Implement virtual selection

[Tyriar]

Handling selection manually, rather than relying on native web selection, will fix a bunch of issues that are introduced by the input helper text area, such as #68, #69 as well as:

• Double clicking on the prompt line being flaky due to focus shifting from .xterm to the text area.
• Double clicking on a URL/path to highlight the whole path (ie. don't use / and similar chars as separators)
• Selecting and copying multiple pages of the buffer
• Making the selection's line height exact so there are never any gaps between lines
• Don't drop the selection when there's a content change or viewport scroll text-selection is lost when data is written outside of the viewport #468 (comment)

[parisk]

Great. Adding this to the milestone for the next release.

[parisk]

Removed this from the milestone as most important reason for this to be there was the right-click copy/paste regression, which is addressed now in #293 without virtual selection.

[shouze]

I have a question: will it be possible then to have an automatic copy of selection into pasteboard? (as it don't seems to work at least on macOS)

[parisk]

@shouze yep this can happen by utilising the hidden text area.

if you are having trouble right now with copying and pasting in xterm.js can you open a new issue please to track what is going wrong there?

[Tyriar]

@parisk I'll probably be able to pick this up in the next couple of months

[Tyriar]

Here's what I believe needs to happen for this:

• Disable native web selection
• Create selection model that's aware of the buffer and the way it continually trims itself (may be blocked on Buffer object introduced in Add logic for reflowing lines and preserving data when resizing #609)
• Attach mouse events to selection model
  • Simple drag and drop in viewport
  • Drag beyond viewport
• Visualize selection model on screen
• Hook up copy and paste
• Tests, tests, tests

Unknowns

• How do we keep the selection themable by consumers how we do right now via ::selection?

[vincentwoo]

I don't think you'll be able to maintain perfect backwards theming functionality (you'll probably need to theme a css class, like CodeMirror does), but I don't think that should be a blocker. If necessary, you can do a major version point upgrade. It should only be a minute's work to migrate a style.

[Tyriar]

Well the selection will likely be separate from the actual text, I'm thinking of just applying classes like the xterm-color-x ones to the selection as well. It would be a regression in VS Code is the main reason I'm after this, it's great for accessibility to invert the colors.

I don't think it would be worth a major version update to change this, I'm the only one doing it AFAIK.

[parisk]

@Tyriar since selection will have it's own DOM nodes, we can just use something like .xterm-selection for styling and also fall back to ::selection styling.

Last, there is no reason to issue a new major version for this, since we do not have an official, stable theming API yet.

[Tyriar]

@parisk web selection ::selection will be disabled completely as we will manage the selection model. But yes using classes that mirror the regular color classes should work fine.