#version 330

precision mediump float;

float EPS = 0.0001;
float PI = 3.14159265359;
float FLT_MAX = 900.;

uniform float u_time;
uniform vec2 u_resolution;

layout(location = 1) out vec4 my_fragColor;

const int maxIterations = 64;
const float stepScale = 1.;
const float stopThreshold = .005;

float fov = .6;
float nearClip = 0.;
float farClip = 80.;

struct Light {
  vec3 position;
  float intensity;
  vec3 color;
};
    
struct Surface {
  float dist;
  vec3 position;
  vec3 baseColor;
  vec3 normal;
  vec3 emissiveColor;
};
    
struct Hit {
  Surface surface;
  Surface near;
};
    
float saturate(float s) {
  return clamp(s, 0., 1.);
}

float distanceToLine(vec3 origin, vec3 dir, vec3 point) {
	vec3 pointToOrigin = point - origin;
    float pointToOriginLength = length(pointToOrigin);
    vec3 pointToOriginNorm = normalize(pointToOrigin);
    float theta = dot(dir, pointToOriginNorm);
    return pointToOriginLength * sqrt(1. - theta * theta);
}

mat4 scale(vec3 s) {
    mat4 m = mat4(
    s.x, 0., 0., 0.,
    0., s.y, 0., 0.,
    0., 0., s.z, 0.,
    0., 0., 0., 1.
  );
  return inverse(m);
}

mat4 rotateX(float angle) {
  return inverse(mat4(
    1., 0., 0., 0.,
    0., cos(angle), -sin(angle), 0.,
    0., sin(angle), cos(angle), 0.,
    0., 0., 0., 1.
  ));
}

mat4 rotateY(float angle) {
  return inverse(mat4(
    cos(angle), 0., sin(angle), 0.,
    0., 1., 0., 0.,
    -sin(angle), 0., cos(angle), 0.,
    0., 0., 0., 1.
  ));
}

mat4 rotateZ(float angle) {
  return inverse(mat4(
    cos(angle), -sin(angle), 0., 0.,
    sin(angle), cos(angle), 0., 0.,
    0., 0., 1., 0.,
    0., 0., 0., 1.
  ));
}

mat4 translate(vec3 p) {
  return inverse(mat4(
    1., 0., 0., p.x,
    0., 1., 0., p.y,
    0., 0., 1., p.z,
    0., 0., 0., 1.
  ));
}

float sphere(vec3 p, float size) {
  return length(p) - size;
}

float box(vec3 p, vec3 size) {
  vec3 d = abs(p) - size;
  return length(max(d, 0.)) + min(max(d.x, max(d.y, d.z)), 0.);
}

float tube2(vec2 p, float size) {
  return length(p) - size;
}

float box2(vec2 p, float size) {
  return length(max(abs(p) - size, 0.));
}

float cylindar(vec3 p, vec3 c) {
  return length(p.xz - c.xy) - c.z;
}

float displacement(vec3 p, vec3 power) {
  return sin(power.x * p.x) * sin(power.y * p.y) * sin(power.z * p.z);
}

vec3 repeat(vec3 p, float c) {
  return mod(p, c) - c * .5;
}

float smin(float a, float b, float k) {
  float res = exp(-k * a) + exp(-k * b);
  return -log(res) / k;
}

float scene(vec3 p) {
  vec3 _p = p;

  _p = (vec4(_p, 1.)).xyz;
    
  return min(
    sphere((vec4(p, 1.) * translate(vec3(-.7, 0., 0.))).xyz, .5),
    box((vec4(p, 1.) * translate(vec3(.7, 0., 0))).xyz, vec3(.45))
  );
}

float calcAO(vec3 p, vec3 n) {
  float k = 1.;
  float occ = 0.;
  for(int i = 0; i < 5; i++) {
    float len = .15 * (float(i) + 1.);
    float distance = scene(n * len + p);
    occ += (len - distance) * k;
    k *= .5;
  }
  return clamp(1. - occ, 0., 1.);
}

vec3 getNormal(vec3 p) {
  const float e = EPS;
  return normalize(vec3(
    scene(p + vec3(e,   0.0, 0.0)) - scene(p + vec3(-e,  0.0, 0.0)),
    scene(p + vec3(0.0,   e, 0.0)) - scene(p + vec3(0.0,  -e, 0.0)),
    scene(p + vec3(0.0, 0.0,   e)) - scene(p + vec3(0.0, 0.0,  -e))
  ));
}

Surface near(Surface needle, Surface target) {
  if(needle.dist < 0. || needle.dist < target.dist) {
    return needle;
  }
  return target;
}

Hit rayMarching(vec3 origin, vec3 dir, float start, float end) {
  Surface cs;  // current surface
  cs.dist = -1.;
    
  Surface ns; // near surface
  ns.dist = FLT_MAX;
    
  Hit hit;

  float sceneDist = 0.;
  float rayDepth = start;

  for(int i = 0; i < maxIterations; i++) {
    sceneDist = scene(origin + dir * rayDepth);
      
    // cache near distance
    if(sceneDist < ns.dist) {
      ns.dist = sceneDist;
    }

    if((sceneDist < stopThreshold) || (rayDepth >= end)) {
     break;
    }
    rayDepth += sceneDist * stepScale;
    cs.dist = rayDepth;
  }
    
  if (sceneDist >= stopThreshold) {
    rayDepth = end;
  }
    
  cs.dist = rayDepth;
  hit.surface = cs;
  hit.near = ns;

  return hit;
}

float getSpecular(vec3 position, vec3 normal, Light light, float diffuse, vec3 cameraPos) {
  vec3 lightDir = light.position - position;
  vec3 ref = reflect(-normalize(lightDir), normal);
  float specular = 0.;
  if(diffuse > 0.) {
    specular = max(0., dot(ref, normalize(cameraPos - normal)));
    float specularPower = 32.;
    specular = pow(specular, specularPower) * light.intensity;
  }
  return specular;
}

vec3 lighting(Surface surface, vec3 cameraPos) {
  vec3 position = surface.position;

  vec3 color = vec3(0.);
  vec3 sceneColor = vec3(0.);
  vec3 normal = getNormal(position);

  vec3 objColor = vec3(.4, .4, .4);
  vec3 specularColor = vec3(.6, .6, .6);

  Light directionalLight;
  directionalLight.position = vec3(5., 5., 5.);
  directionalLight.intensity = .8;
  directionalLight.color = vec3(.4, .4, .4);

  Light pointLight;
  pointLight.position = vec3(5., 5., 5.);
  pointLight.intensity = .8;
  pointLight.color = vec3(.5, .5, .5);

  Light ambientLight;
  ambientLight.color = vec3(.1, .1, .1);
  ambientLight.intensity = .3;
    
  // directional light
  float dDiffuse = max(0., dot(normal, normalize(directionalLight.position)));
  dDiffuse *= directionalLight.intensity;
  vec3 dDiffuseColor = dDiffuse * directionalLight.color * objColor;
  float dSpecular = getSpecular(position, normal, directionalLight, dDiffuse, cameraPos);
  vec3 dSpecularColor = dSpecular * specularColor;

  // point light
  vec3 pLightDir = pointLight.position - position;
  float pDiffuse = max(0., dot(normal, normalize(pLightDir)));
  vec3 pDiffuseColor = pDiffuse * pointLight.color * objColor;
  float d = distance(pointLight.position, position);
  vec3 k = vec3(.05, .9, .06);
  float attenuation = 1. / (k.x + (k.y * d) + (k.z * d * d));
  pDiffuse *= pointLight.intensity;
  pDiffuse *= attenuation;
  float pSpecular = getSpecular(position, normal, pointLight, pDiffuse, cameraPos);
  pSpecular *= attenuation;
  vec3 pSpecularColor = pSpecular * specularColor;
    
  // ambient
  vec3 ambientColor = ambientLight.color * ambientLight.intensity * objColor;
  float ao = calcAO(position, normal);

  vec3 diffuse = dDiffuseColor + pDiffuseColor;
  vec3 specular = dSpecularColor + pSpecularColor;
  vec3 ambient = ambientColor * ao;

  // color += objColor * diffuse + specular + ambient * ao;
  color += objColor * diffuse + ambient * ao;
    
  return color;
}

vec3 emissiveLight(Light light, Surface surface, vec3 rayOrigin, vec3 rayDirection) {
  vec3 eyeDirection = rayOrigin + rayDirection;
  
  float lightEmissive = pow(distanceToLine(eyeDirection, rayDirection, light.position) + .95, -2.);

  float c = dot(surface.normal, normalize(light.position - surface.position));
  c = clamp(c, 0., 1.);
  float em = 0.;

  em = c + (1. - c) * step(farClip, surface.dist);

  return lightEmissive * light.color * light.intensity * em;  
}

vec3 emissiveLighting(Surface surface, vec3 rayOrigin, vec3 rayDirection) {
  vec3 eyeDirection = rayOrigin + rayDirection;
  vec3 normal = surface.normal;

  Light pointLightRed;
  pointLightRed.color = vec3(1., .1, .1);
  pointLightRed.intensity = 1.;
  pointLightRed.position = vec3(cos(u_time * 1.4) * 2., sin(u_time * 1.4) * 2., 0.);
  
  Light pointLightGreen;
  pointLightGreen.color = vec3(.1, 1., .1);
  pointLightGreen.intensity = 1.;
  pointLightGreen.position = vec3(cos(u_time * 1.6) * 2., 0., sin(u_time * 1.6) * 2.);

  Light pointLightBlue;
  pointLightBlue.color = vec3(.1, .1, 1.);
  pointLightBlue.intensity = 1.;
  pointLightBlue.position = vec3(0., sin(u_time * 1.8) * 2., cos(u_time * 1.8) * 2.);    
    
    
  vec3 color = vec3(0.);
  color += emissiveLight(pointLightRed, surface, rayOrigin, rayDirection);
  color += emissiveLight(pointLightGreen, surface, rayOrigin, rayDirection);
  color += emissiveLight(pointLightBlue, surface, rayOrigin, rayDirection);

  return color;    
}


void main() {
  /*vec2 aspect = vec2(u_resolution.x / u_resolution.y, 1.);
  vec2 screenCoord = (2. * gl_FragCoord.xy / u_resolution.xy - 1.) * aspect;
  // vec2 mouse = u_mouse.xy / u_resolution.xy - .5;
  
  // camera settings
  vec3 lookAt = vec3(0., 0., 0.);
  vec3 cameraPos = vec3(0.,0., 5.);

  // camera vectors
  vec3 forward = normalize(lookAt - cameraPos);
  vec3 right = normalize(cross(forward, vec3(0., 1., 0.)));
  vec3 up = normalize(cross(right, forward));        

  // raymarch
  vec3 rayOrigin = cameraPos;
  vec3 rayDirection = normalize(forward + fov * screenCoord.x * right + fov * screenCoord.y * up);
  Hit hit = rayMarching(rayOrigin, rayDirection, nearClip, farClip);
  Surface surface = hit.surface;
  Surface near = hit.near;

  surface.position = rayOrigin + rayDirection * surface.dist;
    
  // color
  vec3 sceneColor = vec3(0.);
    
  // no hit or too far
  if(surface.dist >= farClip) {
    vec3 bgColor = vec3(0.);
    sceneColor = bgColor;
  } else {
    sceneColor += lighting(surface, cameraPos);
  }

  surface.normal = getNormal(surface.position);
  sceneColor += emissiveLighting(surface, rayOrigin, rayDirection);
*/

 // my_fragColor = vec4(sceneColor, 1.);
 my_fragColor = vec4(vec3(0., 1., 0.), 1.);
}