I'm having a hard time typing this without sounding like a pedantic dong(is this a rude word, or is it okay to say?), so please bear with me, it is not my intention to come off as that.
When you say keystone, do you mean actual keystoning or do you mean corner correction? Keystone is the very specific correctional feature of cheap projectors when you don't shoot the image straight on, but at a slight angle either vertically or horizontally. Corner correction is the option to take a corner of your image and place it where you want within the pixel-range of your projector. While you can "keystone"(ish) with corner correction, you can not corner correct with a keystone.
I also think you mean masking judging by your first post. Cropping can only be done from the edges, and will leave you with fewer pixels in the final image. It is essentially to physically remove rows or columns of pixels from an image. If you want to remove content diagonally, that is done with a mask.
While I absolutely agree that it is not a good experience to use the "Make Quad Layer" node to corner correct in itself - it is actually pretty nice when you have made a user interface for it. Then you can add the features you want, and have a good time mapping out your content.
Attached is a relatively simple composition using two instances of the "Make Quad Layer" to map out your content. One is used for preview and control along with handles to place your corners, the other goes to the actual output. This can of course be picked apart, modified with other options (cropping/opacity control/input selection...) and placed into a sub-composition to make for neater use and re-use. Note that this composition will reset the correction when the output window changes/moves, so do not use in production without modifying it to suit your usage. For production use, you should also implement a save system of some sort in case of restarting the composition or any unforeseen changes.
For masking, you can actually use the same approach. Just feed a quad with a black image to a layer position after the one you want to mask out, and adjust the corners of that one to suit your needs.
After trying out a few things, I now manage to compile a node successfully. However I still have an issue when I try to run a composition with the external library. I guess my understanding of how it works still isn't quite there. The error message I get inside Vuo is:
Node broken or outdated —
Undefined symbols for architecture x86_64:
"__Z12VuoData_makexPh", referenced from:
_receiveUDPMessage in composite-Ys4j2y-nIfWvb.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
From searching for the issue, it seems like there is something wrong with the build settings, but I don't understand where that lies.
Attaching the source and nodes if you find the time to look at it.
I just had this happen as well (Vuo 2.2). Paul is the composition in question stored in your user modules folder?
I noticed this happened as i loaded up Vuo and were about to continue with a composition since it wouldn't fetch data. Trying to restart Vuo the Quit option was disabled until I stopped the composition and closed the editor window. I haven't been able to reproduce this behaviour since this one instance. The computer had before this gone to sleep due to an empty battery, but Vuo was not running at the time.
What's more, fetch data still wasn't working after re-adding the file path and restarting Vuo, and still not after rebooting the computer going through the same steps. Rebuilding the composition behaved as expected so I stored the new one to compare composition files. I then noticed I somehow had managed to save it to the user modules folder. Moving the composition to the desktop made it work as expected, moving it back to the user modules folder broke the fetch data node again (after re-adding the file path).
Not sure if the two are related, or if it requires a complex sleep, start, stop procedure that in some way happened at the same time. There is at least something wonky going on with the user modules folder though.