Upstream Chrome on iOS source code [10/11].

ios/chrome/browser/ui/util/manual_text_framer.mm

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/util/manual_text_framer.h"
+
+#import <UIKit/UIKit.h>
+
+#include "base/i18n/rtl.h"
+#include "base/logging.h"
+#include "base/mac/foundation_util.h"
+#include "base/mac/scoped_nsobject.h"
+#import "ios/chrome/browser/ui/util/core_text_util.h"
+#import "ios/chrome/browser/ui/util/text_frame.h"
+#import "ios/chrome/browser/ui/util/unicode_util.h"
+
+// NOTE: When RTL text is laid out into glyph runs, the glyphs appear in the
+// visual order in which they appear on screen.  In other words, the glyphs are
+// arranged in the reverse order of their corresponding characters in the
+// original string.
+
+namespace {
+// Aligns |value| to the nearest pixel value, rounding by the function indicated
+// by |function|.  AlignmentFunction::CEIL should be used to align size values,
+// while AlignmentFunction::FLOOR should be used to align location values.
+enum class AlignmentFunction : short { CEIL = 0, FLOOR };
+CGFloat AlignValueToPixel(CGFloat value, AlignmentFunction function) {
+  static CGFloat scale = [[UIScreen mainScreen] scale];
+  return function == AlignmentFunction::CEIL ? ceil(value * scale) / scale
+                                             : floor(value * scale) / scale;
+}
+
+// Returns an NSArray of NSAttributedStrings corresponding to newline-separated
+// paragraphs within |string|.
+NSArray* GetParagraphStringsForString(NSAttributedString* string) {
+  NSMutableArray* paragraph_strings = [NSMutableArray array];
+  NSCharacterSet* newline_char_set = [NSCharacterSet newlineCharacterSet];
+  NSUInteger string_length = string.string.length;
+  NSRange remaining_range = NSMakeRange(0, string_length);
+  while (remaining_range.location < string_length) {
+    NSRange newline_range =
+        [string.string rangeOfCharacterFromSet:newline_char_set
+                                       options:0
+                                         range:remaining_range];
+    NSRange paragraph_range = NSMakeRange(0, 0);
+    if (newline_range.location == NSNotFound) {
+      // There's no newline in the remaining portion of the string.
+      paragraph_range = remaining_range;
+      remaining_range = NSMakeRange(string_length, 0);
+    } else {
+      // A newline character was encountered.  Compute approximate text lines
+      // for the substring within |remaining_range| up to the newline.
+      NSUInteger newline_end = newline_range.location + newline_range.length;
+      paragraph_range = NSMakeRange(remaining_range.location,
+                                    newline_end - remaining_range.location);
+      remaining_range.location = newline_end;
+      remaining_range.length = string_length - remaining_range.location;
+    }
+    // Create an attributed substring for the current paragraph and add it to
+    // |paragraphs|.
+    [paragraph_strings
+        addObject:[string attributedSubstringFromRange:paragraph_range]];
+  }
+  return paragraph_strings;
+}
+}  // namespace
+
+#pragma mark - ManualTextFrame
+
+// A TextFrame implementation that is manually created by ManualTextFramer.
+@interface ManualTextFrame : NSObject<TextFrame> {
+  // Backing objects for properties of the same name.
+  base::scoped_nsobject<NSAttributedString> _string;
+  base::scoped_nsobject<NSMutableArray> _lines;
+}
+
+// Designated initializer.
+- (instancetype)initWithString:(NSAttributedString*)string
+                      inBounds:(CGRect)bounds NS_DESIGNATED_INITIALIZER;
+- (instancetype)init NS_UNAVAILABLE;
+
+// Creates a FramedLine out of |line|, |stringRange|, and |origin|, then adds it
+// to |lines|.
+- (void)addFramedLineWithLine:(CTLineRef)line
+                  stringRange:(NSRange)stringRange
+                       origin:(CGPoint)origin;
+
+// Redefine property as readwrite.
+@property(nonatomic, readwrite) NSRange framedRange;
+
+@end
+
+@implementation ManualTextFrame
+
+@synthesize framedRange = _framedRange;
+@synthesize bounds = _bounds;
+
+- (instancetype)initWithString:(NSAttributedString*)string
+                      inBounds:(CGRect)bounds {
+  if ((self = [super init])) {
+    DCHECK(string.string.length);
+    _string.reset([string retain]);
+    _bounds = bounds;
+    _lines.reset([[NSMutableArray alloc] init]);
+  }
+  return self;
+}
+
+#pragma mark Accessors
+
+- (NSAttributedString*)string {
+  return _string.get();
+}
+
+- (NSArray*)lines {
+  return _lines.get();
+}
+
+#pragma mark Private
+
+- (void)addFramedLineWithLine:(CTLineRef)line
+                  stringRange:(NSRange)stringRange
+                       origin:(CGPoint)origin {
+  base::scoped_nsobject<FramedLine> framedLine([[FramedLine alloc]
+      initWithLine:line
+       stringRange:stringRange
+            origin:origin]);
+  [_lines addObject:framedLine];
+}
+
+@end
+
+#pragma mark - ManualTextFramer Private Interface
+
+@interface ManualTextFramer () {
+  // Backing objects for properties of the same name.
+  base::scoped_nsobject<NSAttributedString> _string;
+  base::scoped_nsobject<ManualTextFrame> _manualTextFrame;
+}
+
+// The string passed upon initialization.
+@property(nonatomic, readonly) NSAttributedString* string;
+
+// The bounds passed upon initialization.
+@property(nonatomic, readonly) CGRect bounds;
+
+// The width of the bounds passed upon initialization.
+@property(nonatomic, readonly) CGFloat boundingWidth;
+
+// The remaining height into which text can be framed.
+@property(nonatomic, assign) CGFloat remainingHeight;
+
+// The text frame constructed by |-frameText|.
+@property(nonatomic, readonly) ManualTextFrame* manualTextFrame;
+
+// Creates a ManualTextFrame and assigns it to |_manualTextFrame|.  Returns YES
+// if a new text frame was successfully created.
+- (BOOL)setupManualTextFrame;
+
+@end
+
+#pragma mark - ParagraphFramer
+
+// ManualTextFramer subclass that frames a single paragraph.  A paragraph is
+// defined as an NSAttributedString which contains either zero newlines or one
+// newline as its last character.
+@interface ParagraphFramer : ManualTextFramer {
+  // Backing objects for properties of the same name.
+  base::ScopedCFTypeRef<CTLineRef> _line;
+  base::scoped_nsobject<NSCharacterSet> _lineEndSet;
+}
+
+// The CTLine created from |string|.
+@property(nonatomic, readonly) CTLineRef line;
+
+// The effective text alignment for |line|.
+@property(nonatomic, readonly) NSTextAlignment effectiveAlignment;
+
+// Character set containing characters that are appropriate for line endings.
+// These characters include whitespaces and newlines (denoting a word boundary),
+// in addition to line-ending characters like hyphens, em dashes, and en dashes.
+@property(nonatomic, readonly) NSCharacterSet* lineEndSet;
+
+// The index of the current run that is being framed.  Setting |runIdx| also
+// updates |currentRun| and |currentGlyphCount|.
+@property(nonatomic, assign) CFIndex runIdx;
+
+// The CTRun corresponding with |runIdx| in |line|.
+@property(nonatomic, readonly) CTRunRef currentRun;
+
+// The glyph count in |currentRun|.
+@property(nonatomic, readonly) CFIndex currentGlyphCount;
+
+// The number of glyphs in |currentRun| that have been successfully framed.
+@property(nonatomic, assign) CFIndex framedGlyphCount;
+
+// The range in |string| that has successfully been framed for the current line.
+@property(nonatomic, assign) NSRange currentLineRange;
+
+// The width of the typographic bounds for the glyphs framed on the current
+// line.  This is the width of the substring of |string| corresponding to
+// |currentLineRange|.
+@property(nonatomic, assign) CGFloat currentLineWidth;
+
+// The width of the trailing whitespace for the current line.  This whitespace
+// is not counted against the line width if it's the end of the line, but needs
+// to be added in if non-whitespace characters from subsequent runs fit on the
+// same line.
+@property(nonatomic, assign) CGFloat currentWhitespaceWidth;
+
+// Whether the paragraph's writing direction is in RTL.
+@property(nonatomic, readonly) BOOL isRTL;
+
+// Either 1 or -1 depending on |isRTL|.
+@property(nonatomic, readonly) CFIndex incrementAmount;
+
+// Glyphs are laid out differently for RTL and LTR languages (see note at top of
+// file).  These functions return a range with |range|'s length incremented or
+// decremented and an updated location that would include the next glyph in the
+// trailing direction.
+- (CFRange)incrementRange:(CFRange)range byAmount:(CFIndex)amount;
+- (CFRange)incrementRange:(CFRange)range;
+- (CFRange)decrementRange:(CFRange)range;
+
+// Updates |range| such that its trailing glyph index is |trailingGlyphIdx|.
+- (CFRange)updateRange:(CFRange)range
+    forTrailingGlyphIdx:(CFIndex)trailingGlyphIdx;
+
+// Returns the index of the trailing glyph in |range| for |currentRun|.
+- (CFIndex)trailingGlyphIdxForRange:(CFRange)range;
+
+// Returns the index of the leading or trailing glyph in |currentRun|.
+- (CFIndex)trailingGlyphIdxForCurrentRun;
+
+// Manually frames the glyphs in |currentRun| following |framedGlyphCount|.
+// This function updates |framedGlyphCount|, |currentLineWidth|, and
+// |currentLineRange|.
+- (void)frameCurrentRun;
+
+// Returns the character associated with the glyph at |glyphIdx| in
+// |currentRun|.
+- (unichar)charForGlyphAtIdx:(CFIndex)glyphIdx;
+
+// Returns the index within the original string corresponding to the glyph at
+// |glyphIdx| in |currentRun|.
+- (CFIndex)stringIdxForGlyphAtIdx:(CFIndex)glyphIdx;
+
+// Returns YES if |runIdx| is within the range of |line|'s glyph runs array.
+- (BOOL)runIdxIsValid:(CFIndex)runIdx;
+
+// Returns YES if |glyphIdx| is within [0, |currentGlyphCount|).
+- (BOOL)glyphIdxIsValid:(CFIndex)glyphIdx;
+
+// Creates a line from |currentLineRange| and adds it to |lines|.
+- (void)addCurrentLine;
+
+// Returns the baselines origin for the current line.  This function depends on
+// |currentLineRange|, |currentLineWidth|, and |remainingHeight|, and must be
+// called before updating those bookkeeping variables when adding the line.
+- (CGPoint)originForCurrentLine;
+@end
+
+@implementation ParagraphFramer
+
+@synthesize effectiveAlignment = _effectiveTextAlignment;
+@synthesize runIdx = _runIdx;
+@synthesize currentRun = _currentRun;
+@synthesize currentGlyphCount = _currentGlyphCount;
+@synthesize framedGlyphCount = _framedGlyphCount;
+@synthesize currentLineRange = _currentLineRange;
+@synthesize currentLineWidth = _currentLineWidth;
+@synthesize currentWhitespaceWidth = _currentWhitespaceWidth;
+@synthesize isRTL = _isRTL;
+
+- (instancetype)initWithString:(NSAttributedString*)string
+                      inBounds:(CGRect)bounds {
+  if ((self = [super initWithString:string inBounds:bounds])) {
+    NSRange newlineRange = [string.string
+        rangeOfCharacterFromSet:[NSCharacterSet newlineCharacterSet]];
+    DCHECK(newlineRange.location == NSNotFound ||
+           newlineRange.location == string.string.length - 1);
+    CTLineRef line =
+        CTLineCreateWithAttributedString(base::mac::NSToCFCast(string));
+    _line.reset(line);
+    _effectiveTextAlignment = core_text_util::GetEffectiveTextAlignment(string);
+    NSWritingDirection direction =
+        core_text_util::GetEffectiveWritingDirection(string);
+    _isRTL = direction == NSWritingDirectionRightToLeft;
+  }
+  return self;
+}
+
+- (void)frameText {
+  if (![self setupManualTextFrame])
+    return;
+  self.runIdx =
+      self.isRTL ? CFArrayGetCount(CTLineGetGlyphRuns(self.line)) - 1 : 0;
+  while (self.currentRun) {
+    NSRange runStringRange =
+        core_text_util::GetStringRangeForRun(self.currentRun);
+    DCHECK_NE(runStringRange.location, static_cast<NSUInteger>(NSNotFound));
+    DCHECK_NE(runStringRange.length, 0U);
+    CGFloat runLineHeight =
+        core_text_util::GetLineHeight(self.string, runStringRange);
+    // Count of the number of times the framing process (-frameCurrentRun) has
+    // "stalled" -- run without changing the total number of glyphs framed. In
+    // some cases the process may stall once at the end of a run, but if it
+    // stalls twice, it won't make any further progress and should halt.
+    NSUInteger stallCount = 0;
+    // Loop as long as framed glyph count is less that the total glyph count,
+    // and the framer is making progress.
+    while (self.framedGlyphCount < self.currentGlyphCount && stallCount < 2U) {
+      // Stop framing glyphs if there is not enough vertical space for the run.
+      if (self.remainingHeight < runLineHeight)
+        break;
+      CFIndex initialFramedGlyphCount = self.framedGlyphCount;
+      [self frameCurrentRun];
+      if (self.framedGlyphCount == initialFramedGlyphCount)
+        stallCount++;
+      if (self.framedGlyphCount < self.currentGlyphCount) {
+        // The entire run didn't fit onto the current line, so create a CTLine
+        // from |currentLineRange| and add it to |lines|.
+        [self addCurrentLine];
+      }
+    }
+    self.runIdx += self.incrementAmount;
+  }
+  // Add the final line.
+  [self addCurrentLine];
+  // Update |manualTextFrame|'s |framedRange|.
+  self.manualTextFrame.framedRange =
+      NSMakeRange(0, self.currentLineRange.location);
+}
+
+#pragma mark Accessors
+
+- (CTLineRef)line {
+  return _line.get();
+}
+
+- (NSCharacterSet*)lineEndSet {
+  if (!_lineEndSet) {
+    NSMutableCharacterSet* lineEndSet =
+        [NSMutableCharacterSet whitespaceAndNewlineCharacterSet];
+    [lineEndSet addCharactersInString:@"-\u2013\u2014"];
+    _lineEndSet.reset([lineEndSet retain]);
+  }
+  return _lineEndSet;
+}
+
+- (void)setRunIdx:(CFIndex)runIdx {
+  _runIdx = runIdx;
+  self.framedGlyphCount = 0;
+  if ([self runIdxIsValid:runIdx]) {
+    NSArray* runs = base::mac::CFToNSCast(CTLineGetGlyphRuns(self.line));
+    _currentRun = static_cast<CTRunRef>(runs[_runIdx]);
+    _currentGlyphCount = CTRunGetGlyphCount(self.currentRun);
+  } else {
+    _currentRun = nullptr;
+    _currentGlyphCount = 0;
+  }
+}
+
+- (CFIndex)incrementAmount {
+  return self.isRTL ? -1 : 1;
+}
+
+#pragma mark Private
+
+- (CFRange)incrementRange:(CFRange)range byAmount:(CFIndex)amount {
+  CFRange incrementedRange = range;
+  incrementedRange.length += amount;
+  if (self.isRTL)
+    incrementedRange.location += self.incrementAmount * amount;
+  return incrementedRange;
+}
+
+- (CFRange)incrementRange:(CFRange)range {
+  return [self incrementRange:range byAmount:1];
+}
+
+- (CFRange)decrementRange:(CFRange)range {
+  return [self incrementRange:range byAmount:-1];
+}
+
+- (CFRange)updateRange:(CFRange)range
+    forTrailingGlyphIdx:(CFIndex)trailingGlyphIdx {
+  DCHECK(self.isRTL ? trailingGlyphIdx <= range.location + range.length
+                    : trailingGlyphIdx >= range.location);
+  DCHECK([self glyphIdxIsValid:trailingGlyphIdx]);
+  CFIndex currentTrailingGlyphIdx = [self trailingGlyphIdxForRange:range];
+  CFIndex updateAmount = self.isRTL
+                             ? currentTrailingGlyphIdx - trailingGlyphIdx
+                             : trailingGlyphIdx - currentTrailingGlyphIdx;
+  return [self incrementRange:range byAmount:updateAmount];
+}
+
+- (CFIndex)trailingGlyphIdxForRange:(CFRange)range {
+  if (self.isRTL)
+    return range.location;
+  return range.location + range.length - 1;
+}
+
+- (CFIndex)trailingGlyphIdxForCurrentRun {
+  return self.isRTL ? 0 : self.currentGlyphCount - 1;
+}
+
+- (void)frameCurrentRun {
+  DCHECK(self.currentRun);
+  DCHECK_LT(self.framedGlyphCount, self.currentGlyphCount);
+  DCHECK_LT(self.currentLineWidth, self.boundingWidth);
+
+  // Calculate the range that will fit in the remaining portion of the line.
+  NSCharacterSet* whitespaceSet =
+      [NSCharacterSet whitespaceAndNewlineCharacterSet];
+  CFIndex startGlyphIdx = self.isRTL
+                              ? self.currentGlyphCount - self.framedGlyphCount
+                              : self.framedGlyphCount;
+  CFRange remainingRunRange =
+      CFRangeMake(self.isRTL ? 0 : startGlyphIdx,
+                  self.currentGlyphCount - self.framedGlyphCount);
+  CFRange range = CFRangeMake(startGlyphIdx, 0);
+  while (remainingRunRange.length > 0) {
+    // Find the range for the next word that can be added to the line.  If no
+    // delimiters were found, frame the rest of the run.
+    CFIndex delimIdx = core_text_util::GetGlyphIdxForCharInSet(
+        self.currentRun, remainingRunRange, self.string, self.lineEndSet);
+    if (delimIdx == kCFNotFound)
+      delimIdx = [self trailingGlyphIdxForCurrentRun];
+    CFRange wordGlyphRange =
+        [self updateRange:remainingRunRange forTrailingGlyphIdx:delimIdx];
+    CFIndex wordFramedGlyphCount = wordGlyphRange.length;
+    // Trim any whitespace and record its width.
+    CGFloat wordTrailingWhitespaceWidth = 0.0;
+    if ([whitespaceSet characterIsMember:[self charForGlyphAtIdx:delimIdx]]) {
+      wordTrailingWhitespaceWidth =
+          core_text_util::GetGlyphWidth(self.currentRun, delimIdx);
+      wordGlyphRange = [self decrementRange:wordGlyphRange];
+    }
+    // Check if the word will fit on the line.
+    CGFloat wordWidth =
+        core_text_util::GetRunWidthWithRange(self.currentRun, wordGlyphRange);
+    CGFloat cumulativeLineWidth =
+        self.currentLineWidth + self.currentWhitespaceWidth + wordWidth;
+    if (cumulativeLineWidth <= self.boundingWidth) {
+      // The word at |wordGlyphRange| fits on the line.
+      self.currentLineWidth = cumulativeLineWidth;
+      self.framedGlyphCount += wordFramedGlyphCount;
+      self.currentWhitespaceWidth = wordTrailingWhitespaceWidth;
+      remainingRunRange.length -= wordFramedGlyphCount;
+      if (!self.isRTL)
+        remainingRunRange.location += wordFramedGlyphCount;
+      range = [self incrementRange:range byAmount:wordFramedGlyphCount];
+    } else {
+      break;
+    }
+  }
+  // Early return if no glyphs were framed.
+  if (!range.length)
+    return;
+  // Use the string index of the next glyph to determine the string range for
+  // the current line, since a glyph may correspond with multiple characters
+  // when ligatures are used.
+  CFIndex nextGlyphIdx =
+      [self trailingGlyphIdxForRange:range] + self.incrementAmount;
+  CFIndex nextGlyphStringIdx;
+  if ([self glyphIdxIsValid:nextGlyphIdx]) {
+    nextGlyphStringIdx = [self stringIdxForGlyphAtIdx:nextGlyphIdx];
+  } else {
+    CFRange runStringRange = CTRunGetStringRange(self.currentRun);
+    nextGlyphStringIdx = runStringRange.location + runStringRange.length;
+  }
+  self.currentLineRange =
+      NSMakeRange(self.currentLineRange.location,
+                  nextGlyphStringIdx - self.currentLineRange.location);
+}
+
+- (unichar)charForGlyphAtIdx:(CFIndex)glyphIdx {
+  DCHECK([self glyphIdxIsValid:glyphIdx]);
+  return [self.string.string
+      characterAtIndex:[self stringIdxForGlyphAtIdx:glyphIdx]];
+}
+
+- (CFIndex)stringIdxForGlyphAtIdx:(CFIndex)glyphIdx {
+  DCHECK([self glyphIdxIsValid:glyphIdx]);
+  CFIndex stringIdx = 0;
+  CTRunGetStringIndices(self.currentRun, CFRangeMake(glyphIdx, 1), &stringIdx);
+  return stringIdx;
+}
+
+- (BOOL)runIdxIsValid:(CFIndex)runIdx {
+  NSArray* runs = base::mac::CFToNSCast(CTLineGetGlyphRuns(self.line));
+  return runIdx >= 0 && runIdx < static_cast<CFIndex>(runs.count);
+}
+
+- (BOOL)glyphIdxIsValid:(CFIndex)glyphIdx {
+  return glyphIdx >= 0 && glyphIdx < self.currentGlyphCount;
+}
+
+- (void)addCurrentLine {
+  // Don't attempt to add a line if |currentLineRange| is empty.
+  if (!self.currentLineRange.length)
+    return;
+  // Add the new line and its corresponding string range and baseline origin.
+  NSAttributedString* currentLineString =
+      [self.string attributedSubstringFromRange:self.currentLineRange];
+  CTLineRef currentLine = CTLineCreateWithAttributedString(
+      base::mac::NSToCFCast(currentLineString));
+  [self.manualTextFrame addFramedLineWithLine:currentLine
+                                  stringRange:self.currentLineRange
+                                       origin:[self originForCurrentLine]];
+  CFRelease(currentLine);
+  // Update bookkeeping variables for next line.
+  CGFloat usedHeight =
+      core_text_util::GetLineHeight(self.string, self.currentLineRange) +
+      core_text_util::GetLineSpacing(self.string, self.currentLineRange);
+  self.currentLineRange = NSMakeRange(
+      self.currentLineRange.location + self.currentLineRange.length, 0);
+  self.currentLineWidth = 0;
+  self.currentWhitespaceWidth = 0;
+  self.remainingHeight -= usedHeight;
+}
+
+- (CGPoint)originForCurrentLine {
+  CGPoint origin = CGPointZero;
+  CGFloat alignedWidth =
+      AlignValueToPixel(self.currentLineWidth, AlignmentFunction::CEIL);
+  switch (self.effectiveAlignment) {
+    case NSTextAlignmentLeft:
+      // Left-aligned lines begin at 0.0.
+      break;
+    case NSTextAlignmentRight:
+      origin.x = AlignValueToPixel(self.boundingWidth - alignedWidth,
+                                   AlignmentFunction::FLOOR);
+      break;
+    case NSTextAlignmentCenter:
+      origin.x = AlignValueToPixel((self.boundingWidth - alignedWidth) / 2.0,
+                                   AlignmentFunction::FLOOR);
+      break;
+    default:
+      // Only left, right, and center effective alignment is supported.
+      NOTREACHED();
+      break;
+  }
+  UIFont* font = [self.string attribute:NSFontAttributeName
+                                atIndex:self.currentLineRange.location
+                         effectiveRange:nullptr];
+  CGFloat lineHeight =
+      core_text_util::GetLineHeight(self.string, self.currentLineRange);
+  origin.y =
+      AlignValueToPixel(self.remainingHeight - lineHeight - font.descender,
+                        AlignmentFunction::FLOOR);
+  return origin;
+}
+
+@end
+
+#pragma mark - ManualTextFramer
+
+@implementation ManualTextFramer
+
+@synthesize bounds = _bounds;
+@synthesize boundingWidth = _boundingWidth;
+@synthesize remainingHeight = _remainingHeight;
+
+- (instancetype)initWithString:(NSAttributedString*)string
+                      inBounds:(CGRect)bounds {
+  if ((self = [super init])) {
+    DCHECK(string.string.length);
+    _string.reset([string retain]);
+    _bounds = bounds;
+    _boundingWidth = CGRectGetWidth(bounds);
+    _remainingHeight = CGRectGetHeight(bounds);
+  }
+  return self;
+}
+
+- (void)frameText {
+  if (![self setupManualTextFrame])
+    return;
+  NSRange framedRange = NSMakeRange(0, 0);
+  NSArray* paragraphs = GetParagraphStringsForString(self.string);
+  NSUInteger stringRangeOffset = 0;
+  for (NSAttributedString* paragraph in paragraphs) {
+    // Frame each paragraph using a ParagraphFramer, then update bookkeeping
+    // variables for the top-level ManualTextFramer.
+    CGRect remainingBounds =
+        CGRectMake(0, 0, self.boundingWidth, self.remainingHeight);
+    base::scoped_nsobject<ParagraphFramer> framer([[ParagraphFramer alloc]
+        initWithString:paragraph
+              inBounds:remainingBounds]);
+    [framer frameText];
+    id<TextFrame> frame = [framer textFrame];
+    DCHECK(frame);
+    framedRange.length += frame.framedRange.length;
+    CGFloat paragraphHeight = 0.0;
+    for (FramedLine* line in frame.lines) {
+      NSRange lineRange = line.stringRange;
+      lineRange.location += stringRangeOffset;
+      [self.manualTextFrame addFramedLineWithLine:line.line
+                                      stringRange:lineRange
+                                           origin:line.origin];
+      paragraphHeight += core_text_util::GetLineHeight(self.string, lineRange) +
+                         core_text_util::GetLineSpacing(self.string, lineRange);
+    }
+    self.remainingHeight -= paragraphHeight;
+    stringRangeOffset += paragraph.string.length;
+  }
+  self.manualTextFrame.framedRange = framedRange;
+}
+
+#pragma mark Accessors
+
+- (NSAttributedString*)string {
+  return _string.get();
+}
+
+- (ManualTextFrame*)manualTextFrame {
+  return _manualTextFrame.get();
+}
+
+- (id<TextFrame>)textFrame {
+  return _manualTextFrame.get();
+}
+
+#pragma mark Private
+
+- (BOOL)setupManualTextFrame {
+  if (_manualTextFrame)
+    return NO;
+  _manualTextFrame.reset([[ManualTextFrame alloc] initWithString:self.string
+                                                        inBounds:self.bounds]);
+  return YES;
+}
+
+@end