// tessellation evaluation shader
#version 450 core

layout (quads, fractional_even_spacing, ccw) in;

layout(std430, binding = 1) readonly buffer positions_buffer 
{
	mat4 model_matrix[];
};

layout(binding = 0) uniform uniform_per_frame
{	
	mat4 view;
	mat4 proj;	
	vec3 viewer_pos;	
	uint light_count;
} ubo_per_frame;

// received from Tessellation Control Shader - all texture coordinates for the patch vertices
// varying input from vertex shader

layout (location=0) in TC_OUT
{
	vec2 vsUV;
	vec4 vsWorldPos;
	vec3 vsNormal;
	vec3 vsBiTangent;
	vec3 vsTangent;
	mat3 vsTBN;
	flat uint vsChunkID;
	flat uint vsMaterialID;
}te_in[];

layout (location=0) out TE_OUT
{
	vec2 vsUV;
	vec4 vsWorldPos;
	vec3 vsNormal;
	vec3 vsBiTangent;
	vec3 vsTangent;
	mat3 vsTBN;
	flat uint vsChunkID;
	flat uint vsMaterialID;
}te_out;

void main()
{
    // get patch coordinate
    te_out.vsUV.x = gl_TessCoord.x;
    te_out.vsUV.y = gl_TessCoord.y;

    // ----------------------------------------------------------------------
    // retrieve control point texture coordinates
    vec2 t00 = te_in[0].vsUV;
    vec2 t01 = te_in[1].vsUV;
    vec2 t10 = te_in[2].vsUV;
    vec2 t11 = te_in[3].vsUV;

//    t00|t10
//    -------
//    t10|t11

    // ----------------------------------------------------------------------
    // retrieve control point position coordinates
    vec4 p00 = gl_in[0].gl_Position;
    vec4 p01 = gl_in[1].gl_Position;
    vec4 p10 = gl_in[2].gl_Position;
    vec4 p11 = gl_in[3].gl_Position;



    // compute patch surface normal
    vec4 uVec = p01 - p00;
    vec4 vVec = p10 - p00;
    vec4 normal = normalize( vec4(cross(uVec.xyz, vVec.xyz), 1));

    te_out.vsNormal = normal.xyz;
    // bilinearly interpolate position coordinate across patch
    vec4 p0 = (p01 - p00) *  te_out.vsUV.x + p00;
    vec4 p1 = (p11 - p10) *  te_out.vsUV.x + p10;
    vec4 p = (p1 - p0) *  te_out.vsUV.y + p0;
    
    // displace point along normal
   // p += -normal * height;
   //height = 0;
    
    //p[3] = 1;
    // ----------------------------------------------------------------------
    // output patch point position in clip space

    mat4 model = model_matrix[te_in[0].vsChunkID];
	mat4 view = ubo_per_frame.view;
	mat4 proj = ubo_per_frame.proj;
    gl_Position = proj * view * model * p;

   
    
}