Track shapes, masks, and paint strokes

The Track Points behavior (located in the Shape Behaviors category) is designed for use with shapes, masks, and paint strokes.

Use the Track points behavior in the following ways:

  • To track the control points of a shape or mask to a clip (for example, when rotoscoping)

  • To apply tracking data from another tracking analysis to the control points of a shape or mask

  • To apply the animation of an object to the control points of a shape or mask

The Track Points behavior does not work with simple shapes (made with the Rectangle, Circle, and Line tools) because they contain no control points. If you apply a Track Points behavior to a simple shape, a dialog appears asking if you want to convert the shape to apply the Shape behavior.

Note: To apply the analyzed movement of an object to a shape or mask as a whole (not to the shape’s control points), use the Match Move behavior.

For a full description of the Track Points parameters, see Track Points controls.

Track a mask using the Track Points behavior

In the following example, the Track Points behavior is applied to a loose mask of seven control points, isolating a car in a background clip.

  1. With a background clip visible in the Canvas, use a mask tool to isolate part of the background clip.

    For more information on working with masks, see Masks and transparency overview.

  2. Select the mask object, then click the Add Behavior pop-up menu in the toolbar and choose Shape > Track Points.

    The behavior is added to the mask object, and trackers appear for each control point on the shape. The trackers are arrayed in the same order that the shape was drawn: Control Point 1 is Track 1, Control Point 2 is Track 2, and so on.

    Canvas showing several trackers applied to object
  3. Drag the trackers to fine-tune their position on the reference patterns of the background footage.

    As you drag, a magnified inset view of the area around the tracker appears.

    Canvas showing magnified inset that appears when tracker is dragged
  4. To disable a tracker, deselect its checkbox in the Behaviors Inspector.

    Note: Control points without an associated tracker are not modified.

  5. Click the Analyze button in the HUD or Behaviors Inspector.

    The mask control points are tracked to the reference patterns in the background footage.

    In this example, a mask is tracked to a moving car so the car can be isolated from the rest of the clip. The illustration on the left shows the original unmodified clip. In the illustration on the right, the tracked mask isolates the car, allowing separate effects to be applied to the car and its background even though they’re part of the same image. The mask protects the car from the effects of the heavy blur and desaturation.

    Canvas showing a tracked mask

    As with all behaviors, you can drag or copy (by Option-dragging) a Track Points behavior to a new shape in the Layers list. When you apply the behavior to a new shape, the trackers are applied to the control points of the new shape. If the new shape has more control points than the originally tracked shape, only the original track points are applied. For example, if the originally tracked shape has three control points, and the new shape has five control points, trackers are applied to the first three control points of the new shape. If the new shape has fewer control points than the originally tracked shape, trackers are applied to the existing points on the new shape.

    Note: Paint strokes usually have a large number of control points. Simplify a paint stroke by deleting or disabling control points before applying a Track Points behavior to the stroke. To track the stroke as a whole, rather than by its control points, use the Match Move behavior. For more information about paint strokes, see Paint strokes overview.

Apply the animation of one shape to the control points of another shape

Applying the animation of one animated shape to another is an easy way to create fun, complementary animations in which the objects appear to play with each other. For this workflow, your project must contain an object animated with keyframes or behaviors.

  1. In a project that contains two shapes, animate one of the shapes using keyframes or a Basic Motion behavior.

    In this example, a simple line shape is animated with the Spin behavior.

    For more information about animating with keyframes, see Keyframing overview. For more information about Basic Motion behaviors, such as the Spin behavior see Spin.

  2. Apply the Track Points behavior to a nonanimated shape.

    The Track Points behavior inherits the animation data of the animated object closest to it in the Layers list. (A thumbnail of the animated object appears in the Source well of the Track Points Behaviors Inspector.)

    In this example, the Track Points behavior is applied to a Bezier shape.

    Canvas showing source object, Bezier shape with Track Points behavior, and HUD showing referenced source object

    Note: To reference different animated object, drag that object to the Track Points behavior’s Source well in the Behaviors Inspector or to the behavior object in the Layers list.

  3. In the Behaviors Inspector, click the Transform pop-up menu, then choose Attach to Source.

    The spinning animation of the line is applied to the Bezier shape. The Bezier shape changes form because the vertex tangents match the transformation of the source animation.

    Canvas showing two objects moving in tandem while retaining their original relative positions
  4. To align the tangents to the transformation of the source object, select the Align Tangents checkbox in the Behaviors Inspector.

     Align Tangents checkbox

    The spinning animation of the line is applied to the Bezier shape. The tangents remain aligned at their original angles along the shape.

    Canvas showing same two objects with Align Tangents checkbox selected

    Note: By default, the Transform pop-up menu is set to Mimic Source. For more information on the Transform pop-up menu, see Track Points controls.