I'm primarily interested in doing this because it'll allow me to
optimize the background rendering in later diffs, but this may also make
it possible to fix some minor rendering issues.
Right now, if we draw a single-width character that overflows its cell's
bounds, and the character to the right of it has a background, that
background may cover up the first character's foreground. By drawing the
background in a separate pass, we can avoid those cases.
There's still some issues with how dirty regions are computed that makes
rendering stuff like that flaky, but this at least gets us closer to
"correct" rendering.
Other terminal emulators (e.g. alacritty) render the foreground and
background in separate passes:
https://github.com/jwilm/alacritty/blob/1b7ffea/src/renderer/mod.rs#L766
This mostly worked before, but clearColor made the assumption that the
colors were always in #RRBBGG format. See the discussion here:
https://github.com/xtermjs/xterm.js/pull/1327#issuecomment-374812842
This changes the internal representation of a color so that we hold onto
into an object containing the original css string along with an RGBA
value encoded as a 32-bit uint. clearColor can then use that RGBA
representation.
Additionally, this deduplicates some code between ColorManager and
Terminal. Terminal was generating the 256 ansi colors the same way
ColorManager was, so this just makes Terminal use the same constant.
ICharAtlasRequest and ICharAtlasConfig need almost exactly the same set
of information, so it's simpler if we just merge the two types.
As an added bonus, this also adds devicePixelRatio to the config, which
helps guarantee that we won't ever accidentally end up with an atlas
using a different pixel ratio than we need.
- Ensures that everything is only defined in one place, and everything
imports from that place.
- Moves CHAR_ATLAS_CELL_SPACING into a subdirectory of shared/ so that
CharAtlasGenerator can pull from it.
This addresses the comments on
https://github.com/xtermjs/xterm.js/pull/1307/files/454fd4bfb1ab5c9ece
The only thing `didCharSizeChange` was used for was to figure out if we
need to refresh the character atlas or not. However, `acquireCharAtlas`
already inspects the atlas owned by this terminal, and if it matches, it
avoids generating a new atlas.
So if `didCharSizeChange` is true and it's not needed, it quickly bails
out as a no-op. But if `didCharSizeChange` is false, and it was needed
(possible given the complexity of testing all of these edge cases), it
could introduce a bug.
I think it makes sense to just get rid of `didCharSizeChange`, and just
always call `acquireCharAtlas`.
I'm starting to pull some changes off of my large WIP branch/commit that
adds an alternative dynamic character atlas. We're going to need to
support multiple CharAtlas implementations, and this should make that
easier.
Benjamin Woodruff