GEGL Plug-Ins for GIMP. Part Three: Writing C Plug-Ins

This is the third in a series of articles about GEGL plug-ins for the GIMP image editor. See also part one and part two for more about GEGL plug-ins and using them from inside GIMP.

You don’t need to know C to use this article, or be a programmer.

Note: you can also use GEGL plug-ins outside of GIMP, e.g. in the gegl command-line program and maybe even in GNOME-Photos, unless you use GIMP-specific features such as calling other GEGL operations that GIMP provides.

Why do it?

GEGL Plug-ins are super easy to use in GIMP with on-canvas preview, and you can even save and load settings. They are in the C programming language and are nice and fast, sometimes taking advantage of your graphics card or multi-threading.

Although you can write scripts for GIMP in Python, Schema, JavaScript, Lua, and maybe more languages, those scripts don’t get a preview at all, or just get a tiny one in a  pop-up window.

GEGL plug-ins can also be used as part of more complex GEGL graphs, like building blocks.

How hard is it?

Someone who hasn’t written any C before and isn’t a programmer can translate the GEGL Chain syntax shown in part two into C, with a little practice. You may need help from a C programmer if you get errors or get stuck. This article mentions some of the common errors, though.

Allow about an hour to turn a GEGL chain into a C plug-in the first time, and about another hour to get it to compile if you haven't done that before.

GEGL Plug-Ins for GIMP. Part Two: GEGL Graph

In Part One of this article we looked at running GEGL plug-ins as live filters, using the GEGL Operation dialogue. GEGL plug-ins are super cool and have live on-canvas preview. Now in Part Two we’ll take it to the next level and look at the more powerful GEGL Graph GIMP plug-in.

GEGL Plug-Ins for GIMP. Part One: Using GEGL Plug-Ins

If you don’t know about GEGL plug-ins for GIMP, you’ve been missing out. There’s not many of them, but that’s changing with more people writing them. And they offer flexibility and power you didn’t know GIMP had. 

This three-part article first shows some of the gegl plug-ins that are available, and how to get them going (it’s easy, don’t worry)

Then, in part two, we’ll look at the GEGL Graph plug-in you can use as a way to make your own super-powerful filters.

Finally, we build up to writing a simple GEGL plug-in in C, written for people without a maths or programming background.