Add Piet Lang

[Bubbler-4]

Piet is a classic esolang where the source code is an image file. It has a unique routing semantics, minimalistic but reasonable set of commands, and a lot of metagolfing potential.

Some of the obstacles for adding this language to code.golf include:

• [ ] How to score the source code. Classically, the size of a Piet source code is measured in codels (number of pixels in the image, i.e. width x height) but the standard for code golfing is in bytes. It is shown that an encoding that enables codels==bytes can be designed, but it allows some golfing below the codel count. Should we devise an encoding that enforces codels==bytes? Or would people be fine with a more 2Dlang-like encoding, where each newline costs 1 extra byte and some unused cells (black codels) at end-of-line may save bytes?
• [ ] We need a standards-conforming interpreter that can accept source code from stdin. npiet is almost standard-conforming, but it doesn't correctly handle "looping entirely within white region ends the program".
• [ ] Can Piet solve all holes currently up on code.golf? It has first-class support of basic arithmetic, but the only tool for random access is the roll command, which can be quite slow when you need to keep and manipulate large amount of data.
• [ ] Logo. I guess something shaped like one of Mondrian's works would work well.

I want to mainly discuss about encoding of source code before actually working on adding it.

[Bubbler-4]

For anyone who hasn't tried Piet before, you can play with it in my online interpreter.

[MichalMarsalek]

How about chars score = number of codels, bytes score = size of a PNG encoding the image?

Who says that the encoding used for measuring the byte score must always be UTF8? That makes sense for languages whose source is naturally represented as text, but that's not the case for Piet. Just as UTF8 is de facto standard for lossless text encoding, PNG is de facto standard for lossless image encoding.

Regarding the UI, I have no idea how hard it would be to implement an image editor/if there are easy to use js libraries, but imo it wouldn't be a big deal if the "editor" was just a read-only view of the image and you could update it by copy pasting.

[Bubbler-4]

I'd like to keep submission to some text format because

• it's a burden to implement and maintain a submission format that will likely only be used for one language
• scoring is simple and clear (there are many tricks to golf PNG format and I doubt you want it)
• I hate my corporate firewall that allows submitting text but not files

[MichalMarsalek]

Whatever the format, the chars score should be the number of codels. We could enforce a text format where byte=codel (the one you linked + error when lines do not all have equal length), but since we do have 2 scoring methods on the site, I'd say just leave it raw for the byte scoring (endlines cause extra byte, but black codels at the end of line save bytes).