#version 410 core

uniform float fGlobalTime; // in seconds
uniform vec2 v2Resolution; // viewport resolution (in pixels)

uniform sampler1D texFFT; // towards 0.0 is bass / lower freq, towards 1.0 is higher / treble freq
uniform sampler1D texFFTSmoothed; // this one has longer falloff and less harsh transients
uniform sampler2D texBirds;
uniform sampler2D texGrass;
uniform sampler2D texNormal;
uniform sampler2D texPerlin;
uniform sampler2D texTiles;
uniform sampler2D texZigZag;

out vec4 out_color;

const float PI = 3.14159;

float fbx(vec3 p)
{
  return texture(texPerlin, vec2(p.y + fGlobalTime, p.x)).x;
}

float scene(vec3 p)
{
  float displace = sin(p.x + fGlobalTime)*sin(p.y)*sin(p.z);
  return fbx(p) + displace;
}

vec3 normal(vec3 p)
{
  vec3 e = vec3(0.01,0,0);
  vec3 normal;
  normal.x = scene(p-e.xyz) + scene(p+e.xyz);
  normal.y = scene(p-e.yxz) + scene(p+e.yxz);
  normal.z = scene(p-e.yzx) + scene(p+e.yzx);
  return normalize(normal);
}

void main()
{
  vec2 uv = vec2((gl_FragCoord.x - 0.5 * v2Resolution.x) / v2Resolution.y,
              (gl_FragCoord.y - 0.5 * v2Resolution.y) / v2Resolution.y);

  vec3 rayO = vec3(0,0,2.0);
  vec3 rayD = vec3(uv, -1.0);
  float t = 0;
  vec3 color = vec3(0,0,0);
  for(int i = 0;i != 32;++i)
  {
     vec3 p = rayO + rayD * t;
     float d = scene(p);
     if(d < 0.05)
      {
        vec3 norm = normal(p);
        color = vec3(0.4,0.9,1.0) * dot(norm, vec3(0.33));
      }

    t += d;
  }

  color += pow(color, vec3(2.0));

  // gamma adjust
  out_color.rgb = color;//pow(o, vec3(1/2.2));
}