#version 450
#extension GL_EXT_buffer_reference : require

#include "hex_common.glsl"

#define PI 3.1415926535897932384626433832795
const float w = 0.5;
const float x = 0.75;
const float z = sqrt(3.0)/4.0;

const vec4 vertices[] = {
  vec4(0,             0, 0,             1),
  vec4(w*cos(0*PI/3), 0, w*sin(0*PI/3), 1),
  vec4(w*cos(1*PI/3), 0, w*sin(1*PI/3), 1),
  vec4(w*cos(2*PI/3), 0, w*sin(2*PI/3), 1),
  vec4(w*cos(3*PI/3), 0, w*sin(3*PI/3), 1),
  vec4(w*cos(4*PI/3), 0, w*sin(4*PI/3), 1),
  vec4(w*cos(5*PI/3), 0, w*sin(5*PI/3), 1),
};

const uint indices[] = {
  0, 2, 1,
  0, 3, 2,
  0, 4, 3,
  0, 5, 4,
  0, 6, 5,
  0, 1, 6,
};

const vec4 starts[] = {
  vec4( 0, 0,  2*z, 0),
  vec4(-x, 0,    z, 0),
  vec4(-x, 0,   -z, 0),
  vec4( 0, 0, -2*z, 0),
  vec4( x, 0,   -z, 0),
  vec4( x, 0,    z, 0),
};

const vec4 direction[] = {
  vec4(-x, 0,   -z, 0),
  vec4( 0, 0, -2*z, 0),
  vec4( x, 0,   -z, 0),
  vec4( x, 0,    z, 0),
  vec4( 0, 0,  2*z, 0),
  vec4(-x, 0,    z, 0),
};

void main() {
  uint radius = 0;
  uint ring = 0;
  uint side = 0;
  uint hex = 0;
  if(gl_InstanceIndex != 0) {
    radius = uint(floor(0.5 + sqrt(12*gl_InstanceIndex-3)/6));
    ring = gl_InstanceIndex - (3*radius*radius - 3*radius + 1);
    side = uint(floor(ring/(radius)));
    hex = ring - (radius*side);
  }

  // Calculate position based on radius/ring/side/hex
  vec4 position = vertices[indices[gl_VertexIndex]] + (starts[side]*radius) + (direction[side]*hex);

  gl_Position = pc.context.proj * pc.context.view * position;
}