Lift out ExpandRangeToGraphemeBoundary

The lifted function is similar to the ExpandRangeToWordBoundary(...).
It allows to get the enclosing range at grapheme boundaries.

R=pkasting@chromium.org

Bug: 1025561
Change-Id: I4f439b81ac0c1c7e540f67b98c9e3e7f9757b36b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982714
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727676}

ui/gfx/render_text.cc

@@ -1035,7 +1035,7 @@ bool RenderText::IsValidLogicalIndex(size_t index) const {
        IsValidCodePointIndex(text(), index));
 }
 
-bool RenderText::IsValidCursorIndex(size_t index) {
+bool RenderText::IsValidCursorIndex(size_t index) const {
   return index == 0 || index == text().length() ||
          (IsValidLogicalIndex(index) && IsGraphemeBoundary(index));
 }
@@ -1266,6 +1266,19 @@ base::string16 RenderText::GetTextFromRange(const Range& range) const {
   return base::string16();
 }
 
+Range RenderText::ExpandRangeToGraphemeBoundary(const Range& range) const {
+  const auto snap_to_grapheme = [this](auto index, auto direction) {
+    return IsValidCursorIndex(index)
+               ? index
+               : IndexOfAdjacentGrapheme(index, direction);
+  };
+
+  const size_t min_index = snap_to_grapheme(range.GetMin(), CURSOR_BACKWARD);
+  const size_t max_index = snap_to_grapheme(range.GetMax(), CURSOR_FORWARD);
+  return range.is_reversed() ? Range(max_index, min_index)
+                             : Range(min_index, max_index);
+}
+
 bool RenderText::IsNewlineSegment(const internal::LineSegment& segment) const {
   return IsNewlineSegment(text_, segment);
 }

ui/gfx/render_text.h

@@ -488,7 +488,7 @@ class GFX_EXPORT RenderText {
 
   // Returns true if the position is a valid logical index into text(), and is
   // also a valid grapheme boundary, which may be used as a cursor position.
-  bool IsValidCursorIndex(size_t index);
+  bool IsValidCursorIndex(size_t index) const;
 
   // Get the visual bounds of a cursor at |caret|. These bounds typically
   // represent a vertical line if |insert_mode| is true. Pass false for
@@ -586,6 +586,10 @@ class GFX_EXPORT RenderText {
   // line if the |caret| exceeds the text length.
   virtual size_t GetLineContainingCaret(const SelectionModel& caret) = 0;
 
+  // Expands |range| to its nearest grapheme boundaries and returns the
+  // resulting range. Maintains directionality of |range|.
+  Range ExpandRangeToGraphemeBoundary(const Range& range) const;
+
  protected:
   RenderText();
 

ui/gfx/render_text_harfbuzz.cc

@@ -1396,16 +1396,9 @@ std::vector<Rect> RenderTextHarfBuzz::GetSubstringBounds(const Range& range) {
   EnsureLayout();
   DCHECK(!update_display_run_list_);
   DCHECK(Range(0, text().length()).Contains(range));
-  const size_t start =
-      IsValidCursorIndex(range.GetMin())
-          ? range.GetMin()
-          : IndexOfAdjacentGrapheme(range.GetMin(), CURSOR_BACKWARD);
-  const size_t end =
-      IsValidCursorIndex(range.GetMax())
-          ? range.GetMax()
-          : IndexOfAdjacentGrapheme(range.GetMax(), CURSOR_FORWARD);
-  const Range display_range(TextIndexToDisplayIndex(start),
-                            TextIndexToDisplayIndex(end));
+  const Range grapheme_range = ExpandRangeToGraphemeBoundary(range);
+  const Range display_range(TextIndexToDisplayIndex(grapheme_range.start()),
+                            TextIndexToDisplayIndex(grapheme_range.end()));
   DCHECK(Range(0, GetDisplayText().length()).Contains(display_range));
 
   std::vector<Rect> rects;
@@ -1698,17 +1691,10 @@ void RenderTextHarfBuzz::DrawVisualText(internal::SkiaTextRenderer* renderer,
   // Apply the selected text color to the [un-reversed] selection range.
   BreakList<SkColor> colors = layout_colors();
   if (!selection.is_empty()) {
-    const size_t grapheme_start =
-        IsGraphemeBoundary(selection.GetMin())
-            ? selection.GetMin()
-            : IndexOfAdjacentGrapheme(selection.GetMin(), CURSOR_BACKWARD);
-    const size_t grapheme_end =
-        IsGraphemeBoundary(selection.GetMax())
-            ? selection.GetMax()
-            : IndexOfAdjacentGrapheme(selection.GetMax(), CURSOR_FORWARD);
+    const Range grapheme_range = ExpandRangeToGraphemeBoundary(selection);
     colors.ApplyValue(selection_color(),
-                      Range(TextIndexToDisplayIndex(grapheme_start),
-                            TextIndexToDisplayIndex(grapheme_end)));
+                      Range(TextIndexToDisplayIndex(grapheme_range.GetMin()),
+                            TextIndexToDisplayIndex(grapheme_range.GetMax())));
   }
 
   internal::TextRunList* run_list = GetRunList();