Write On
The Write On behavior provides a quick way to draw a paint stroke or outline on the
Canvas over time. This allows you to create a handwritten text effect, create the
ever-popular old serial travel map effect, create a hand-sketched alpha mask for a transition
or reveal, create an animated graph for a business presentation, produce graphics to
prevent monitor burn-ins, and so on. The behavior can be applied to a paint stroke created
with the Paint Stroke tool or added to an existing shape. You can have the shape draw,
erase, draw and erase, draw in reverse, and so on, over time.
When Write On is applied to a filled shape with an outline, only the outline of the shape
is drawn.
Note: You can manually animate the First Point Offset and Last Point Offset parameters
in the Style pane of the Shape Inspector to achieve the same effect as the Write On
behavior.
Parameters in the Inspector
Shape Outline:
This pop-up menu determines whether the stroke is drawn, erased, or
drawn and erased.
• Draw: Draws the stroke over the duration of the behavior.
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• Erase: The stroke is completely drawn at the beginning of the behavior and is erased
over the duration of the behavior.
• Draw and Erase: The stroke is drawn, then erased over the duration of the behavior.
• Erase and Draw: The stroke is completely drawn at the beginning of the behavior, is
erased, then is drawn again.
Stroke Length:
This slider defines the length, as a percentage, of the drawn or erased
stroke. A value of 100% uses the entire length of the stroke, bounded by the First Point
Offset and Last Point Offset parameters. If Stroke Length is set to 50%, when 50% of the
stroke is drawn on, it begins to erase (from the beginning of the stroke) so only half of
the length of the stroke is ever displayed over the duration of the behavior.
Stroke Offset:
This slider offsets where the stroke begins on the shape. The value is
expressed as a percentage of the total length of the shape from the start point defined
on the shape.
Direction:
This pop-up menu sets the direction in which the stroke is drawn. There are
two options:
• Forward: The stroke is drawn in a forward direction.
• Reverse: The stroke is drawn in reverse.
Speed:
A pop-up menu that defines the stroke’s “draw-on” velocity from the first to the
last point in the stroke. There are nine options:
• Constant: The stroke is drawn at a steady speed from the first to the last point in the
stroke.
• Ease In: The drawing of the stroke starts at a slow speed, then reaches and maintains
a steady speed through the last point on the stroke.
• Ease Out: The drawing of the stroke starts at a steady speed, then slows down as it
gradually decelerates to a stop at the last point of the stroke.
• Ease Both: The drawing of the stroke slowly accelerates from the first point on the
stroke, and then slows down as it gradually decelerates to a stop at the last point of
the stroke.
• Accelerate: The stroke is drawn with increasing speed.
• Decelerate: The stroke is drawn with decreasing speed.
• Natural: The speed in which the stroke is drawn along the path is determined by the
shape of the path. For example, if the stroke is a U-shape curve, the stroke is drawn
along more quickly as it moves toward the low point of the U, and more slowly as it
moves up the edges.
• Recorded: This option only appears if there is a recorded time over which the stroke
was drawn. In other words, if a shape is converted to a paint stroke, this parameter
does not appear. If the paint stroke is created with the Paint Stroke tool in the toolbar
(using a stylus or mouse), this option does appear.
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• Custom: Custom allows you to draw the stroke along its path by setting keyframes for
the stroke’s speed from 0 to 100%. In other words, you determine what portion of the
stroke is drawn along its path in time.
Custom Speed:
This parameter becomes available when Speed is set to Custom. You
can modify the Custom Speed velocity curve in the Keyframe Editor. For example, you
can keyframe custom values to draw a stroke forward to a specific percentage of its path,
then backward, then forward, and so on before it reaches the end of the animation.
End Offset:
This slider offsets the end of the behavior inward from the defined Out point
and holds the last value. In other words, it offsets the visible paint stroke from the end
of the path of the stroke.
HUD Controls
The Write On HUD contains the Shape Outline, Stroke Length, Stroke Offset, Direction,
Speed, and Custom Speed parameters.