layout(lines) in;
layout(triangle_strip, max_vertices = 4) out;

uniform mat4 ProjectionMatrix;
uniform vec2 viewportSize;
uniform int lineThickness = 2;

in vec4 finalColor_geom[];
in vec2 ssPos[];

out vec4 finalColor;

vec2 compute_dir(vec2 v0, vec2 v1)
{
  vec2 dir = normalize(v1 - v0 + 1e-8);
  dir = vec2(-dir.y, dir.x);
  return dir;
}

void main(void)
{
  vec2 t;
  vec2 edge_dir = compute_dir(ssPos[0], ssPos[1]) / viewportSize;

  bool is_persp = (ProjectionMatrix[3][3] == 0.0);

  finalColor = finalColor_geom[0];
  t = edge_dir * (float(lineThickness) * (is_persp ? gl_in[0].gl_Position.w : 1.0));
  gl_Position = gl_in[0].gl_Position + vec4(t, 0.0, 0.0);
  EmitVertex();
  gl_Position = gl_in[0].gl_Position - vec4(t, 0.0, 0.0);
  EmitVertex();

  finalColor = finalColor_geom[1];
  t = edge_dir * (float(lineThickness) * (is_persp ? gl_in[1].gl_Position.w : 1.0));
  gl_Position = gl_in[1].gl_Position + vec4(t, 0.0, 0.0);
  EmitVertex();
  gl_Position = gl_in[1].gl_Position - vec4(t, 0.0, 0.0);
  EmitVertex();
  EndPrimitive();
}