Simple particles system in Graphx.

particles.dart

/// Author: roipeker 2023.
/// 
/// Particles in GraphX
///
/// video example:
/// https://giphy.com/gifs/VXZ0GvQSRh49AUYX9b
///


Future<void> addParticles() async {
  /// creating a circle texture for quick demo... u can use any png.
  var texture =
      await GTextureUtils.createCircle(color: Colors.red, radius: 10);

  var particles = GSimpleParticleSystem();
  addChild(particles);

  /// position emitter on screen.
  particles.x = 100;
  particles.y = 100;

  /// how many particles to emit per second.
  particles.emission = 40;
  // how much variance in the emission rate.
  // this might be between 40 and 50 particles (+10).
  particles.emissionVariance = 10;
  // for how long the particles will be emitted per cycle.
  // 3 seconds.
  particles.emissionTime = 3.0;
  // 1 second delay before emitting particles cycle.
  particles.emissionDelay = 1.0;
  particles.blendMode = BlendMode.screen;
  particles.particleBlendMode = BlendMode.modulate;
  particles.texture = texture;
  // particles will render WHITE by default...
  // so you can tint them accordingly in transition.
  particles.endColor = Colors.yellow.value;
  particles.initialColor = Colors.blue.value;

  // end scale is the scale the particle will have when it's dead.
  particles.endScale = .1;
  // "randomness" between .1 and .4.
  particles.endScaleVariance = .3;

  particles.endAlpha = 0;

  /// This will take particle coordinates globally.
  /// So the parent transform does not change the particles
  /// after emission.
  particles.useWorldSpace = true;
  particles.initialAlpha = .7;
  particles.initialAlphaVariance = .4;
  particles.initialScale = .3;
  particles.initialScaleVariance = .8;

  particles.dispersionAngle = Math.PI / 2;
  particles.dispersionAngleVariance = Math.PI / 4;
  particles.initialVelocity = 2;
  particles.initialVelocityVariance = 1;
  particles.initialAcceleration = .5;

  // for how "long" the particle will live.
  // 1 seconds.
  particles.energy = 1;
  // extra time variation for the particle life.
  particles.energyVariance = .5;

  // changes the pivot point of each particle texture.
  // this is useful to create a cool effect when the particles
  // are rotating.
  particles.particlePivotX = 20;
  particles.particlePivotY = 20;

  particles.initialAngularVelocityVariance = .005;

  // coordinates where the particles are created.
  particles.dispersionXVariance = 10;
  particles.dispersionYVariance = 10;

  /// create a BURST of particles.
  stage!.onMouseDown.add((e) {
    particles.burst = true;

    /// stop bursting, and start emitting.
    stage!.onMouseUp.addOnce((e) {
      particles.burst = false;
      particles.emit = true;
    });
  });

  /// Move particles with mouse
  /// (shows the useWorldSpace property).
  /// try to rotate the emitter as well :)
  stage!.onMouseMove.add((e) {
    particles.x = mouseX;
    particles.y = mouseY;
  });
}