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layout: Implement overflow-wrap/word-wrap per CSS-TEXT § 6.2.

Browse source 
This property is used by approximately 55% of page loads.

To implement the line breaking behavior, the "breaking strategy" has
been cleaned up and abstracted. This should allow us to easily support
other similar properties in the future, such as `text-overflow` and
`word-break`.
This commit is contained in:
Patrick Walton 2014-12-12 22:03:00 -08:00
parent 1be7d7cced
commit 6943ddb93e
8 changed files with 356 additions and 139 deletions
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252
components/layout/fragment.rs
View file

@ -25,7 +25,7 @@ use wrapper::{TLayoutNode, ThreadSafeLayoutNode};
use geom::{Point2D, Rect, Size2D};
use gfx::display_list::OpaqueNode;
use gfx::text::glyph::CharIndex;
use gfx::text::text_run::TextRun;
use gfx::text::text_run::{TextRun, TextRunSlice};
use script_traits::UntrustedNodeAddress;
use serialize::{Encodable, Encoder};
use servo_msg::constellation_msg::{PipelineId, SubpageId};
@ -44,8 +44,8 @@ use string_cache::Atom;
use style::{ComputedValues, TElement, TNode, cascade_anonymous};
use style::computed_values::{LengthOrPercentage, LengthOrPercentageOrAuto};
use style::computed_values::{LengthOrPercentageOrNone};
use style::computed_values::{LPA_Auto, clear, position, text_align, text_decoration};
use style::computed_values::{vertical_align, white_space};
use style::computed_values::{LPA_Auto, clear, overflow_wrap, position, text_align};
use style::computed_values::{text_decoration, vertical_align, white_space};
use sync::{Arc, Mutex};
use url::Url;
@ -395,6 +395,8 @@ impl ScannedTextFragmentInfo {
}
}
/// Describes how to split a fragment. This is used during line breaking as part of the return
/// value of `find_split_info_for_inline_size()`.
#[deriving(Show)]
pub struct SplitInfo {
// TODO(bjz): this should only need to be a single character index, but both values are
@ -412,6 +414,16 @@ impl SplitInfo {
}
}
/// Describes how to split a fragment into two. This contains up to two `SplitInfo`s.
pub struct SplitResult {
/// The part of the fragment that goes on the first line.
pub inline_start: Option<SplitInfo>,
/// The part of the fragment that goes on the second line.
pub inline_end: Option<SplitInfo>,
/// The text run which is being split.
pub text_run: Arc<Box<TextRun>>,
}
/// Data for an unscanned text fragment. Unscanned text fragments are the results of flow
/// construction that have not yet had their inline-size determined.
#[deriving(Clone)]
@ -1097,104 +1109,149 @@ impl Fragment {
}
}
/// Attempts to find the split positions of a text fragment so that its inline-size is
/// no more than `max_inline-size`.
/// Attempts to find the split positions of a text fragment so that its inline-size is no more
/// than `max_inline_size`.
///
/// A return value of `None` indicates that the fragment could not be split.
/// Otherwise the information pertaining to the split is returned. The inline-start
/// and inline-end split information are both optional due to the possibility of
/// them being whitespace.
pub fn find_split_info_for_inline_size(&self,
start: CharIndex,
max_inline_size: Au,
starts_line: bool)
-> Option<(Option<SplitInfo>,
Option<SplitInfo>,
Arc<Box<TextRun>>)> {
match self.specific {
/// A return value of `None` indicates that the fragment could not be split. Otherwise the
/// information pertaining to the split is returned. The inline-start and inline-end split
/// information are both optional due to the possibility of them being whitespace.
pub fn calculate_split_position(&self, max_inline_size: Au, starts_line: bool)
-> Option<SplitResult> {
let text_fragment_info = match self.specific {
GenericFragment | IframeFragment(_) | ImageFragment(_) | TableFragment |
TableCellFragment | TableRowFragment | TableWrapperFragment | InlineBlockFragment(_) |
InlineAbsoluteHypotheticalFragment(_) => None,
InlineAbsoluteHypotheticalFragment(_) => return None,
TableColumnFragment(_) => panic!("Table column fragments do not have inline_size"),
UnscannedTextFragment(_) => {
panic!("Unscanned text fragments should have been scanned by now!")
}
ScannedTextFragment(ref text_fragment_info) => {
let mut pieces_processed_count: uint = 0;
let mut remaining_inline_size: Au = max_inline_size;
let mut inline_start_range = Range::new(text_fragment_info.range.begin() + start,
CharIndex(0));
let mut inline_end_range: Option<Range<CharIndex>> = None;
ScannedTextFragment(ref text_fragment_info) => text_fragment_info,
};
debug!("split_to_inline_size: splitting text fragment \
(strlen={}, range={}, avail_inline_size={})",
text_fragment_info.run.text.len(),
text_fragment_info.range,
max_inline_size);
for (glyphs, offset, slice_range) in text_fragment_info.run.iter_slices_for_range(
&text_fragment_info.range) {
debug!("split_to_inline_size: considering slice (offset={}, range={}, \
remain_inline_size={})",
offset,
slice_range,
remaining_inline_size);
let metrics = text_fragment_info.run.metrics_for_slice(glyphs, &slice_range);
let advance = metrics.advance_width;
let should_continue;
if advance <= remaining_inline_size || glyphs.is_whitespace() {
should_continue = true;
if starts_line && pieces_processed_count == 0 && glyphs.is_whitespace() {
debug!("split_to_inline_size: case=skipping leading trimmable whitespace");
inline_start_range.shift_by(slice_range.length());
} else {
debug!("split_to_inline_size: case=enlarging span");
remaining_inline_size = remaining_inline_size - advance;
inline_start_range.extend_by(slice_range.length());
}
} else {
// The advance is more than the remaining inline-size.
should_continue = false;
let slice_begin = offset + slice_range.begin();
if slice_begin < text_fragment_info.range.end() {
// There are still some things inline-start over at the end of the line. Create
// the inline-end chunk.
let inline_end_range_end = text_fragment_info.range.end() - slice_begin;
inline_end_range = Some(Range::new(slice_begin, inline_end_range_end));
debug!("split_to_inline_size: case=splitting remainder with inline_end range={}",
inline_end_range);
}
}
pieces_processed_count += 1;
if !should_continue {
break
}
}
let inline_start_is_some = inline_start_range.length() > CharIndex(0);
if (pieces_processed_count == 1 || !inline_start_is_some) && !starts_line {
None
} else {
let inline_start = if inline_start_is_some {
Some(SplitInfo::new(inline_start_range, &**text_fragment_info))
} else {
None
};
let inline_end = inline_end_range.map(|inline_end_range| {
SplitInfo::new(inline_end_range, &**text_fragment_info)
});
Some((inline_start, inline_end, text_fragment_info.run.clone()))
}
let mut flags = SplitOptions::empty();
if starts_line {
flags.insert(STARTS_LINE);
if self.style().get_inheritedtext().overflow_wrap == overflow_wrap::break_word {
flags.insert(RETRY_AT_CHARACTER_BOUNDARIES)
}
}
let natural_word_breaking_strategy =
text_fragment_info.run.natural_word_slices_in_range(&text_fragment_info.range);
self.calculate_split_position_using_breaking_strategy(natural_word_breaking_strategy,
max_inline_size,
flags)
}
/// A helper method that uses the breaking strategy described by `slice_iterator` (at present,
/// either natural word breaking or character breaking) to split this fragment.
fn calculate_split_position_using_breaking_strategy<'a,I>(&self,
mut slice_iterator: I,
max_inline_size: Au,
flags: SplitOptions)
-> Option<SplitResult>
where I: Iterator<TextRunSlice<'a>> {
let text_fragment_info = match self.specific {
GenericFragment | IframeFragment(_) | ImageFragment(_) | TableFragment |
TableCellFragment | TableRowFragment | TableWrapperFragment | InlineBlockFragment(_) |
InlineAbsoluteHypotheticalFragment(_) => return None,
TableColumnFragment(_) => panic!("Table column fragments do not have inline_size"),
UnscannedTextFragment(_) => {
panic!("Unscanned text fragments should have been scanned by now!")
}
ScannedTextFragment(ref text_fragment_info) => text_fragment_info,
};
let mut pieces_processed_count: uint = 0;
let mut remaining_inline_size = max_inline_size;
let mut inline_start_range = Range::new(text_fragment_info.range.begin(), CharIndex(0));
let mut inline_end_range = None;
debug!("calculate_split_position: splitting text fragment (strlen={}, range={}, \
max_inline_size={})",
text_fragment_info.run.text.len(),
text_fragment_info.range,
max_inline_size);
for slice in slice_iterator {
debug!("calculate_split_position: considering slice (offset={}, slice range={}, \
remaining_inline_size={})",
slice.offset,
slice.range,
remaining_inline_size);
let metrics = text_fragment_info.run.metrics_for_slice(slice.glyphs, &slice.range);
let advance = metrics.advance_width;
// Have we found the split point?
if advance <= remaining_inline_size || slice.glyphs.is_whitespace() {
// Keep going; we haven't found the split point yet.
if flags.contains(STARTS_LINE) && pieces_processed_count == 0 &&
slice.glyphs.is_whitespace() {
debug!("calculate_split_position: skipping leading trimmable whitespace");
inline_start_range.shift_by(slice.range.length());
} else {
debug!("split_to_inline_size: enlarging span");
remaining_inline_size = remaining_inline_size - advance;
inline_start_range.extend_by(slice.range.length());
}
pieces_processed_count += 1;
continue
}
// The advance is more than the remaining inline-size, so split here.
let slice_begin = slice.text_run_range().begin();
if slice_begin < text_fragment_info.range.end() {
// There still some things left over at the end of the line, so create the
// inline-end chunk.
let mut inline_end = slice.text_run_range();
inline_end.extend_to(text_fragment_info.range.end());
inline_end_range = Some(inline_end);
debug!("calculate_split_position: splitting remainder with inline-end range={}",
inline_end);
}
pieces_processed_count += 1;
break
}
// If we failed to find a suitable split point, we're on the verge of overflowing the line.
let inline_start_is_some = inline_start_range.length() > CharIndex(0);
if pieces_processed_count == 1 || !inline_start_is_some {
// If we've been instructed to retry at character boundaries (probably via
// `overflow-wrap: break-word`), do so.
if flags.contains(RETRY_AT_CHARACTER_BOUNDARIES) {
let character_breaking_strategy =
text_fragment_info.run.character_slices_in_range(&text_fragment_info.range);
let mut flags = flags;
flags.remove(RETRY_AT_CHARACTER_BOUNDARIES);
return self.calculate_split_position_using_breaking_strategy(
character_breaking_strategy,
max_inline_size,
flags)
}
// We aren't at the start of the line, so don't overflow. Let inline layout wrap to the
// next line instead.
if !flags.contains(STARTS_LINE) {
return None
}
}
let inline_start = if inline_start_is_some {
Some(SplitInfo::new(inline_start_range, &**text_fragment_info))
} else {
None
};
let inline_end = inline_end_range.map(|inline_end_range| {
SplitInfo::new(inline_end_range, &**text_fragment_info)
});
Some(SplitResult {
inline_start: inline_start,
inline_end: inline_end,
text_run: text_fragment_info.run.clone(),
})
}
/// Returns true if this fragment is an unscanned text fragment that consists entirely of
@ -1531,6 +1588,18 @@ bitflags! {
}
}
bitflags! {
// Various flags we can use when splitting fragments. See
// `calculate_split_position_using_breaking_strategy()`.
flags SplitOptions: u8 {
#[doc="True if this is the first fragment on the line."]
const STARTS_LINE = 0x01,
#[doc="True if we should attempt to split at character boundaries if this split fails. \
This is used to implement `overflow-wrap: break-word`."]
const RETRY_AT_CHARACTER_BOUNDARIES = 0x02
}
}
/// A top-down fragment bounds iteration handler.
pub trait FragmentBoundsIterator {
/// The operation to perform.
@ -1540,3 +1609,4 @@ pub trait FragmentBoundsIterator {
/// we skip the operation for this fragment, but continue processing siblings.
fn should_process(&mut self, fragment: &Fragment) -> bool;
}

13
components/layout/inline.rs
View file

@ -512,18 +512,17 @@ impl LineBreaker {
let available_inline_size = green_zone.inline - self.pending_line.bounds.size.inline -
indentation;
let (inline_start_fragment, inline_end_fragment) =
match fragment.find_split_info_for_inline_size(CharIndex(0),
available_inline_size,
self.pending_line_is_empty()) {
match fragment.calculate_split_position(available_inline_size,
self.pending_line_is_empty()) {
None => {
debug!("LineBreaker: fragment was unsplittable; deferring to next line: {}",
fragment);
self.work_list.push_front(fragment);
return false
}
Some((start_split_info, end_split_info, run)) => {
Some(split_result) => {
let split_fragment = |split: SplitInfo| {
let info = box ScannedTextFragmentInfo::new(run.clone(),
let info = box ScannedTextFragmentInfo::new(split_result.text_run.clone(),
split.range,
Vec::new(),
fragment.border_box.size);
@ -532,8 +531,8 @@ impl LineBreaker {
fragment.border_box.size.block);
fragment.transform(size, info)
};
(start_split_info.map(|x| split_fragment(x)),
end_split_info.map(|x| split_fragment(x)))
(split_result.inline_start.map(|x| split_fragment(x)),
split_result.inline_end.map(|x| split_fragment(x)))
}
};