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Please note that This document is no longer up-to-date.
This document is still valid in terms of the idea it coveys. However, meanwhile there
has been published a paper that covers the same topic in a more general and comprehensive
way.
To the paper: Linear Filters - Animating Objects in a Flexible and Pleasing Way
If you decide to continue reading this document, please keep in mind that now some fields have
changed their name, and that besides Damper nodes there is also the class
of Chaser nodes.
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Case 1: A Simple Door.
Making a door that opens or closes when the user clicks on it, depending
of whether it is already open, is a simple task in VRML. (As it should be.)
One uses a TouchSensor, an
OrientationInterpolator for the opening animation,
another
OrientationInterpolator for the closing animation
and a Script node for deciding which of the
two animations should be started.
However there is a problem:
What happens if the user
clicks on the door while the door is moving from one state to the other?
With standard nodes in VRML it is not easy to make this animation realistic.
Depending on how, and whether the author tries to circumvent this lack of realism
the door jumps from one position to another, or simply does not react to the
users mouse click.
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See this example:
Door-Classical.wrl
It shows an animated door
based on the node structure
shown on the right.
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The Damper nodes avoid this with an even simpler structure:
Using the Damper nodes one
can easily create such an animation without worrying what happens if the user
clicks on the touch sensor in the wrong moment. The schema to do this is even simpler:
When triggered by the TouchSensor the Script
node sends either the SFRotation value for an opened or for a closed
door to the Damper node. (that's all).
The Damper then creates the animation from the current position
to the position requested by the Script node. It takes into account
the current direction and speed of movement, if any.
Case 2: Responding to User Input.
The Damper nodes allow
to create animations by just giving the destination position. One does not need the
skills to dynamically fill the keyValue
array of an Interpolator node and to manage
startTime and stopTime correctly.
Imagine an application where the user can place furniture inside a room by clicking
on the walls, floor, etc.
It can be done by associating a TouchSensor with
each of the walls, floor and ceiling and with a Script
node that generates the appropriate positions and orientations when a
TouchSensor has been clicked.
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The example
Room-Direct.wrl
demonstrates this.
It's based on the
node structure shown on the right.
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In the above example the picture directly jumps to the new location.
By inserting a Damper node between
the Script and the Transform
the movement becomes animated.
That's all about creating animations with Dampers.
To tweak the parameters for speed and smoothness, look at the
Damper documentation.
Here is an alternative version that responds more quickly:
Room-Dampered-Fast.wrl
Providing initial values
In the above examples the picture always starts being stuck in the ground.
This comes because the Damper nodes begin with
zeroes as their output values by default. To set another initial value,
use the initial_output and initial_input
fileds. One must set both fields to the same value, because otherwise this would
create an animation from initial_output to initial_input.
Case 3: Smoothing existing animations.
While the above two cases used the Dampers for
creating animations, this case uses them for refining existing
animations. Thus, while only few animation keys need to be specified in the
Interpolators,
the resulting animation consist of smooth curves.
Please note that in these two examples there are some Viewpoints defined for watching the coaster from
different angles.
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end of document
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