Add support for Beam, Underline cursors

[jwilm]

Notable about this implementation is it takes a different approach for
managing cursor cells that previously. The terminal Grid is now
borrowed immutably. Instead of mutating Cells in the Grid, a list is
managed within the RenderableCellsIter. The cell at the cursor location
is skipped over, and instead cells are popped off a list of cursor
cells.

It would be good in the future to share some more code between the
different cursor style implementations for populating the cursor cells
list.

Supercedes #349.
Resolves #171.

[maximbaz]

Works nicely 🙂

@jwilm out of curiosity, why did you choose symbols "▎" and "▁" for the cursor shapes? I don't know if this is right or wrong choice, I simply noticed that my monospace font (Consolas) doesn't have these glyphs and a different font is used to render these two symbols (in my case DejaVu Sans). The vertical bar looks not bad, but the underline symbol has a different character width, which looks a bit weird.

[jwilm]

@maximbaz I tried with _ and ⎸ originally, but I found them difficult to see while testing. Strange that your DejaVu Sans draws the underscore like that... I'm using the same font but haven't noticed that issue.

Maybe the beam and underscore characters should be configurable? Maybe there's some other codepoint I've overlooked that would be good for the underscore? The symbols chosen here are from the block elements block.

[NickeZ]

How do you use this? Did you forget to update the config files?

Edit: it works in neovim with :set guicursor=n-v-c:block-Cursor/lCursor-blinkon0,i-ci:ver25-Cursor/lCursor,r-cr:hor20-Cursor/lCursor.. Cheers!

[dm1try]

@NickeZ the build from master branch works for me in Neovim(0.2.1; with default guicursor option)

EDIT: added nvim version

[NickeZ]

@dm1try strange, it doesn't for me.. tried to remove the line from my init.vim and I'm back to the old block symbol in insert mode..

[net]

The sizes are wrong for my font. The | is too short, and the _ is too wide. It seems strange to use characters in the first place. Is drawing simple lines somehow not possible?

[asilvadesigns]

@jwilm this. is. awesome.

[maximbaz]

@jwilm I think you are right, the _ and | are totally impossible to notice, and I can't really find any better pair of characters for vertical bar and underscore.

However, have a look at how alacritty behaves when I set _ and | as cursor characters:

Isn't that weird, how | covers the characters? Now all the glyphs are rendered using one font, Consolas, so I would expect they fit perfectly.

I double the suggestion from @net, perhaps instead of relying on how different systems choose to select font to render ▎ and ▁, can't we just go with drawing lines directly?

[aliev]

@jwilm how to setup it for regular vim (not neovim)?

[Shougo]

@aliev :help termcap-cursor-shape

[Shougo]

For example:

  let &t_SI = "\<Esc>[6 q"
  let &t_SR = "\<Esc>[4 q"
  let &t_EI = "\<Esc>[0 q"

[aliev]

@Shougo wow! many thanks!!!

[Shougo]

I think it should be documented in Vim documentation...

[gglanzani]

I don't know if I'm doing something wrong, but I'm using Alactritty 492d1bd (August 11) combined with nvim 0.2.1 and I don't see the cursor shape changing.

I'm pretty sure it's not a neovim thing, as when using iTerm (or Terminal.app) I get different cursor shapes.

[alok]

I'm also having this issue. I'm using eb231b (from ago2 days ago).

[hale]

I had trouble with this using vim8, Alacritty and Tmux.

Fixed by removing all related settings in tmux/vim/alacritty and just installing this plugin: https://github.com/jszakmeister/vim-togglecursor