skia2/resources/particles/fireworks.json

{
   "MaxCount": 300,
   "Drawable": {
      "Type": "SkCircleDrawable",
      "Radius": 3
   },
   "Code": [
      "void effectSpawn(inout Effect effect) {",
      "  // Phase one: Launch",
      "  effect.lifetime = 4;",
      "  effect.rate = 120;",
      "  float a = radians(mix(-20, 20, rand(effect.seed)) - 90);",
      "  float s = mix(200, 220, rand(effect.seed));",
      "  effect.vel.x = cos(a) * s;",
      "  effect.vel.y = sin(a) * s;",
      "  effect.color.rgb = float3(rand(effect.seed), rand(effect.seed), rand(effect.seed));",
      "  effect.pos.x = 0;",
      "  effect.pos.y = 0;",
      "  effect.scale = 0.25;  // Also used as particle behavior flag",
      "}",
      "",
      "void effectUpdate(inout Effect effect) {",
      "  if (effect.age > 0.5 && effect.rate > 0) {",
      "    // Phase two: Explode",
      "    effect.rate = 0;",
      "    effect.burst = 50;",
      "    effect.scale = 1;",
      "  } else {",
      "    effect.vel.y += dt * 90;",
      "  }",
      "}",
      "",
      "void spawn(inout Particle p) {",
      "  bool explode = p.scale == 1;",
      "",
      "  p.lifetime = explode ? (2 + rand(p.seed) * 0.5) : 0.5;",
      "  float a = radians(rand(p.seed) * 360);",
      "  float s = explode ? mix(90, 100, rand(p.seed)) : mix(5, 10, rand(p.seed));",
      "  p.vel.x = cos(a) * s;",
      "  p.vel.y = sin(a) * s;",
      "}",
      "",
      "void update(inout Particle p) {",
      "  p.color.a = 1 - p.age;",
      "  if (p.scale == 1) {",
      "    p.vel.y += dt * 50;",
      "  }",
      "}",
      ""
   ],
   "Bindings": []
}