Write Inkscape extensions that modify objects

Tutorial – Tremble

Article from Issue 240/2020
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Writing your own extension for Inkscape opens up a whole world of possibilities. Apart from creating new objects, you can modify existing objects and even animate them.

In last month's issue [1], we saw how to write an extension that rendered an object (a circle) in an Inkscape document. But apart from creating new objects, Inkscape extensions can also be used to modify existing objects. Let's see how this can be done be creating an extension that will generate "wobbly" animation. The idea is to take a given path – say, a piece of text – and to move its nodes around a little bit. Then save the result as a frame, move the nodes a little more, save again, and so on. When you put the frames together, it will give the impression that the text wobbles. This video shows how to do it in After Effects [2], but it seems like a lot of work for something that could be done with a relatively simple script.

Unfortunately, documentation and tutorials explaining how to create this type of script are all but nonexistent. Again the only way forward is to wade through source code and comments within code [3] to try and figure out what tools are available to achieve our ends.

What Is a Node?

Any object in Inkscape can be broken down into a bunch of paths, and paths, in turn, are made up by a bunch of nodes. So the key to modifying any object is modifying its nodes. But what is a node? You may think it is the point on a path where the path can change direction. In fact, that is just one control point, and a node is made up of three control points.

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