Optimizations to particle systems. Uses single instance of Random and faster atan2 function.

packages/flutter/example/game/lib/particle_system.dart

@@ -80,8 +80,6 @@ class ParticleSystem extends Node {
   // double _elapsedTime;
   int _numEmittedParticles = 0;
 
-  math.Random _rand;
-
   ParticleSystem(this.texture,
                  {this.life: 1.5,
                   this.lifeVar: 1.0,
@@ -116,7 +114,6 @@ class ParticleSystem extends Node {
                   this.numParticlesToEmit: 0,
                   this.autoRemoveOnFinish: true}) {
     _particles = new List<_Particle>();
-    _rand = new math.Random();
     _emitCounter = 0.0;
     // _elapsedTime = 0.0;
     if (gravity == null) gravity = new Vector2.zero();
@@ -124,6 +121,8 @@ class ParticleSystem extends Node {
   }
 
   void update(double dt) {
+    // TODO: Fix this (it's a temp fix for low framerates)
+    if (dt > 0.1) dt = 0.1;
 
     // Create new particles
     double rate = 1.0 / emissionRate;
@@ -196,34 +195,34 @@ class ParticleSystem extends Node {
     _Particle particle = new _Particle();
 
     // Time to live
-    particle.timeToLive = math.max(life + lifeVar * randMinus1To1(), 0.0);
+    particle.timeToLive = math.max(life + lifeVar * randomSignedDouble(), 0.0);
 
     // Position
     Point srcPos = Point.origin;
-    particle.pos = new Vector2(srcPos.x + posVar.x * randMinus1To1(),
-                               srcPos.y + posVar.y * randMinus1To1());
+    particle.pos = new Vector2(srcPos.x + posVar.x * randomSignedDouble(),
+                               srcPos.y + posVar.y * randomSignedDouble());
 
     // Size
-    particle.size = math.max(startSize + startSizeVar * randMinus1To1(), 0.0);
-    double endSizeFinal = math.max(endSize + endSizeVar * randMinus1To1(), 0.0);
+    particle.size = math.max(startSize + startSizeVar * randomSignedDouble(), 0.0);
+    double endSizeFinal = math.max(endSize + endSizeVar * randomSignedDouble(), 0.0);
     particle.deltaSize = (endSizeFinal - particle.size) / particle.timeToLive;
 
     // Rotation
-    particle.rotation = startRotation + startRotationVar * randMinus1To1();
-    double endRotationFinal = endRotation + endRotationVar * randMinus1To1();
+    particle.rotation = startRotation + startRotationVar * randomSignedDouble();
+    double endRotationFinal = endRotation + endRotationVar * randomSignedDouble();
     particle.deltaRotation = (endRotationFinal - particle.rotation) / particle.timeToLive;
 
     // Direction
-    double dirRadians = convertDegrees2Radians(direction + directionVar * randMinus1To1());
+    double dirRadians = convertDegrees2Radians(direction + directionVar * randomSignedDouble());
     Vector2 dirVector = new Vector2(math.cos(dirRadians), math.sin(dirRadians));
-    double speedFinal = speed + speedVar * randMinus1To1();
+    double speedFinal = speed + speedVar * randomSignedDouble();
     particle.dir = dirVector.scale(speedFinal);
 
     // Radial acceleration
-    particle.radialAccel = radialAcceleration + radialAccelerationVar * randMinus1To1();
+    particle.radialAccel = radialAcceleration + radialAccelerationVar * randomSignedDouble();
 
     // Tangential acceleration
-    particle.tangentialAccel = tangentialAcceleration + tangentialAccelerationVar * randMinus1To1();
+    particle.tangentialAccel = tangentialAcceleration + tangentialAccelerationVar * randomSignedDouble();
 
     // Color
     particle.colorPos = 0.0;
@@ -248,7 +247,7 @@ class ParticleSystem extends Node {
       double scos;
       double ssin;
       if (rotateToMovement) {
-        double extraRotation = math.atan2(particle.dir[1], particle.dir[0]);
+        double extraRotation = GameMath.atan2(particle.dir[1], particle.dir[0]);
         scos = math.cos(convertDegrees2Radians(particle.rotation) + extraRotation) * particle.size;
         ssin = math.sin(convertDegrees2Radians(particle.rotation) + extraRotation) * particle.size;
       } else {
@@ -276,14 +275,12 @@ class ParticleSystem extends Node {
     Paint paint = new Paint()..setTransferMode(transferMode)
         ..setFilterQuality(FilterQuality.low) // All Skia examples do this.
         ..isAntiAlias = false; // Antialiasing breaks SkCanvas.drawAtlas?
-    // return canvas.drawAtlas(texture.image, transforms, rects, colors,
-    //   TransferMode.modulate, null, paint);
+    return canvas.drawAtlas(texture.image, transforms, rects, colors,
+      TransferMode.modulate, null, paint);
 
     dartDrawAtlas(canvas, texture.image, transforms, rects, colors,
       TransferMode.modulate, paint);
   }
-
-  double randMinus1To1() => _rand.nextDouble() * 2.0 - 1.0;
 }
 
 void dartDrawAtlas(Canvas canvas, Image image, List<RSTransform> transforms,

packages/flutter/example/game/lib/util.dart

 part of sprites;
 
+
+math.Random _random = new math.Random();
+
+// Random methods
+
+double randomDouble() {
+  return _random.nextDouble();
+}
+
+double randomSignedDouble() {
+  return _random.nextDouble() * 2.0 - 1.0;
+}
+
+int randomInt(int max) {
+  return _random.nextInt(max);
+}
+
+// atan2
+
+class GameMath {
+  static bool _inited = false;
+
+  static final int size = 1024;
+  static final double stretch = math.PI;
+
+  static final int ezis = -size;
+
+  static Float64List atan2_table_ppy = new Float64List(size + 1);
+  static Float64List atan2_table_ppx = new Float64List(size + 1);
+  static Float64List atan2_table_pny = new Float64List(size + 1);
+  static Float64List atan2_table_pnx = new Float64List(size + 1);
+  static Float64List atan2_table_npy = new Float64List(size + 1);
+  static Float64List atan2_table_npx = new Float64List(size + 1);
+  static Float64List atan2_table_nny = new Float64List(size + 1);
+  static Float64List atan2_table_nnx = new Float64List(size + 1);
+
+  static void init() {
+    if (_inited) return;
+
+    for (int i = 0; i <= size; i++) {
+      double f = i.toDouble() / size.toDouble();
+      atan2_table_ppy[i] = math.atan(f) * stretch / math.PI;
+      atan2_table_ppx[i] = stretch * 0.5 - atan2_table_ppy[i];
+      atan2_table_pny[i] = -atan2_table_ppy[i];
+      atan2_table_pnx[i] = atan2_table_ppy[i] - stretch * 0.5;
+      atan2_table_npy[i] = stretch - atan2_table_ppy[i];
+      atan2_table_npx[i] = atan2_table_ppy[i] + stretch * 0.5;
+      atan2_table_nny[i] = atan2_table_ppy[i] - stretch;
+      atan2_table_nnx[i] = -stretch * 0.5 - atan2_table_ppy[i];
+    }
+    _inited = true;
+  }
+
+  static double atan2(double y, double x) {
+    if (!_inited)
+      init();
+
+    if (x >= 0) {
+      if (y >= 0) {
+        if (x >= y)
+          return atan2_table_ppy[(size * y / x + 0.5).toInt()];
+        else
+          return atan2_table_ppx[(size * x / y + 0.5).toInt()];
+      } else {
+        if (x >= -y)
+          return atan2_table_pny[(ezis * y / x + 0.5).toInt()];
+        else
+          return atan2_table_pnx[(ezis * x / y + 0.5).toInt()];
+      }
+    } else {
+      if (y >= 0) {
+        if (-x >= y)
+          return atan2_table_npy[(ezis * y / x + 0.5).toInt()];
+        else
+          return atan2_table_npx[(ezis * x / y + 0.5).toInt()];
+      } else {
+        if (x <= y)
+          return atan2_table_nny[(size * y / x + 0.5).toInt()];
+        else
+          return atan2_table_nnx[(size * x / y + 0.5).toInt()];
+      }
+    }
+  }
+}