Merge pull request #175 from Imberflur/stable-wrap

Fix #134 and include a test for it.

Cargo.toml

@@ -58,3 +58,6 @@ members = [
 
 [dev-dependencies]
 criterion = { version = "0.5.1", default-features = false, features = ["cargo_bench_support"] }
+
+[profile.test]
+opt-level = 1

fonts/FiraMono-LICENSE

@@ -0,0 +1,93 @@
+Digitized data copyright (c) 2012-2015, The Mozilla Foundation and Telefonica S.A.
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+This license is copied below, and is also available with a FAQ at:
+http://scripts.sil.org/OFL
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded, 
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.

src/shape.rs

@@ -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() {
+            for (i, c) in span[start_word..end_lb].char_indices().rev() {
-                if start_word + i == end_lb {
+                // TODO: Not all whitespace characters are linebreakable, e.g. 00A0 (No-break
-                    break;
+                // space)
-                } else if c.is_whitespace() {
+                // 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 one 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. {
+                                if current_visual_line.w + (word_range_width + glyph_width)
-                                    fit_x -= 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) {
+                            // TODO: What if the previous span ended with whitespace and the next
-                                // Current word causing a wrap is not whitespace, so we ignore the
+                            // span wraps a new line? Is that possible?
-                                // previous word if it's a whitespace
+                            //
-                                if previous_word.blank {
+                            // TODO: This comment it outdated, the current word can be a
-                                    trailing_space_width =
+                            // whitespace.
-                                        Some(previous_word.x_advance * font_size);
+                            //
-                                    number_of_blanks = number_of_blanks.saturating_sub(1);
+                            // Current word causing a wrap is not whitespace, so we ignore the
-                                }
+                            // previous word if it's a whitespace
-                            }
+                            let trailing_blank = span
-                            if let Some(width) = trailing_space_width {
+                                .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 one 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. {
+                                if current_visual_line.w + (word_range_width + glyph_width)
-                                    fit_x -= 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 {
+                            // Current word causing a wrap is not whitespace, so we ignore the
-                                if let Some(previous_word) = span.words.get(i - 1) {
+                            // previous word if it's a whitespace
-                                    // Current word causing a wrap is not whitespace, so we ignore the
+                            let trailing_blank = i > 0 && span.words[i - 1].blank;
-                                    // previous word if it's a whitespace
+                            if trailing_blank {
-                                    if previous_word.blank {
+                                number_of_blanks = number_of_blanks.saturating_sub(1);
-                                        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 {
                                 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,

tests/wrap_stability.rs

@@ -0,0 +1,83 @@
+use cosmic_text::{
+    fontdb, Align, Attrs, AttrsList, BidiParagraphs, Family, FontSystem, LayoutLine, ShapeLine,
+    Shaping, Weight, Wrap,
+};
+
+// Test for https://github.com/pop-os/cosmic-text/issues/134
+//
+// Being able to get the same wrapping when feeding the measured width back into ShapeLine::layout
+// as the new width limit is very useful for certain UI layout use cases.
+#[test]
+fn stable_wrap() {
+    let font_size = 18.0;
+    let attrs = AttrsList::new(
+        Attrs::new()
+            .family(Family::Name("FiraMono"))
+            .weight(Weight::MEDIUM),
+    );
+    let mut font_system =
+        FontSystem::new_with_locale_and_db("en-US".into(), fontdb::Database::new());
+    let font = std::fs::read("fonts/FiraMono-Medium.ttf").unwrap();
+    font_system.db_mut().load_font_data(font);
+
+    let mut check_wrap = |text: &_, wrap, start_width| {
+        let line = ShapeLine::new(&mut font_system, text, &attrs, Shaping::Advanced);
+
+        let layout_unbounded = line.layout(font_size, start_width, wrap, Some(Align::Left));
+        let max_width = layout_unbounded.iter().map(|l| l.w).fold(0.0, f32::max);
+        let new_limit = f32::min(start_width, max_width);
+
+        let layout_bounded = line.layout(font_size, new_limit, wrap, Some(Align::Left));
+        let bounded_max_width = layout_bounded.iter().map(|l| l.w).fold(0.0, f32::max);
+
+        // For debugging:
+        // dbg_layout_lines(text, &layout_unbounded);
+        // dbg_layout_lines(text, &layout_bounded);
+
+        assert_eq!(
+            (max_width, layout_unbounded.len()),
+            (bounded_max_width, layout_bounded.len()),
+            "Wrap \"{wrap:?}\" with text: \"{text}\"",
+        );
+        for (u, b) in layout_unbounded[1..].iter().zip(layout_bounded[1..].iter()) {
+            assert_eq!(u.w, b.w, "Wrap {wrap:?} with text: \"{text}\"",);
+        }
+    };
+
+    let hello_sample = std::fs::read_to_string("sample/hello.txt").unwrap();
+    let cases = [
+        "(6)  SomewhatBoringDisplayTransform",
+        "",
+        " ",
+        "  ",
+        "   ",
+        "       ",
+    ]
+    .into_iter()
+    // This has several cases where the line would wrap when the computed width was used as the
+    // width limit.
+    .chain(BidiParagraphs::new(&hello_sample));
+
+    for text in cases {
+        for wrap in [Wrap::Word, Wrap::Glyph] {
+            for start_width in [f32::MAX, 80.0, 198.2132, 20.0, 4.0, 300.0] {
+                check_wrap(text, wrap, start_width);
+                let with_spaces = format!("{text}            ");
+                check_wrap(&with_spaces, wrap, start_width);
+                let with_spaces_2 = format!("{text}    ");
+                check_wrap(&with_spaces_2, wrap, start_width);
+            }
+        }
+    }
+}
+
+#[allow(dead_code)]
+fn dbg_layout_lines(text: &str, lines: &[LayoutLine]) {
+    for line in lines {
+        let mut s = String::new();
+        for glyph in line.glyphs.iter() {
+            s.push_str(&text[glyph.start..glyph.end]);
+        }
+        println!("\"{s}\"");
+    }
+}