what is a GTK theme engine?

Question

short and simple:
what is a GTK engine vs a theme etc?

Answer 1

In GTK, an engine changes the look of the widgets drawn, often to match the native widget set on a particular OS, to control properties such as widget curvature or animations. An engine is software running on your machine.

Themes are a general term for all of the artwork & the color schemes used when rendering everything you see. It's not a GTK-unique term. Two different engines could use the same theme files as input, but the final result would be rendered a bit differently. Themes are a (mostly) static collection of files.

Answer 2

Both themes and engines can be used to make your programs look different. A theme is simpler than an engine. It typically just involves creating a collection of image files that get used to construct window borders and widgets. An engine is like a plugin to a web browser that actually runs new code to generate the borders and widgets. Engines are more complex to create, but this allows them to create fancier effects.

Answer 3

The theme engine is the display backend that uses a theme to style windows.