Improve the key events sent from the embedders to Servo

[fabricedesre]

The key events sent by the embedder to Servo are based on Glutin ones (https://doc.servo.org/src/msg/constellation_msg.rs.html#22-147), and are then mapped to DOM Key events in components/script/dom/keyboardevent.rs. This is not ideal because Glutin only has a really limited subset of possible DOM Keys (eg. most of the keys in https://w3c.github.io/uievents-key/ are missing).

Would that make sense to have the embedders do themselves the mapping from their input stack to DOM Keys instead? The other option would be to add keys to the current enum, but that doesn't seem very scalable.

@paulrouget ?

[jdm]

It does seem like a good idea to define Servo's key types in terms of what web standards describe and require embedders to communicate with Servo using those keys.

[paulrouget]

Would that make sense to have the embedders do themselves the mapping from their input stack to DOM Keys instead?

Absolutely.

[modal17]

May I look into this?

[paulrouget]

@modal17 absolutely. Let me know if you have any questions.

[paulrouget]

Do DOM key events cover enough to print all that is needed for an IME?

I'm thinking about Chinese characters, or dead keys combo. For example when I type: Option+e a, I see an accented underscore which is then replaced by á，or ni1 in Pinyin will show ni underscored then replaced with 你, or pressing lll Return will show 丿丿丿 then be replaced by彡 with a chinese keyboard. Also, navigating the temporary string with arrow keys is controlled by the input method. I'm wondering if this is all covered by https://w3c.github.io/uievents-key/#keys-composition

[fabricedesre]

Yes, what we really need is full composition support. showIME/hideIME are needed just to trigger the virtual keyboard, and then we need something similar to Gecko's nsITextInputProcessor.

[pyfisch]

I am working on this. It mostly works. I just need to refactor the built-in keyboard shortcuts.