/*{
  "DESCRIPTION": "Ember-tinted smoke ribbons with layered emitters, buoyant curl, and persistent afterimages.",
  "INPUTS": [
    { "NAME": "flowSpeed", "TYPE": "float", "DEFAULT": 1.15, "MIN": 0.0, "MAX": 2.5 },
    { "NAME": "turbulence", "TYPE": "float", "DEFAULT": 1.25, "MIN": 0.0, "MAX": 2.5 },
    { "NAME": "lift", "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "dissipation", "TYPE": "float", "DEFAULT": 0.9986, "MIN": 0.97, "MAX": 0.9998 },
    { "NAME": "emberRate", "TYPE": "float", "DEFAULT": 0.72, "MIN": 0.0, "MAX": 1.5 },
    { "NAME": "emitterSize", "TYPE": "float", "DEFAULT": 0.052, "MIN": 0.015, "MAX": 0.14 },
    { "NAME": "smokeColor", "TYPE": "color", "DEFAULT": [0.34, 0.58, 1.0, 1.0] }
  ],
  "PASSES": [
    { "TARGET": "smokeBuffer", "PERSISTENT": true, "FLOAT": true },
    {}
  ]
}*/

#define TAU 6.28318530718

vec2 velocityField(vec2 uv, float t) {
  vec2 p = uv - 0.5;
  p.x *= RENDERSIZE.x / RENDERSIZE.y;
  float r = length(p);
  float angle = atan(p.y, p.x);
  vec2 v = vec2(sin(TAU * uv.x), -cos(TAU * uv.y));
  v += 0.44 * vec2(sin(TAU * (2.0 * uv.y + t * 0.055)),
                    cos(TAU * (2.0 * uv.x - t * 0.071)));
  v += 0.30 * vec2(cos(angle * 3.0 - t * 0.19), sin(angle * 2.0 + t * 0.23));
  v += vec2(0.0, (0.82 + 0.30 * smoothstep(0.0, 0.8, r)) * lift);
  return v;
}

float plume(vec2 uv, vec2 center, float size) {
  vec2 d = uv - center;
  d.x *= RENDERSIZE.x / RENDERSIZE.y;
  return 1.0 - smoothstep(0.0, size, length(d));
}

void main() {
  vec2 uv = isf_FragNormCoord;

  if (PASSINDEX == 0) {
    float frameStep = min(TIMEDELTA * 60.0, 2.0);
    float t = TIME * flowSpeed;
    vec2 vel = velocityField(uv, t) * turbulence;
    vec2 back = uv - vel * (0.00380 * frameStep * flowSpeed);
    vec2 historyBack = uv - vel * (0.00100 * frameStep * flowSpeed);
    vec2 emberBack = uv - vel * (0.00245 * frameStep * flowSpeed);
    vec2 px = 1.0 / RENDERSIZE;

    vec4 center = IMG_NORM_PIXEL(smokeBuffer, back);
    float density = center.r * 0.58;
    density += IMG_NORM_PIXEL(smokeBuffer, back + vec2(2.0 * px.x, 0.0)).r * 0.105;
    density += IMG_NORM_PIXEL(smokeBuffer, back - vec2(2.0 * px.x, 0.0)).r * 0.105;
    density += IMG_NORM_PIXEL(smokeBuffer, back + vec2(0.0, 2.0 * px.y)).r * 0.105;
    density += IMG_NORM_PIXEL(smokeBuffer, back - vec2(0.0, 2.0 * px.y)).r * 0.105;
    density *= pow(dissipation, frameStep);

    float history = IMG_NORM_PIXEL(smokeBuffer, historyBack).g * 0.76;
    history += IMG_NORM_PIXEL(smokeBuffer, historyBack + vec2(px.x, 0.0)).g * 0.06;
    history += IMG_NORM_PIXEL(smokeBuffer, historyBack - vec2(px.x, 0.0)).g * 0.06;
    history += IMG_NORM_PIXEL(smokeBuffer, historyBack + vec2(0.0, px.y)).g * 0.06;
    history += IMG_NORM_PIXEL(smokeBuffer, historyBack - vec2(0.0, px.y)).g * 0.06;
    history *= pow(dissipation, frameStep * 0.20);

    float ember = IMG_NORM_PIXEL(smokeBuffer, emberBack).b * 0.78;
    ember += IMG_NORM_PIXEL(smokeBuffer, emberBack + px).b * 0.055;
    ember += IMG_NORM_PIXEL(smokeBuffer, emberBack - px).b * 0.055;
    ember += IMG_NORM_PIXEL(smokeBuffer, emberBack + vec2(px.x, -px.y)).b * 0.055;
    ember += IMG_NORM_PIXEL(smokeBuffer, emberBack + vec2(-px.x, px.y)).b * 0.055;
    ember *= pow(dissipation, frameStep * 0.48);

    float pulseA = 0.65 + 0.35 * sin(TIME * 2.7);
    float pulseB = 0.55 + 0.45 * sin(TIME * 1.83 + 1.7);
    vec2 emitterA = vec2(0.50 + 0.16 * sin(TIME * 0.57), 0.055);
    vec2 emitterB = vec2(0.30 + 0.12 * sin(TIME * 0.41 + 2.0), 0.045);
    vec2 emitterC = vec2(0.73 + 0.10 * cos(TIME * 0.33), 0.075);
    float source = plume(uv, emitterA, emitterSize) * pulseA;
    source += plume(uv, emitterB, emitterSize * 0.68) * pulseB * 0.72;
    source += plume(uv, emitterC, emitterSize * 0.52) * (1.0 - pulseA) * 0.62;
    source *= 0.78 + 0.22 * sin(uv.x * 47.0 + TIME * 4.0);
    density += source * 0.060 * frameStep;

    float thermal = plume(uv, emitterA + vec2(0.0, 0.020), emitterSize * 0.46);
    thermal += 0.65 * plume(uv, emitterC + vec2(0.0, 0.014), emitterSize * 0.28);
    ember += (thermal * (0.34 + 0.40 * sin(TIME * 5.0 + uv.x * 25.0))
             + density * 0.030) * emberRate * frameStep;
    history = max(history, density * 0.50);
    ember = max(ember, thermal * 0.22);

    float boundary = smoothstep(0.0, 0.03, uv.x)
                   * smoothstep(0.0, 0.03, 1.0 - uv.x)
                   * smoothstep(0.0, 0.025, uv.y)
                   * smoothstep(0.0, 0.06, 1.0 - uv.y);
    density *= boundary;
    history *= boundary;
    ember *= boundary;

    // A soft knee preserves wisps but makes every feedback channel finite.
    float hot = max(density - 0.78, 0.0);
    density = min(density, 0.78) + hot / (1.0 + 0.62 * hot);
    float historyHot = max(history - 0.70, 0.0);
    history = min(history, 0.70) + historyHot / (1.0 + 0.90 * historyHot);
    float emberHot = max(ember - 0.64, 0.0);
    ember = min(ember, 0.64) + emberHot / (1.0 + 1.1 * emberHot);
    gl_FragColor = vec4(clamp(density, 0.0, 1.35),
                        clamp(history, 0.0, 1.20),
                        clamp(ember, 0.0, 1.10), 1.0);
  } else {
    vec3 state = IMG_THIS_PIXEL(smokeBuffer).rgb;
    float density = state.r;
    float history = state.g;
    float ember = state.b;
    vec2 p = isf_FragNormCoord * 2.0 - 1.0;
    p.x *= RENDERSIZE.x / RENDERSIZE.y;

    vec3 cool = smokeColor.rgb;
    vec3 warm = vec3(1.0, 0.22, 0.035);
    vec3 tint = mix(vec3(0.48, 0.22, 0.14), cool, 0.52 + 0.28 * sin(density * 4.0));
    vec3 col = tint * (0.42 * sqrt(max(density, 0.0)) + 2.85 * density * density);
    vec3 afterglow = mix(vec3(0.10, 0.06, 0.28), cool, 0.44);
    col += afterglow * (0.48 * sqrt(max(history, 0.0)) + 0.96 * history * history);
    col += warm * (0.14 * sqrt(max(ember, 0.0)) + 0.98 * ember * ember);

    float veil = 0.5 + 0.5 * sin(9.0 * p.x + 4.0 * p.y + TIME * 0.35);
    col += cool * veil * density * 0.055;
    col *= 1.0 - 0.14 * dot(p, p);
    col *= 1.65;
    col = col / (1.0 + col);
    gl_FragColor = vec4(max(col, 0.0), 1.0);
  }
}