servo: Merge #10913 - Use xi-unicode for line breaking (from mbrubeck:xi-unicode); r=pcwalton

This uses the xi-unicode crate by @raphlinus to detect line-break opportunities, replacing Servo's custom code that only detects ASCII whitespace.  xi-unicode is licensed under the Apache-2.0 license.

See mbrubeck/servo#2 for some discussion on an earlier draft of this code.  This PR implements the "search backward to find trailing whitespace" solution discussed there.

r? @pcwalton

Source-Repo: https://github.com/servo/servo
Source-Revision: fc1e4c808541ca11e25831c7c6b5cfa924945fa5

servo/components/gfx/Cargo.toml

@@ -44,6 +44,7 @@ azure = {git = "https://github.com/servo/rust-azure", features = ["plugins"]}
 layers = {git = "https://github.com/servo/rust-layers", features = ["plugins"]}
 ipc-channel = {git = "https://github.com/servo/ipc-channel"}
 webrender_traits = {git = "https://github.com/servo/webrender_traits"}
+xi-unicode = "0.0.1"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 core-foundation = "0.2"

servo/components/gfx/lib.rs

@@ -80,6 +80,7 @@ extern crate unicode_script;
 extern crate url;
 extern crate util;
 extern crate webrender_traits;
+extern crate xi_unicode;
 
 pub use paint_context::PaintContext;
 

servo/components/gfx/text/text_run.rs

@@ -12,7 +12,9 @@ use std::cmp::{Ordering, max};
 use std::slice::Iter;
 use std::sync::Arc;
 use text::glyph::{ByteIndex, GlyphStore};
+use util::str::char_is_whitespace;
 use webrender_traits;
+use xi_unicode::LineBreakIterator;
 
 thread_local! {
     static INDEX_OF_FIRST_GLYPH_RUN_CACHE: Cell<Option<(*const TextRun, ByteIndex, usize)>> =
@@ -191,73 +193,40 @@ impl<'a> TextRun {
 
     pub fn break_and_shape(font: &mut Font, text: &str, options: &ShapingOptions)
                            -> Vec<GlyphRun> {
-        // TODO(Issue #230): do a better job. See Gecko's LineBreaker.
         let mut glyphs = vec!();
-        let mut byte_i = 0;
-        let mut cur_slice_is_whitespace = false;
-        let mut byte_last_boundary = 0;
+        let mut slice = 0..0;
 
-        for ch in text.chars() {
-            // Slices alternate between whitespace and non-whitespace,
-            // representing line break opportunities.
-            let can_break_before = if cur_slice_is_whitespace {
-                match ch {
-                    ' ' | '\t' | '\n' => false,
-                    _ => {
-                        cur_slice_is_whitespace = false;
-                        true
-                    }
-                }
-            } else {
-                match ch {
-                    ' ' | '\t' | '\n' => {
-                        cur_slice_is_whitespace = true;
-                        true
-                    },
-                    _ => false
-                }
-            };
+        for (idx, _is_hard_break) in LineBreakIterator::new(text) {
+            // Extend the slice to the next UAX#14 line break opportunity.
+            slice.end = idx;
+            let word = &text[slice.clone()];
 
-            // Create a glyph store for this slice if it's nonempty.
-            if can_break_before && byte_i > byte_last_boundary {
-                let slice = &text[byte_last_boundary .. byte_i];
-                debug!("creating glyph store for slice {} (ws? {}), {} - {} in run {}",
-                        slice, !cur_slice_is_whitespace, byte_last_boundary, byte_i, text);
-
-                let mut options = *options;
-                if !cur_slice_is_whitespace {
-                    options.flags.insert(IS_WHITESPACE_SHAPING_FLAG);
-                }
+            // Split off any trailing whitespace into a separate glyph run.
+            let mut whitespace = slice.end..slice.end;
+            if let Some((i, _)) = word.char_indices().rev()
+                                     .take_while(|&(_, c)| char_is_whitespace(c)).last() {
+                whitespace.start = slice.start + i;
+                slice.end = whitespace.start;
+            }
 
+            if slice.len() > 0 {
                 glyphs.push(GlyphRun {
-                    glyph_store: font.shape_text(slice, &options),
-                    range: Range::new(ByteIndex(byte_last_boundary as isize),
-                                      ByteIndex((byte_i - byte_last_boundary) as isize)),
+                    glyph_store: font.shape_text(&text[slice.clone()], options),
+                    range: Range::new(ByteIndex(slice.start as isize),
+                                      ByteIndex(slice.len() as isize)),
                 });
-                byte_last_boundary = byte_i;
             }
-
-            byte_i = byte_i + ch.len_utf8();
-        }
-
-        // Create a glyph store for the final slice if it's nonempty.
-        if byte_i > byte_last_boundary {
-            let slice = &text[byte_last_boundary..];
-            debug!("creating glyph store for final slice {} (ws? {}), {} - {} in run {}",
-                slice, cur_slice_is_whitespace, byte_last_boundary, text.len(), text);
-
-            let mut options = *options;
-            if cur_slice_is_whitespace {
+            if whitespace.len() > 0 {
+                let mut options = options.clone();
                 options.flags.insert(IS_WHITESPACE_SHAPING_FLAG);
+                glyphs.push(GlyphRun {
+                    glyph_store: font.shape_text(&text[whitespace.clone()], &options),
+                    range: Range::new(ByteIndex(whitespace.start as isize),
+                                      ByteIndex(whitespace.len() as isize)),
+                });
             }
-
-            glyphs.push(GlyphRun {
-                glyph_store: font.shape_text(slice, &options),
-                range: Range::new(ByteIndex(byte_last_boundary as isize),
-                                  ByteIndex((byte_i - byte_last_boundary) as isize)),
-            });
+            slice.start = whitespace.end;
         }
-
         glyphs
     }
 

servo/components/servo/Cargo.lock

@@ -739,6 +739,7 @@ dependencies = [
  "url 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "webrender_traits 0.1.0 (git+https://github.com/servo/webrender_traits)",
+ "xi-unicode 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -2525,6 +2526,11 @@ dependencies = [
  "libc 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "xi-unicode"
+version = "0.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "xml-rs"
 version = "0.2.2"

servo/ports/cef/Cargo.lock

@@ -669,6 +669,7 @@ dependencies = [
  "url 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "webrender_traits 0.1.0 (git+https://github.com/servo/webrender_traits)",
+ "xi-unicode 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -2390,6 +2391,11 @@ dependencies = [
  "libc 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "xi-unicode"
+version = "0.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "xml-rs"
 version = "0.2.2"

servo/ports/gonk/Cargo.lock

@@ -672,6 +672,7 @@ dependencies = [
  "url 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "util 0.0.1",
  "webrender_traits 0.1.0 (git+https://github.com/servo/webrender_traits)",
+ "xi-unicode 0.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -2341,6 +2342,11 @@ dependencies = [
  "libc 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "xi-unicode"
+version = "0.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "xml-rs"
 version = "0.2.2"