Is Processing a game engine? Or is it more of a framework?
You can make games with Processing, but it’s not a game engine. There are some game libraries for Processing, though.
Processing isn’t a game engine, but you can program games in it.
You can use the library called “Green” if you dare.
If you take a look at the description on Wikipedia :
Processing is an open-source graphical library and integrated development environment (IDE) built for the electronic arts, new media art, and visual design communities with the purpose of teaching non-programmers the fundamentals of computer programming in a visual context.
So it’s considered as a Java library, not a framework (the difference). In fact, you can easily integrate it in a larger Java project with Eclipse for example.