draw method
Implementation
void draw(Canvas canvas, Size size, Paint paint) {
if (lifeTime <= 0) return;
final Rect rect = Rect.fromCenter(
center: pos,
width: particleWidth,
height: particleHeight,
);
paint
..color = particleColor.withAlpha(lifeTime)
..style = fillParticleShape ? PaintingStyle.fill : PaintingStyle.stroke;
canvas.drawPath(particleShape.getOuterPath(rect), paint);
velocity *= 0.9;
lifeTime -= 4;
velocity += acceleration;
pos += velocity;
acceleration = Offset.zero;
}