Simulation Behaviors

The Align To Motion behavior changes the rotation of an object to match changes made to its direction along an animation path. This behavior is meant to be combined with Simulation behaviors that animate the position of an object or with a keyframed animation path you create yourself.

Note: The Align to Motion behavior does not work on objects animated using the Motion Path behavior. Instead, use the Snap Alignment to Motion behavior (in the Basic Motion subcategory).

Unlike the Snap Alignment to Motion behavior, which produces absolute changes in rotation that precisely match changes in direction, Align To Motion has a springy reaction and creates a more lively effect.

In the above example, the fish travels along the keyframed animation path, but it isn’t aligned to the animation path (notice the rotation handle). Using the Align To Motion behavior, its angle of rotation moves so it points in the direction of the animation path. By adjusting the Drag parameter, you can make it careen wildly about its anchor point as it goes around curves in the animation path.

This behavior is part of a group of Simulation behaviors that let you create complex animated relationships between two or more objects. These behaviors are extremely powerful and allow complicated effects to be created with a minimum of steps.

An object with the Attracted To behavior moves toward a single specified target, the object of attraction. Additional parameters allow you to adjust the area of influence that defines how close an object must be to move toward the object of attraction, and how strongly it is attracted.

The Drag parameter lets you define whether attracted objects overshoot and bounce about the attracting object, or whether they eventually slow down and stop at the position of the target object.

You can apply two or more Attracted To behaviors to a single object, each with a different object of attraction, to create tug-of-war situations where the object bounces among all objects it’s attracted to.

If you apply an Attractor behavior to an object, other objects that lie within the area of influence move toward it. You can manipulate the strength with which other objects are attracted, as well as the distance required for attraction to begin.

By default, objects overshoot the object of attraction and bounce around, never coming to rest. The Drag parameter lets you adjust this behavior, changing whether attracted objects overshoot and bounce around, or whether they eventually slow down and stop at the position of the target object.

The Attractor behavior can affect all objects in the Canvas that fall within the area of attraction, or you can limit its effect to a specific list of objects by using the Affect parameter.

The Attractor behavior can also be applied to objects in motion. If you animate the position of the target object to which you’ve applied the Attractor behavior, all other objects in the Canvas continue to be attracted to its new position.

This behavior lets you simulate the force of friction on a moving object, slowing it down over time. Applying the Drag behavior is an easy way to decelerate objects with multiple behaviors that create complex motion.

Similar to the Attracted To behavior, but by default an object moves toward the object of attraction and comes to rest, rather than overshooting the object of attraction and bouncing around.

Similar to the Attractor behavior, but by default objects within the area of influence move toward the object of attraction and come to rest, rather than overshooting the object of attraction and bouncing around.

This is a good behavior to use if you’re setting up complex motion simulations and you don’t want your objects exiting the Canvas. Objects with the Edge Collision behavior applied come to a stop or bounce off after colliding with the edge of the Canvas frame. For example, if you apply the Throw behavior to an object and set the velocity to send the object toward the edge of the frame, then apply Edge Collision, the object will bounce off the edge of the frame according to the Bounce Strength parameter.

The angle at which the object bounces depends on the angle at which it hits the edge of the frame; the speed it travels after bouncing is set by the Bounce Strength parameter.

Note: Edge Collision has no effect on objects larger than the Canvas.

Important: By default, the Edge Collision behavior uses the size of the project and the bounding box to determine how the object collides with the edge of the Canvas. For example, in an NTSC Broadcast SD project (720 x 486 pixels), an object bounces off the right and left edges of the project at its bounding box. With groups (particles, text, and objects), only the object’s center is used. You can make the object travel further off the Canvas before it bounces by adjusting the Width and Height parameters. If you’re using this behavior with an object that has an alpha channel that’s smaller than its bounding box, adjust the Crop parameter in the object’s Properties Inspector to fit the bounding box as closely as possible to the edge of the image.

This behavior causes an object, or the objects in a group (when Affect Subobjects is selected), to fall over time. The gravitational acceleration can be increased or decreased, resulting in a change to the rate of fall. Objects affected by the Gravity behavior continue to fall past the bottom edge of the Canvas (unless the Edge Collision behavior has been applied).

The following illustration shows an object affected by the Throw, Snap Alignment to Motion, and Gravity behaviors all at once.

As you can see, the Gravity behavior can be used in conjunction with other behaviors that animate the position of objects to create natural-looking arcs and animation paths that simulate thrown objects falling to the ground. For example, apply the Throw behavior to an object to send it flying through the air, and then apply the Gravity behavior to it to make the object arc up and then fall down past the bottom of the Canvas.

You can also set the Acceleration parameter to a negative value, effectively applying “anti-gravity” to the object and making it fly up.

Similar to the Attracted To behavior, the Orbit Around behavior’s default parameter settings give the object sufficient initial velocity to orbit around another object in a perfect circle.

Note: Behaviors such as Attractor and Repel applied to nearby objects might disrupt an object with the Orbit Around behavior applied to it.

The Random Motion behavior animates the position of an object and makes that object move around the Canvas along a random path.

Although the motion created with this behavior appears to be random, it is predetermined by the group of parameters you’ve chosen. As long as you don’t change the parameters, the animation path created by this behavior remains the same. If you don’t like the path that was randomly generated, click the Generate button in the HUD or the Behaviors Inspector to pick a new random seed number. This number is used to generate a new path.

The Random Motion behavior is useful for creating varied animation paths for large numbers of objects you want to move at the same time. For example, you can create an arrangement of ten objects in the Canvas and apply the Random Motion behavior to them all.

You can also use the Random Motion behavior to add variation to the animation paths created by other behaviors that affect an object’s position. In the following example, adding Random Motion to an object with the Orbit Around behavior results in a more erratic animation path from orbit to orbit, although it still moves around the center as before.

If you apply the Repel behavior to an object, that object pushes away all other objects within the area of influence in the Canvas. The strength with which objects are pushed away can be increased or decreased, as can the distance repelled objects travel.

You can also specify which objects are affected by this behavior, creating an effect where only specific objects are moved, while others remain still.

The Repel behavior is the opposite of the Attractor behavior, and is part of a group of simulation behaviors that create complex animated relationships between two or more objects.

Whereas the Repel behavior pushes other objects away, the Repel From behavior has the converse effect, making the object it’s applied to move away from a selected object in the Canvas.

This behavior is similar to the Drag behavior, except that it affects Rotation instead of position. Rotational Drag simulates friction affecting objects that are spinning due to keyframed or behavior-driven changes to the Rotation parameter. By setting higher Drag values, you can slow rotational changes to an eventual stop.

The Spring behavior creates a relationship between two objects, so an object with the Spring behavior applied to it moves back and forth around a second object. The Attract To parameter defines the object that serves as the target and center of the Spring behavior. Additional parameters let you adjust the speed of the behavior (Spring Tension) and the acceleration of the object at each change in direction (Relaxed Length).

If the Attract To object is at rest, the resulting motion is fairly simple and the springing object moves back and forth in a straight line. If the Attract To object is in motion, the springing object’s motion is much more complex, changing direction according to the velocity of the Attract To object.

The opposite of the Orbit Around behavior. Whereas the Orbit Around behavior causes one object to orbit around another target object, the Vortex behavior exerts a force on all objects surrounding the object to which the Vortex behavior is applied.

Apply the Wind behavior to an object to animate its position and move it in a specified direction. Unlike the Throw behavior, the velocity specified by the Wind behavior is a continuous force, and its parameters can be keyframed to achieve gradual changes in speed and direction.

The Wind behavior is better than the Throw behavior when you want to vary the speed of the affected object. You can apply another behavior (such as Randomize or Ramp) or keyframe the Velocity parameter of the Wind behavior to vary the speed and direction of the object. You cannot make gradual changes in speed or direction with the Throw behavior.