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Fix #134 and include a test for it.

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Try to ensure that using "the width computed during an unconstrained
layout" as the width constraint during a relayout produces the same
layout. This is useful for certain UI layout algorithms.

See https://github.com/pop-os/cosmic-text/issues/134

* Instead of computing the LayoutLine width from the positioned and
  aligned glyphs, we pass through width computed during line wrapping
  (unless justified alignment is used, in this case we use the old
  approach because the use case for measuring the width isn't really
  applicable to justified text since that will just expand to the
  provided width). For the produced width to later give the same
  wrapping results when passed in as the `line_width` it needs to use
  the same exact float arithmatic that was used to compute the width
  that is compared against `line_width` when making line wrapping
  choices. Passing this width through as the LayoutLine width is the
  most covenient option without making more major changse to the API.
  Nevertheless, I am imagining that if we get a dedicated measurement
  method (i.e. that doesn't do the final positioning and alignment of
  glyphs and which caches `Vec<VisualLine>`), then this width can just
  be exposed there instead of preservering it in LayoutLine.
* Incidentally, this fixes
  https://github.com/pop-os/cosmic-text/issues/169.
* Switch substraction from `fit_x` to checking whether potential
  addition to the current line width would exceed the `line_width`. This
  avoids the float error being dependent on the provided `line_width`
  value.
* When eliminating trailing space from the line width, we avoid
  backtracking with subtraction (which would not give the same exact
  value due to float error) and instead save the previous width and use
  that.
* If the previous word did not exceed the line_width, we now include a
  single blank word even if it would cross the width limit since its
  width won't be counted. This is necessary to get the same wrapping
  behavior when re-using the measured width (which doesn't count a
  single trailing blank word). Note, this whitespace logic may be
  reworked anyway if <https://github.com/pop-os/cosmic-text/issues/155>
  is addressed.
* Change tests to use `opt-level=1` to keep test runtime down.
* Add `fonts` folder for fonts used in tests.
* Fix an issue where a non-breaking whitespace was assumed to be the
  start of a section of spaces which included characters that weren't
  even whitespace.
* Add some TODOs about incongruencies between `is_whitespace`,
  justification, and line breaks.
This commit is contained in:
Imbris 2023-08-24 22:37:32 -04:00
parent 665d3d86b9
commit 91674d5a49
5 changed files with 260 additions and 48 deletions
Download patch file Download diff file Expand all files Collapse all files

129
src/shape.rs
View file

@ -569,11 +569,14 @@ impl ShapeSpan {
let mut start_word = 0;
for (end_lb, _) in unicode_linebreak::linebreaks(span) {
let mut start_lb = end_lb;
for (i, c) in span[start_word..end_lb].char_indices() {
if start_word + i == end_lb {
break;
} else if c.is_whitespace() {
for (i, c) in span[start_word..end_lb].char_indices().rev() {
// TODO: Not all whitespace characters are linebreakable, e.g. 00A0 (No-break
// space)
// https://www.unicode.org/reports/tr14/#GL
// https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
if c.is_whitespace() {
start_lb = start_word + i;
} else {
break;
}
}
@ -946,9 +949,9 @@ impl ShapeLine {
);
}
} else {
let mut fit_x = line_width;
for (span_index, span) in self.spans.iter().enumerate() {
let mut word_range_width = 0.;
let mut width_before_last_blank = 0.;
let mut number_of_blanks: u32 = 0;
// Create the word ranges that fits in a visual line
@ -957,19 +960,30 @@ impl ShapeLine {
let mut fitting_start = (span.words.len(), 0);
for (i, word) in span.words.iter().enumerate().rev() {
let word_width = font_size * word.x_advance;
if fit_x - word_width >= 0. {
// Addition in the same order used to compute the final width, so that
// relayouts with that width as the `line_width` will produce the same
// wrapping results.
if current_visual_line.w + (word_range_width + word_width)
<= line_width
// Include on blank word over the width limit since it won't be counted
// in the final width
|| (word.blank
&& (current_visual_line.w + word_range_width) <= line_width)
{
// fits
fit_x -= word_width;
word_range_width += word_width;
if word.blank {
number_of_blanks += 1;
width_before_last_blank = word_range_width;
}
word_range_width += word_width;
continue;
} else if wrap == Wrap::Glyph {
for (glyph_i, glyph) in word.glyphs.iter().enumerate().rev() {
let glyph_width = font_size * glyph.x_advance;
if fit_x - glyph_width >= 0. {
fit_x -= glyph_width;
if current_visual_line.w + (word_range_width + glyph_width)
<= line_width
{
word_range_width += glyph_width;
continue;
} else {
@ -985,30 +999,33 @@ impl ShapeLine {
current_visual_line = VisualLine::default();
number_of_blanks = 0;
fit_x = line_width - glyph_width;
word_range_width = glyph_width;
fitting_start = (i, glyph_i + 1);
}
}
} else {
// Wrap::Word
let mut trailing_space_width = None;
if let Some(previous_word) = span.words.get(i + 1) {
// Current word causing a wrap is not whitespace, so we ignore the
// previous word if it's a whitespace
if previous_word.blank {
trailing_space_width =
Some(previous_word.x_advance * font_size);
number_of_blanks = number_of_blanks.saturating_sub(1);
}
}
if let Some(width) = trailing_space_width {
// TODO: What if the previous span ended with whitespace and the next
// span wraps a new line? Is that possible?
//
// TODO: This comment it outdated, the current word can be a
// whitespace.
//
// Current word causing a wrap is not whitespace, so we ignore the
// previous word if it's a whitespace
let trailing_blank = span
.words
.get(i + 1)
.map_or(false, |previous_word| previous_word.blank);
if trailing_blank {
number_of_blanks = number_of_blanks.saturating_sub(1);
add_to_visual_line(
&mut current_visual_line,
span_index,
(i + 2, 0),
fitting_start,
word_range_width - width,
width_before_last_blank,
number_of_blanks,
);
} else {
@ -1026,11 +1043,9 @@ impl ShapeLine {
number_of_blanks = 0;
if word.blank {
fit_x = line_width;
word_range_width = 0.;
fitting_start = (i, 0);
} else {
fit_x = line_width - word_width;
word_range_width = word_width;
fitting_start = (i + 1, 0);
}
@ -1049,19 +1064,26 @@ impl ShapeLine {
let mut fitting_start = (0, 0);
for (i, word) in span.words.iter().enumerate() {
let word_width = font_size * word.x_advance;
if fit_x - word_width >= 0. {
if current_visual_line.w + (word_range_width + word_width)
<= line_width
// Include on blank word over the width limit since it won't be counted
// in the final width.
|| (word.blank
&& (current_visual_line.w + word_range_width) <= line_width)
{
// fits
fit_x -= word_width;
word_range_width += word_width;
if word.blank {
number_of_blanks += 1;
width_before_last_blank = word_range_width;
}
word_range_width += word_width;
continue;
} else if wrap == Wrap::Glyph {
for (glyph_i, glyph) in word.glyphs.iter().enumerate() {
let glyph_width = font_size * glyph.x_advance;
if fit_x - glyph_width >= 0. {
fit_x -= glyph_width;
if current_visual_line.w + (word_range_width + glyph_width)
<= line_width
{
word_range_width += glyph_width;
continue;
} else {
@ -1077,32 +1099,24 @@ impl ShapeLine {
current_visual_line = VisualLine::default();
number_of_blanks = 0;
fit_x = line_width - glyph_width;
word_range_width = glyph_width;
fitting_start = (i, glyph_i);
}
}
} else {
// Wrap::Word
let mut trailing_space_width = None;
if i > 0 {
if let Some(previous_word) = span.words.get(i - 1) {
// Current word causing a wrap is not whitespace, so we ignore the
// previous word if it's a whitespace
if previous_word.blank {
trailing_space_width =
Some(previous_word.x_advance * font_size);
number_of_blanks = number_of_blanks.saturating_sub(1);
}
}
}
if let Some(width) = trailing_space_width {
// Current word causing a wrap is not whitespace, so we ignore the
// previous word if it's a whitespace
let trailing_blank = i > 0 && span.words[i - 1].blank;
if trailing_blank {
number_of_blanks = number_of_blanks.saturating_sub(1);
add_to_visual_line(
&mut current_visual_line,
span_index,
fitting_start,
(i - 1, 0),
word_range_width - width,
width_before_last_blank,
number_of_blanks,
);
} else {
@ -1120,11 +1134,9 @@ impl ShapeLine {
number_of_blanks = 0;
if word.blank {
fit_x = line_width;
word_range_width = 0.;
fitting_start = (i + 1, 0);
} else {
fit_x = line_width - word_width;
word_range_width = word_width;
fitting_start = (i, 0);
}
@ -1166,6 +1178,19 @@ impl ShapeLine {
(Align::Center, _) => (line_width - visual_line.w) / 2.0,
(Align::End, _) => line_width - visual_line.w,
(Align::Justified, _) => {
// TODO: Only certain `is_whitespace` chars are typically expanded.
//
// https://www.unicode.org/reports/tr14/#Introduction
// > When expanding or compressing interword space according to common
// > typographical practice, only the spaces marked by U+0020 SPACE and U+00A0
// > NO-BREAK SPACE are subject to compression, and only spaces marked by U+0020
// > SPACE, U+00A0 NO-BREAK SPACE, and occasionally spaces marked by U+2009 THIN
// > SPACE are subject to expansion. All other space characters normally have
// > fixed width.
//
// (also some spaces aren't followed by potential linebreaks but they could
// still be expanded)
// Don't justify the last line in a paragraph.
if visual_line.spaces > 0 && index != number_of_visual_lines - 1 {
(line_width - visual_line.w) / visual_line.spaces as f32
@ -1335,7 +1360,15 @@ impl ShapeLine {
let mut glyphs_swap = Vec::new();
mem::swap(&mut glyphs, &mut glyphs_swap);
layout_lines.push(LayoutLine {
w: if self.rtl { start_x - x } else { x },
w: if align != Align::Justified {
visual_line.w
} else {
if self.rtl {
start_x - x
} else {
x
}
},
max_ascent: max_ascent * font_size,
max_descent: max_descent * font_size,
glyphs: glyphs_swap,