= Animating Data with ParaView Python Scripting =
Some information on how to write Python scripts to animate your data with ParaView can be found here:\\
https://www.paraview.org/Wiki/ParaView/Python_Scripting\\
https://www.paraview.org/ParaView3/Doc/Nightly/www/py-doc/paraview.servermanager_proxies.html

On this page, we would like to share our own experience with you. DISCLAIMER: our knowlegde about all this is not complete and maybe incorrect. So believe everything found on this page on your own risk.

== ParaView Gui: Animation View ==
As usual, when you want to write a Python script for ParaView from scratch, and have no idea where to start, it make sense to open the ParaView GUI, start a Python trace, and prototype the desired setup in the GUI interactively. When you want to generate an animation, you have to deal with the Animation View, obviously.

[[Image(ParaView_AnimationView.jpg, margin=10)]]\\

Unfortunately, ParaView is not willing to include all interactive settings in the trace. Some are just skipped, e.g. settings regarding the "TimeKeeper1 - Time" are NOT reflected in the trace. For this reason it makes sense to take a more closer look at the mechanisms and Python classes working behind the scene.

== Basic Concept ==
The basic concept of how to animate "something", in this case the rendered ParaView scene, is quite easy to understand. The central element of any animation is a timeline with a start and end time and, as we work with discrete timesteps, a number of frames. This is implemented in the Python class paraview.simple.AnimationScene.
Within the time interval defined in the timeline, properties of the scene can be changed.
In the ParaView GUI this concept is reflected by so called "tracks" (or "cues") in the Animation View. Basically, each track defines the temporal change of one (or more) properties of the scene.

In ParaView-Python, different kinds (classes) of tracks/cues are available. Here we will try to explain four of them, which are implemented in the following Python classes:
* paraview.simple.KeyFrameAnimationCue: basic cue to animate general properties of objects (readers, sources, filters) in the render pipeline
* paraview.simple.CameraAnimationCue: cue to change camera parameters (e.g. position, focal point, up direction, view angle)
* paraview.simple.PythonAnimationCue: cue to execute a Python script at a certain point in time
* paraview.simple.TimeAnimationCue: cue to determine what data timesteps are loaded depending on the animation clock time

The (change of the) values of the properties in the timeline are defined by one or more keyframes included in each track. The key elements :) of a keyframe are keytime and keyvalues. The value(s) of the referred property is set to the keyvalues at the specified keytime. Some types of keyframes also have the ability to interpolate keyvalues from one keyframe to the next. Specifically these are paraview.simple.CameraKeyFrame, paraview.simple.CompositeKeyFrame, paraview.simple.ExponentialKeyFrame, paraview.simple.RampKeyFrame and paraview.simple.SinusoidKeyFrame.

In the next paragraphs we are going to explain the basic mechanisms of the relevat Python classes and we give some examples of typical use cases.

== Class !AnimationScene ==
The !AnimationScene is responsible for steering the animation clock time.
For this purpose, the !AnimationScene has a !StartTime, an !EndTime, and a mechanism to determine the discrete time steps it will generate between !StartTime and !EndTime. The descrete timesteps are determined by the Mode (called !PlayMode in Python) of the !AnimationScene. Three different Modes are avilable:
* 'Sequence': the timesteps are defined by the property !NumberOfFrames
* 'Snap To !TimeSteps': the descrete timesteps are defined by the timesteps available in the (time dependend) data. The !AnimationScene has knowledge about the available data timesteps by the help of a seperate object, the !TimeKeeper.
* '!RealTime': the timesteps are calculated on the fly (while rendering) to achieve a certain duration of the rendering. This mode is not useful for typical Python scripting, though.

Important properties of !AnimationScene:
* !StartTime: the start time of the animation
* !EndTime: the end time of the animation
* !PlayMode: either 'Sequence', 'Snap To !TimeSteps' or '!RealTime'
* !NumberOfFrames: number of frames, only used when !PlayMode is set to 'Sequence'
* !AnimationTime: the actual animation clock time. Can be get or set.
* !TimeKeeper: the !TimeKeeper-object

Important methods of !AnimationScene:
* !GoToFirst(): goto first frame
* !GoToLast(): goto last frame
* !GoToNext(): goto next frame
* !GoToPrevious(): goto previous frame

=== Use Case ===
Get the animation scene and play a sequence of 100 timesteps:
{{{
#!python
animationScene = GetAnimationScene()
animationScene.StartTime = 0
animationScene.EndTime = 1
animationScene.NumberOfFrames = 100
animationScene.PlayMode = 'Sequence'
animationScene.GoToFirst()
while True:
   # render scene
   # safe image
   if animationScene.AnimationTime == animationScene.EndTime:
      break
   anmationScene.GoToNext()
}}}

Get the animation scene and play all available timesteps of the time dependent data:
{{{
#!python
animationScene = GetAnimationScene()
animationScene.PlayMode = 'Snap To TimeSteps'
animationScene.GoToFirst()
while True:
   # render scene
   # safe image
   if animationScene.AnimationTime == animationScene.EndTime:
      break
   anmationScene.GoToNext()
}}}