 gPos;
out vec4 gNorm;
// 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,100,1);
  vec4 p4 = vec4 (p2.xy,100,1);
  vec2 d = vec2(p1.xy - p2.xy);
  vec4 norm = vec4( d.y, -d.x, 0, 1);
  gNorm = p1 - norm;
  gPos = p1; tPos = vec2 ( 1,-1) ; gl_Position = vec4(theMat * p1); EmitVertex();
  gNorm = p1 - norm;
  gPos = p3; tPos = vec2 ( 1, 1) ; gl_Position = vec4(theMat * p3); EmitVertex();
  gNorm = p1 - norm;
  gPos = p2; tPos = vec2 (-1,-1) ; gl_Position = vec4(theMat * p2); EmitVertex();
  gNorm = p1 - norm;
  gPos = p4; tPos = vec2 (-1, 1) ; gl_Position = vec4(theMat * p4); EmitVertex();
  EndPrimitive();
}