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0324ff66f0
This commit is larger than it appears to due fanout from threading
through bidi parameters. The main changes are:
* When clustering cells, add an additional phase to resolve embedding
levels and further sub-divide a cluster based on the resolved bidi
runs; this is where we get the direction for a run and this needs
to be passed through to the shaper.
* When doing bidi, the forced cluster boundary hack that we use to
de-ligature when cursoring through text needs to be disabled,
otherwise the cursor appears to push/rotate the text in that
cluster when moving through it! We'll need to find a different
way to handle shading the cursor that eliminates the original
cursor/ligature/black issue.
* In the shaper, the logic for coalescing unresolved runs for font
fallback assumed LTR and needed to be adjusted to cluster RTL.
That meant also computing a little index of codepoint lengths.
* Added `experimental_bidi` boolean option that defaults to false.
When enabled, it activates the bidi processing phase in clustering
with a strong hint that the paragraph is LTR.
This implementation is incomplete and/or wrong for a number of cases:
* The config option should probably allow specifying the paragraph
direction hint to use by default.
* https://terminal-wg.pages.freedesktop.org/bidi/recommendation/paragraphs.html
recommends that bidi be applied to logical lines, not physical
lines (or really: ranges within physical lines) that we're doing
at the moment
* The paragraph direction hint should be overridden by cell attributes
and other escapes; see 85a6b178cf
and probably others.
However, as of this commit, if you `experimental_bidi=true` then
```
echo This is RTL -> عربي فارسی bidi
```
(that text was sourced from:
https://github.com/microsoft/terminal/issues/538#issuecomment-677017322)
then wezterm will display the text in the same order as the text
renders in Chrome for that github comment.
```
; ./target/debug/wezterm --config experimental_bidi=false ls-fonts --text "عربي فارسی ->"
LeftToRight
0 ع \u{639} x_adv=8 glyph=300 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
2 ر \u{631} x_adv=3.78125 glyph=273 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
4 ب \u{628} x_adv=4 glyph=244 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
6 ي \u{64a} x_adv=4 glyph=363 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
8 \u{20} x_adv=8 glyph=2 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
9 ف \u{641} x_adv=11 glyph=328 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
11 ا \u{627} x_adv=4 glyph=240 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
13 ر \u{631} x_adv=3.78125 glyph=273 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
15 س \u{633} x_adv=10 glyph=278 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
17 ی \u{6cc} x_adv=4 glyph=664 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
19 \u{20} x_adv=8 glyph=2 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
20 - \u{2d} x_adv=8 glyph=276 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
21 > \u{3e} x_adv=8 glyph=338 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
```
```
; ./target/debug/wezterm --config experimental_bidi=true ls-fonts --text "عربي فارسی ->"
RightToLeft
17 ی \u{6cc} x_adv=9 glyph=906 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
15 س \u{633} x_adv=10 glyph=277 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
13 ر \u{631} x_adv=4.78125 glyph=272 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
11 ا \u{627} x_adv=4 glyph=241 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
9 ف \u{641} x_adv=5 glyph=329 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
8 \u{20} x_adv=8 glyph=2 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
6 ي \u{64a} x_adv=9 glyph=904 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
4 ب \u{628} x_adv=4 glyph=243 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
2 ر \u{631} x_adv=5 glyph=273 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
0 ع \u{639} x_adv=6 glyph=301 wezterm.font(".Geeza Pro Interface", {weight="Regular", stretch="Normal", italic=false})
/System/Library/Fonts/GeezaPro.ttc index=2 variation=0, CoreText
LeftToRight
0 \u{20} x_adv=8 glyph=2 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
1 - \u{2d} x_adv=8 glyph=480 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
2 > \u{3e} x_adv=8 glyph=470 wezterm.font("Operator Mono SSm Lig", {weight="DemiLight", stretch="Normal", italic=false})
/Users/wez/.fonts/OperatorMonoSSmLig-Medium.otf, FontDirs
;
```
refs: https://github.com/wez/wezterm/issues/784
52 lines
1.8 KiB
Rust
52 lines
1.8 KiB
Rust
use wezterm_bidi::{BidiContext, Direction, ParagraphDirectionHint};
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fn main() {
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// The UBA is strongly coupled with codepoints and indices into the
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// original text, and that fans out to our API here.
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//
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// paragraph is a Vec<char>.
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let paragraph = vec!['א', 'ב', 'ג', 'a', 'b', 'c'];
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let mut context = BidiContext::new();
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// Leave it to the algorithm to determine the paragraph direction.
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// If you have some higher level understanding or override for the
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// direction, you can set `direction` accordingly.
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let hint = ParagraphDirectionHint::AutoLeftToRight;
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// Resolve the embedding levels for our paragraph.
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context.resolve_paragraph(¶graph, hint);
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/// In order to layout the text, we need to feed information to a shaper.
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/// For the purposes of example, we're sketching out a stub shaper interface
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/// here, which is essentially compatible with eg: Harfbuzz's buffer data type.
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struct ShaperBuffer {}
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impl ShaperBuffer {
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pub fn add_codepoint(&mut self, codepoint: char) {
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let _ = codepoint;
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// could call hb_buffer_add_codepoints() here
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}
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pub fn set_direction(&mut self, direction: Direction) {
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let _ = direction;
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// could call hb_buffer_set_direction() here
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}
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pub fn reset(&mut self) {}
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pub fn shape(&mut self) {}
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}
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let mut buffer = ShaperBuffer {};
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for run in context.runs() {
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buffer.reset();
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buffer.set_direction(run.direction);
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for idx in run.indices() {
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buffer.add_codepoint(paragraph[idx]);
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}
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buffer.shape();
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// Now it is up to you to use the information from the shaper
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// to decide whether and how the paragraph should be wrapped
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// into lines
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}
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}
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