seascape.sksl

uniform float iTime;
uniform float2 iResolution;
uniform float4 iMouse;

/*
 * "Seascape" by Alexander Alekseev aka TDM - 2014
 * License Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
 * Contact: tdmaav@gmail.com
 * https://www.shadertoy.com/view/Ms2SD1
 */

const int NUM_STEPS = 8;
const float PI = 3.141592;
const float EPSILON = 1e-3;
float EPSILON_NRM() {
  return 0.1 / iResolution.x;
}
// sea
const int ITER_GEOMETRY = 3;
const int ITER_FRAGMENT = 5;
const float SEA_HEIGHT = 0.6;
const float SEA_CHOPPY = 4.0;
const float SEA_SPEED = 0.8;
const float SEA_FREQ = 0.16;
const vec3 SEA_BASE = vec3(0.0, 0.09, 0.18);
const vec3 SEA_WATER_COLOR = vec3(0.8, 0.9, 0.6) * 0.6;
const mat2 octave_m = mat2(1.6, 1.2, -1.2, 1.6);

float SEA_TIME() {
  return (1.0 + iTime * SEA_SPEED);
}

// math
mat3 fromEuler(vec3 ang) {
  vec2 a1 = vec2(sin(ang.x), cos(ang.x));
  vec2 a2 = vec2(sin(ang.y), cos(ang.y));
  vec2 a3 = vec2(sin(ang.z), cos(ang.z));
  mat3 m;
  m[0] = vec3(a1.y * a3.y + a1.x * a2.x * a3.x, a1.y * a2.x * a3.x + a3.y * a1.x, -a2.y * a3.x);
  m[1] = vec3(-a2.y * a1.x, a1.y * a2.y, a2.x);
  m[2] = vec3(a3.y * a1.x * a2.x + a1.y * a3.x, a1.x * a3.x - a1.y * a3.y * a2.x, a2.y * a3.y);
  return m;
}
float hash(vec2 p) {
  float h = dot(p, vec2(127.1, 311.7));
  return fract(sin(h) * 43758.5453123);
}
float noise( in vec2 p) {
  vec2 i = floor(p);
  vec2 f = fract(p);
  vec2 u = f * f * (3.0 - 2.0 * f);
  return -1.0 + 2.0 * mix(mix(hash(i + vec2(0.0, 0.0)),
      hash(i + vec2(1.0, 0.0)), u.x),
    mix(hash(i + vec2(0.0, 1.0)),
      hash(i + vec2(1.0, 1.0)), u.x), u.y);
}

// lighting
float diffuse(vec3 n, vec3 l, float p) {
  return pow(dot(n, l) * 0.4 + 0.6, p);
}
float specular(vec3 n, vec3 l, vec3 e, float s) {
  float nrm = (s + 8.0) / (PI * 8.0);
  return pow(max(dot(reflect(e, n), l), 0.0), s) * nrm;
}

// sky
vec3 getSkyColor(vec3 e) {
  e.y = (max(e.y, 0.0) * 0.8 + 0.2) * 0.8;
  return vec3(pow(1.0 - e.y, 2.0), 1.0 - e.y, 0.6 + (1.0 - e.y) * 0.4) * 1.1;
}

// sea
float sea_octave(vec2 uv, float choppy) {
  uv += noise(uv);
  vec2 wv = 1.0 - abs(sin(uv));
  vec2 swv = abs(cos(uv));
  wv = mix(wv, swv, wv);
  return pow(1.0 - pow(wv.x * wv.y, 0.65), choppy);
}

float map(vec3 p) {
  float freq = SEA_FREQ;
  float amp = SEA_HEIGHT;
  float choppy = SEA_CHOPPY;
  vec2 uv = p.xz;
  uv.x *= 0.75;

  float d, h = 0.0;
  for (int i = 0; i < ITER_GEOMETRY; i++) {
    d = sea_octave((uv + SEA_TIME()) * freq, choppy);
    d += sea_octave((uv - SEA_TIME()) * freq, choppy);
    h += d * amp;
    uv *= octave_m;
    freq *= 1.9;
    amp *= 0.22;
    choppy = mix(choppy, 1.0, 0.2);
  }
  return p.y - h;
}

float map_detailed(vec3 p) {
  float freq = SEA_FREQ;
  float amp = SEA_HEIGHT;
  float choppy = SEA_CHOPPY;
  vec2 uv = p.xz;
  uv.x *= 0.75;

  float d, h = 0.0;
  for (int i = 0; i < ITER_FRAGMENT; i++) {
    d = sea_octave((uv + SEA_TIME()) * freq, choppy);
    d += sea_octave((uv - SEA_TIME()) * freq, choppy);
    h += d * amp;
    uv *= octave_m;
    freq *= 1.9;
    amp *= 0.22;
    choppy = mix(choppy, 1.0, 0.2);
  }
  return p.y - h;
}

vec3 getSeaColor(vec3 p, vec3 n, vec3 l, vec3 eye, vec3 dist) {
  float fresnel = clamp(1.0 - dot(n, -eye), 0.0, 1.0);
  fresnel = pow(fresnel, 3.0) * 0.5;

  vec3 reflected = getSkyColor(reflect(eye, n));
  vec3 refracted = SEA_BASE + diffuse(n, l, 80.0) * SEA_WATER_COLOR * 0.12;

  vec3 color = mix(refracted, reflected, fresnel);

  float atten = max(1.0 - dot(dist, dist) * 0.001, 0.0);
  color += SEA_WATER_COLOR * (p.y - SEA_HEIGHT) * 0.18 * atten;

  color += vec3(specular(n, l, eye, 60.0));

  return color;
}

// tracing
vec3 getNormal(vec3 p, float eps) {
  vec3 n;
  n.y = map_detailed(p);
  n.x = map_detailed(vec3(p.x + eps, p.y, p.z)) - n.y;
  n.z = map_detailed(vec3(p.x, p.y, p.z + eps)) - n.y;
  n.y = eps;
  return normalize(n);
}

float heightMapTracing(vec3 ori, vec3 dir, out vec3 p) {
  float tm = 0.0;
  float tx = 1000.0;
  float hx = map(ori + dir * tx);
  if (hx > 0.0) {
    p = ori + dir * tx;
    return tx;
  }
  float hm = map(ori + dir * tm);
  float tmid = 0.0;
  for (int i = 0; i < NUM_STEPS; i++) {
    tmid = mix(tm, tx, hm / (hm - hx));
    p = ori + dir * tmid;
    float hmid = map(p);
    if (hmid < 0.0) {
      tx = tmid;
      hx = hmid;
    } else {
      tm = tmid;
      hm = hmid;
    }
  }
  return tmid;
}

vec3 getPixel( in vec2 coord, float time) {
  vec2 uv = coord / iResolution.xy;
  uv = uv * 2.0 - 1.0;
  uv.x *= iResolution.x / iResolution.y;

  // ray
  vec3 ang = vec3(sin(time * 3.0) * 0.1, sin(time) * 0.2 + 0.3, time);
  vec3 ori = vec3(0.0, 3.5, time * 5.0);
  vec3 dir = normalize(vec3(uv.xy, -2.0));
  dir.z += length(uv) * 0.14;
  dir = normalize(dir) * fromEuler(ang);

  // tracing
  vec3 p;
  heightMapTracing(ori, dir, p);
  vec3 dist = p - ori;
  vec3 n = getNormal(p, dot(dist, dist) * EPSILON_NRM());
  vec3 light = normalize(vec3(0.0, 1.0, 0.8));

  // color
  return mix(
    getSkyColor(dir),
    getSeaColor(p, n, light, dir, dist),
    pow(smoothstep(0.0, -0.02, dir.y), 0.2));
}

// main
vec4 main(vec2 fragCoord) {
  fragCoord.y = iResolution.y - fragCoord.y;
  fragCoord.x = iResolution.x - fragCoord.x;
  float time = iTime * 0.3 + iMouse.x * 0.01;

  vec3 color = getPixel(fragCoord, time);
  // post
  return (vec4(pow(color, vec3(0.65)), 1.0));
}