kinoje

Version 0.8 | Entry @ catseye.tc | See also: Canvas Feedback

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kinoje is a templating-based animation tool. A provided template is filled out once for each frame of the animation; the result of the template expansion is used to create a still image; and the resulting sequence of images is compiled into the finished movie.

Quick Start

The following are required:

• Python 3.x — to run the script (2.7 may or may not work)
• PyYAML and Jinja2 — to fill out the templates
• something to create images from filled-out templates — typically POV-Ray or rsvg
• ffmpeg or ImageMagick — to compile the images into a movie file

You might also find VLC useful, for viewing the final movie file.

On Ubuntu 20.04, you can install these with:

pip install --user Jinja2 PyYAML  # you may want to make a virtualenv first
sudo apt install povray povray-includes librsvg2 ffmpeg imagemagick vlc

(Or, if you would like to use Docker, you can pull a Docker image from catseye/kinoje on Docker Hub, following the instructions given on that page.)

Once installed, you can run the tool from the repository directory like so:

bin/kinoje eg/moebius.yaml

Since no output filename was given, kinoje assumes MPEG Layer 4 format and automatically picks a reasonable filename, in this case moebius.mp4.

Other Invokation Options

You can also ask it to create a GIF by specifying an output filename with that as its file extension:

bin/kinoje eg/squares.yaml -o squares.gif

Multiple configuration files can be specified on the command line; successive configurations will act as overlays, overriding the settings in them. In fact individual settings can be given in the format +name=value. For example,

bin/kinoje eg/moebius.yaml overlays/tiny.yaml +duration=4.0

The --work-dir option can be given to make kinoje store its working files in a specified directory. The directory will be created if it does not yet exist. If the directory contains incomplete working files from a previous run of kinoje, the process will continue where it left off.

Theory of Operation

The kinoje executable actually calls 3 other executables:

• kinoje-expand fills out the template multiple times, once for each frame of the movie, and saves the expanded templates (which we call "instants") into a directory.
• kinoje-render takes a directory of instants and creates a set of images, one for each instant, in another directory. It calls a rendering command specified in the config to do this.
• kinoje-compile takes a directory of images and turns them into a movie file (.mp4 or .gif).

These executables can also be called directly, if you e.g. already have a directory of instants you want to render and compile into a final movie.

File Format

The input config file must contain, at the minimum, a key called template containing the template, and a key duration which specifies the duration in seconds of the movie. It may also contain the following keys, or if not, the following defaults will be used:

• start: 0.0
• stop: 1.0
• fps: 25.0
• width: 320
• height: 200

The template is typically a multi-line string in Jinja2 syntax, which will be filled out once for each frame. The context with which it will be filled out is constructed as follows:

• t is a floating point value which will vary from 0.0 on the first frame to 1.0 on the last frame. It is this value which will typically drive the animation. For example, if the animation consists of moving a circle from x=0 to x=10, the part of the template which gives the x co-ordinate of the circle would be written as {{ t * 10.0 }}.

  And actually this is not 100% true. t would be 1.0 on the frame after the last frame which, by definition, is never rendered. On the last frame, it is 1.0 less a small value, which we could call the t-delta, and which varies based on the duration and the frame rate.

• math, which is Python's math module, and which can be used to access functions such as sin.

• tween, which is a function which is currently undocumented.

• fmod, which is a function which is currently undocumented.

Other configuration options:

• duration gives the duration, in seconds, to make the movie. If omitted, it needs to be supplied on the command-line with the --duration option.

No further documentation on how to use the tool will be given, as it is all very subject to change right now.