auto merge of #2494 : bjz/servo/split-to-width, r=pcwalton

This will make removing the box splitting logic easier to implement. I am also using a `SplitInfo` struct for returning the split results, which should make the code more self-documenting. In the future the `TextRun` should not be returned, and `SplitInfo` should only require a single `CharIndex`, but one thing at a time...

@pcwalton r?

2 files changed, 85 insertions, 50 deletions

diff --git a/src/components/main/layout/box_.rs b/src/components/main/layout/box_.rs
index 125817264f1..a82699f0537 100644
--- a/src/components/main/layout/box_.rs
+++ b/src/components/main/layout/box_.rs
@@ -241,6 +241,23 @@ impl ScannedTextBoxInfo {
     }
 }
 
+#[deriving(Show)]
+pub struct SplitInfo {
+    // TODO(bjz): this should only need to be a single character index, but both values are
+    // currently needed for splitting in the `inline::try_append_*` functions.
+    pub range: Range<CharIndex>,
+    pub width: Au,
+}
+
+impl SplitInfo {
+    fn new(range: Range<CharIndex>, info: &ScannedTextBoxInfo) -> SplitInfo {
+        SplitInfo {
+            range: range,
+            width: info.run.advance_for_range(&range),
+        }
+    }
+}
+
 /// Data for an unscanned text box. Unscanned text boxes are the results of flow construction that
 /// have not yet had their width determined.
 #[deriving(Clone)]
@@ -1087,12 +1104,16 @@ impl Box {
         }
     }
 
-    /// Split box which includes new-line character.
+    /// Find the split of a box that includes a new-line character.
     ///
-    /// A return value of `None` indicates that the box could not be split.
-    /// Otherwise the split boxes are returned. The right boxe is optional due
-    /// to the possibility of it being whitespace.
-    pub fn split_by_new_line(&self) -> Option<(Box, Option<Box>)> {
+    /// A return value of `None` indicates that the box is not splittable.
+    /// Otherwise the split information is returned. The right information is
+    /// optional due to the possibility of it being whitespace.
+    //
+    // TODO(bjz): The text run should be removed in the future, but it is currently needed for
+    // the current method of box splitting in the `inline::try_append_*` functions.
+    pub fn find_split_info_by_new_line(&self)
+            -> Option<(SplitInfo, Option<SplitInfo>, Arc<owned::Box<TextRun>> /* TODO(bjz): remove */)> {
         match self.specific {
             GenericBox | IframeBox(_) | ImageBox(_) | TableBox | TableCellBox |
             TableRowBox | TableWrapperBox => None,
@@ -1107,36 +1128,32 @@ impl Box {
                                              text_box_info.range.length() - (cur_new_line_pos + CharIndex(1)));
 
                 // Left box is for left text of first founded new-line character.
-                let left_box = {
-                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), left_range);
-                    let new_metrics = new_text_box_info.run.metrics_for_range(&left_range);
-                    let mut new_box = self.transform(new_metrics.bounding_box.size, ScannedTextBox(new_text_box_info));
-                    new_box.new_line_pos = vec!();
-                    new_box
-                };
+                let left_box = SplitInfo::new(left_range, text_box_info);
 
                 // Right box is for right text of first founded new-line character.
                 let right_box = if right_range.length() > CharIndex(0) {
-                    let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), right_range);
-                    let new_metrics = new_text_box_info.run.metrics_for_range(&right_range);
-                    let mut new_box = self.transform(new_metrics.bounding_box.size, ScannedTextBox(new_text_box_info));
-                    new_box.new_line_pos = new_line_pos;
-                    Some(new_box)
+                    Some(SplitInfo::new(right_range, text_box_info))
                 } else {
                     None
                 };
 
-                Some((left_box, right_box))
+                Some((left_box, right_box, text_box_info.run.clone()))
             }
         }
     }
 
-    /// Attempts to split this box so that its width is no more than `max_width`.
+    /// Attempts to find the split positions of a text box so that its width is
+    /// no more than `max_width`.
     ///
     /// A return value of `None` indicates that the box could not be split.
-    /// Otherwise the split boxes are returned. The left and right boxes are
-    /// optional due to the possibility of them being whitespace.
-    pub fn split_to_width(&self, max_width: Au, starts_line: bool) -> Option<(Option<Box>, Option<Box>)> {
+    /// Otherwise the information pertaining to the split is returned. The left
+    /// and right split information are both optional due to the possibility of
+    /// them being whitespace.
+    //
+    // TODO(bjz): The text run should be removed in the future, but it is currently needed for
+    // the current method of box splitting in the `inline::try_append_*` functions.
+    pub fn find_split_info_for_width(&self, start: CharIndex, max_width: Au, starts_line: bool)
+            -> Option<(Option<SplitInfo>, Option<SplitInfo>, Arc<owned::Box<TextRun>> /* TODO(bjz): remove */)> {
         match self.specific {
             GenericBox | IframeBox(_) | ImageBox(_) | TableBox | TableCellBox |
             TableRowBox | TableWrapperBox => None,
@@ -1145,7 +1162,7 @@ impl Box {
             ScannedTextBox(ref text_box_info) => {
                 let mut pieces_processed_count: uint = 0;
                 let mut remaining_width: Au = max_width;
-                let mut left_range = Range::new(text_box_info.range.begin(), CharIndex(0));
+                let mut left_range = Range::new(text_box_info.range.begin() + start, CharIndex(0));
                 let mut right_range: Option<Range<CharIndex>> = None;
 
                 debug!("split_to_width: splitting text box (strlen={:u}, range={}, \
@@ -1217,25 +1234,14 @@ impl Box {
                 if (pieces_processed_count == 1 || !left_is_some) && !starts_line {
                     None
                 } else {
-                    let left_box = if left_is_some {
-                        let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), left_range);
-                        let width = new_text_box_info.run.advance_for_range(&left_range);
-                        let height = self.border_box.size.height;
-                        let size = Size2D(width, height);
-                        Some(self.transform(size, ScannedTextBox(new_text_box_info)))
+                    let left = if left_is_some {
+                        Some(SplitInfo::new(left_range, text_box_info))
                     } else {
-                        None
+                         None
                     };
+                    let right = right_range.map(|right_range| SplitInfo::new(right_range, text_box_info));
 
-                    let right_box = right_range.map(|right_range| {
-                        let new_text_box_info = ScannedTextBoxInfo::new(text_box_info.run.clone(), right_range);
-                        let width = new_text_box_info.run.advance_for_range(&right_range);
-                        let height = self.border_box.size.height;
-                        let size = Size2D(width, height);
-                        (self.transform(size, ScannedTextBox(new_text_box_info)))
-                    });
-
-                    Some((left_box, right_box))
+                    Some((left, right, text_box_info.run.clone()))
                 }
             }
         }
diff --git a/src/components/main/layout/inline.rs b/src/components/main/layout/inline.rs
index 58e21329f95..4879bd8a5e7 100644
--- a/src/components/main/layout/inline.rs
+++ b/src/components/main/layout/inline.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use css::node_style::StyledNode;
-use layout::box_::Box;
+use layout::box_::{Box, ScannedTextBox, ScannedTextBoxInfo, SplitInfo};
 use layout::context::LayoutContext;
 use layout::floats::{FloatLeft, Floats, PlacementInfo};
 use layout::flow::{BaseFlow, FlowClass, Flow, InlineFlowClass};
@@ -419,18 +419,35 @@ impl LineboxScanner {
 
     fn try_append_to_line_by_new_line(&mut self, in_box: Box) -> bool {
         if in_box.new_line_pos.len() == 0 {
-            // In case of box does not include new-line character
+                debug!("LineboxScanner: Did not find a new-line character, so pushing the box to \
+                       the line without splitting.");
             self.push_box_to_line(in_box);
             true
         } else {
-            // In case of box includes new-line character
-            match in_box.split_by_new_line() {
-                Some((left_box, Some(right_box))) => {
-                    self.push_box_to_line(left_box);
-                    self.work_list.push_front(right_box);
-                },
-                Some((left_box, None)) => {
-                    self.push_box_to_line(left_box);
+            debug!("LineboxScanner: Found a new-line character, so splitting theline.");
+            match in_box.find_split_info_by_new_line() {
+                Some((left, right, run)) => {
+                    // TODO(bjz): Remove box splitting
+                    let split_box = |split: SplitInfo| {
+                        let info = ScannedTextBoxInfo::new(run.clone(), split.range);
+                        let specific = ScannedTextBox(info);
+                        let size = Size2D(split.width, in_box.border_box.size.height);
+                        in_box.transform(size, specific)
+                    };
+
+                    debug!("LineboxScanner: Pushing the box to the left of the new-line character \
+                           to the line.");
+                    let mut left = split_box(left);
+                    left.new_line_pos = vec!();
+                    self.push_box_to_line(left);
+
+                    for right in right.move_iter() {
+                        debug!("LineboxScanner: Deferring the box to the right of the new-line \
+                               character to the line.");
+                        let mut right = split_box(right);
+                        right.new_line_pos = in_box.new_line_pos.clone();
+                        self.work_list.push_front(right);
+                    }
                 },
                 None => {
                     error!("LineboxScanner: This split case makes no sense!")
@@ -492,7 +509,19 @@ impl LineboxScanner {
         }
 
         let available_width = green_zone.width - self.pending_line.bounds.size.width;
-        match in_box.split_to_width(available_width, line_is_empty) {
+        let split = in_box.find_split_info_for_width(CharIndex(0), available_width, line_is_empty);
+        match split.map(|(left, right, run)| {
+            // TODO(bjz): Remove box splitting
+            let split_box = |split: SplitInfo| {
+                let info = ScannedTextBoxInfo::new(run.clone(), split.range);
+                let specific = ScannedTextBox(info);
+                let size = Size2D(split.width, in_box.border_box.size.height);
+                in_box.transform(size, specific)
+            };
+
+            (left.map(|x| { debug!("LineboxScanner: Left split {}", x); split_box(x) }),
+             right.map(|x| { debug!("LineboxScanner: Right split {}", x); split_box(x) }))
+        }) {
             None => {
                 debug!("LineboxScanner: Tried to split unsplittable render box! Deferring to next \
                        line. {}", in_box);