A Visual Introduction to the Flint Particle System

Description: The ‘Move’ action updates the position of particles based on its velocity. This is essential for almost every particle system. If you want animated particles, you need the ‘Move’ class.

Implementation: This file outputs particles with an initial velocity of (-35, 0). Since there is no acceleration or friction, the particles keep moving at a steady speed forever. Simple, but necessary.

Description: The ‘Accelerate’ action adjusts the velocity of each particle by a constant acceleration. A common application of ‘Acceleration’ is the simulation of gravity.

Implementation: This file outputs particles with an initial velocity of (-30, -50). An acceleration of (0, -25) is applied to each particle, causing it to drop in a parabolic arch.

Description: The ‘Friction’ action applies friction to particles, causing them to slow down when they are moving.

Implementation: This file outputs particles from two separate points with an initial velocity of (-65, 0). When a particle reaches the gray area, friction is applied to it. The bottom particles are a control stream with no friction applied to it. This makes the friction’s deceleration effect more apparent.

Description: The ‘RandomDrift’ action moves particles by a random small amount every frame, causing them to drift around. This is great for smoke, fire, and snowfall.

Implementation: This file outputs particles with an initial velocity of (0, -50). Instead of flying straight up, they drift around as they rise.

Description: The ‘BoundingBox’ action confines each particle to a rectangular region. Notice that the particles bounce off of the walls, but not off of each other. This is because the ‘Bounding Box’ action only controls collisions with regions, whereas The ‘Collide’ action controls collisions with other particles.

Implementation: This file starts with 60 particles in random positions with random velocities. When a particle hits the edge of the bounding box, it bounces off in another direction. Be sure to use the ‘CollisionRadiusInit‘ Initializer when using this class.

Description: The ‘Collide’ action detects collisions between particles and modifies their velocities in response to the collision.

Implementation: This file starts with 60 particles in random positions with random velocities, as well as a ‘Bounding Box’ (seen in gray outline). Particles will bounce off of the bounding box, as well as each other. Be sure to use the ‘CollisionRadiusInit’ and ‘MassInit’ Initializers when using this class.

Description: The ‘MutualGravity’ action applies forces to attract each particle towards the other particles.

Implementation: This file creates 16 particles randomly distributed on stage. The ‘MutualGravity’ action causes each particle to approach the other particles. A ‘MinimumDistance’ action is also applied to prevent the particles from sticking together.

Description: The ‘ApproachNeighbours’ action applies a static acceleration to each particle to draw it towards other nearby particles. This is different from ‘MutualGravity’, since the strength of the acceleration is independent of distance.

Implementation: This file creates 15 particles randomly distributed on stage. The ‘ApproachNeighbours’ action causes each particle to approach the other particles. This causes them to cluster, but it doesn’t cause them to point in the same direction. You need to add a ‘Match Velocity’ action to achieve that effect. A ‘MinimumDistance’ action is also applied to prevent the particles from sticking together.

Description: The ‘MatchVelocity’ action applies an acceleration to each particle to match its velocity to that of its nearest neighbours.

Implementation: This file generates 2 particles that will intersect. When they are close enough, ‘MatchVelocity’ forces them to point in the same direction, instead of colliding.

Description: The ‘MinimumDistance’ action applies an acceleration to the particle to maintain a minimum distance between it and its neighbours. This is useful when you want to prevent particles from clustering.

Implementation: This file creates 15 particles, distributed randomly. Whenever a particle comes within 75 pixels of another particle, an acceleration is applied to push it in the opposite direction of that particle.

Description: Flocking is not a built-in action, but the effect can be achieved by combining ‘ApproachNeigbours’, ‘MatchVelocity’, and ‘MinimumDistance’.

Implementation: This file creates 35 particles, distributed randomly. ‘ApproachNeighbours’, ‘MatchVelocity’, and ‘MinimumDistance’ actions are applied to simulate the flocking behavior. A minimum speed limit of 100 is also applied to keep the flock moving around.

Description: The ‘Age’ action operates in conjunction with the ‘Lifetime’ Initializer. It causes the energy property of each particle to decline according to a specified easing function. When the particle energy level reaches 0, it ‘dies’ (it is removed from the particle system).

Implementation: This file creates 30 particles with a ‘Lifetime’ ranging from 2 to 50. The ‘Age’ action uses a quadratic ease out function to change the energy level of the particles. A ‘Fade’ action was added so you can actually see the particles disappear as they age.

Description: The Fade action uses particles’ energy levels to determine their alpha. The Flint documentation says that you should use this in conjunction with the ‘Age’ action, but that’s not the only way to use ‘Fade’. If you create your own method of changing the particles’ energy level, you can use ‘Fade’ without aging the particles.

Implementation: This file demonstrates a method of using ‘Fade’ without the ‘Age’ action. Whenever particles collide, their energy level is reduced. The ‘Fade’ action reflects this reduction by lowering the particle’s alpha.

Description: The ‘ColorChange’ action alters the color of the particles according to their energy level. The Flint documentation says that you should use this in conjunction with the ‘Age’ action, but that’s not the only way to use ‘ColorChange’. If you create your own method of changing the particles’ energy level, you can use ‘ColorChange’ without aging the particles.

Implementation: This file demonstrates a method of using ‘ColorChange’ without the ‘Age’ action. Whenever particles collide, their energy level is reduced. The ‘ColorChange’ action reflects this change by interpolating their color from yellow to red.

Description: The ‘ScaleAll’ action adjusts the size of each particle’s image, collision radius and mass according to its energy level. The Flint documentation says that you should use this in conjunction with the ‘Age’ action, but that’s not the only way to use ‘ScaleAll’. If you create your own method of changing the particles’ energy level, you can use ‘ScaleAll’ without aging the particles.

Implementation: This file demonstrates a method of using ‘ScaleAll’ without the ‘Age’ action. Whenever particles collide, their energy level is reduced. The ‘ScaleAll’ action reflects this change by changing their size, collision radius and mass.

Description: The ‘GravityWell’ action applies a force on the particles to draw them towards a single point. This is very useful for simulating physics.

Implementation: This file generates bursts of particles that orbit a ‘GravityWell’ located at the center of the stage.

Description: The ‘AntiGravity’ action applies a force on the particles to push them away from a single point.

Implementation: This file generates bursts of particles that orbit an ‘AntiGravity’ action located at the center of the stage.

Description: The ‘Jet’ action applies an acceleration to particles only if they are in the specified zone.

Implementation: This file generates bursts of particles that speed up as they cross a ‘Jet’ zone.

Description: The ‘Explosion’ action applies a force on the particles to push them away from a single point.

Implementation: This file creates an explosion at the center of the screen, forcing all of the particles off screen.

Description: The ‘DeathZone’ action marks particles as dead if they are inside a specific zone. You can also invert the effect and create a ’safe zone’ by marking all particles as dead if they are outside a specific zone.

Implementation: This file generate bursts of particles that disappear when they hit the ‘DeathZone’ at the center of the stage.

Description: The ‘TweenToZone’ action adjusts each particle’s position between two locations according to its energy level. This is typically use in conjunction with the ‘Age’ action.

Implementation: This file creates a particle tween between two zones by drawing dynamic text fields onto a BitmapData object, then using this BitmapData to define Flint’s BitmapDataZone.

Description: The ‘ZonedAction’ action applies an action to the particles only if they are in the specified zone. This can be used in conjunction with any other action.

Implementation: This file generates tightly-clustered bursts of particles that undergo a ‘RandomDrift’ effect at the center of the stage, causing them to scatter.

Description: The ‘MouseGravity’ action applies a force on each particle to draw it towards the mouse.

Implementation: This file creates 35 particles that gravitate towards the mouse pointer. A ‘MinimumDistance’ action is also applied to keep the particles from clustering.

Description: The ‘TurnTowardsMouse’ action causes each particle to constantly adjust its direction so that it travels towards the mouse pointer. This action doesn’t apply any acceleration to the particles, it only changes the direction of the particles’ existing velocity.

Implementation: This file creates 35 particles that always point towards the mouse. A ‘MinimumDistance’ action is also applied to keep the particles from clustering.

Description: The ‘KeyDownAction’ action applies another action only when the user presses a key. The key to press can be specified, which means that you can associate different actions with different keystrokes.

Implementation: This file creates 35 particles that you can control with the arrow keys. First, click on the stage to give the Flash Player focus. Then, use the arrow keys to apply acceleration to the particles.