Although traditionally Cantonese speakers just use standard Chinese (mostly Traditional in my experience) for writing and reading, written Cantonese does exist as you can read about in this Wikipedia article. I'm curious as to whether there exists any input system for this written Cantonese. I specifically use Windows, but I'd be interested to know about systems for Mac and Linux as well.
If not, do most or all the characters used for written Cantonese exist in other Chinese input libraries? I ask this realizing that many of the characters in written Cantonese are simply re-purposed, but I also know that many of them are other characters with the addition of a leading 口 character and I don't know whether those exist outside of written Cantonese or not. Please enlighten me!
The preferred phonetic input method (like pinyin) for Cantonese is Jyutping (粤拼/jyut6ping3/yue4pin1 in Mandarin).
In GNU/Linux, both SCIM and (the now preferred?) IBus have packages available that add Jyutping support.
They are available for Debian, but might be hard to find for other systems. At least I have only found .deb and .rpm for ibus-jyutping, and no source.
Here's a forum thread about getting compound words to work when using Jyutping in SCIM.
There is a great system that has been created to do Cantonese Romanization to Traditional or Simplified Characters input, it is a program called NJ Star Chinese Word Processor. You can change the language to Cantonese Romanization and the output to either Traditional or Simplified and then write in the romanization and it will give you character options to choose from. The program is free and can be found here and is a great help to me.
I havent found a character that I need that I cannot find in there.