#version 330 core
layout (triangles) in;
layout (triangle_strip) out;

uniform mat4 Model;

in vec2 gtexCoord[];
in vec3 gnormCoord[];
in vec3 gWorldPos[];

out vec2 texCoord;
out vec3 normCoord;
out vec3 WorldPos;

out mat3 TBN;

void main(void)
{
   // Calculate Normal Map stuff

   // Real space triangle
   vec3 p1 = gl_in[0].gl_Position.xyz;
   vec3 p2 = gl_in[1].gl_Position.xyz;
   vec3 p3 = gl_in[2].gl_Position.xyz;

   // Normal texture space triangle
   vec2 uv1 = gtexCoord[0];
   vec2 uv2 = gtexCoord[1];
   vec2 uv3 = gtexCoord[2];

   // Calculate edge translation vectors duv stands for delta uv
   vec3 edge1 = p2 - p1;
   vec3 edge2 = p3 - p1;
   vec2 duv1 = uv2 - uv1;
   vec2 duv2 = uv3 - uv1;

   // Calculation of tangents and bi tangents
   // [ddTxBxTyByTzBz]=1ΔU1ΔV2−ΔU2ΔV1[ΔV2−ΔU2−ΔV1ΔU1][E1xE2xE1yE2yE1zE2z]
   // https://learnopengl.com/Advanced-Lighting/Normal-Mapping

   float f = 1.0 / (duv1.x * duv2.y - duv2.x * duv1.y);

   float tx = f * (duv2.y * edge1.x - duv1.y * edge2.x);
   float ty = f * (duv2.y * edge1.y - duv1.y * edge2.y);
   float tz = f * (duv2.y * edge1.z - duv1.y * edge2.z);

   vec3 tangent = vec3(tx, ty, tz);

   //Calculate TBN
   vec3 T = normalize(vec3(Model * vec4(tangent, 0.0)));
   vec3 N = normalize(vec3(Model * vec4(gnormCoord[0], 0.0)));
   vec3 B = cross(N, T);

   TBN = mat3(T, B, N);

   // send data to Fragment Shader
   gl_Position = gl_in[0].gl_Position;
   texCoord = gtexCoord[0];
   normCoord = gnormCoord[0];
   WorldPos = gWorldPos[0];
   EmitVertex();

   gl_Position = gl_in[1].gl_Position;
   texCoord = gtexCoord[1];
   normCoord = gnormCoord[1];
   WorldPos = gWorldPos[1];
   EmitVertex();

   gl_Position = gl_in[2].gl_Position;
   texCoord = gtexCoord[2];
   normCoord = gnormCoord[2];
   WorldPos = gWorldPos[2];
   EmitVertex();
   EndPrimitive();
};