RenderText: handle center-aligned text in UpdateCachedBoundsAndOffset()

In case display width is less than content width,
UpdateCachedBoundsAndOffset() does not handle center-aligned text
properly when content width is reduced (e.g. by deleting some
characters) or display width is increased.

BUG=none

Review URL: https://codereview.chromium.org/384953003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284897 0039d316-1c4b-4281-b951-d872f2087c98

ui/gfx/render_text.cc

@@ -900,11 +900,12 @@ const Vector2d& RenderText::GetUpdatedDisplayOffset() {
 
 void RenderText::SetDisplayOffset(int horizontal_offset) {
   const int extra_content = GetContentWidth() - display_rect_.width();
+  const int cursor_width = cursor_enabled_ ? 1 : 0;
 
   int min_offset = 0;
   int max_offset = 0;
   if (extra_content > 0) {
-    switch (horizontal_alignment_) {
+    switch (GetCurrentHorizontalAlignment()) {
       case ALIGN_LEFT:
         min_offset = -extra_content;
         break;
@@ -912,8 +913,12 @@ void RenderText::SetDisplayOffset(int horizontal_offset) {
         max_offset = extra_content;
         break;
       case ALIGN_CENTER:
-        min_offset = -extra_content / 2;
-        max_offset = extra_content / 2;
+        // The extra space reserved for cursor at the end of the text is ignored
+        // when centering text. So, to calculate the valid range for offset, we
+        // exclude that extra space, calculate the range, and add it back to the
+        // range (if cursor is enabled).
+        min_offset = -(extra_content - cursor_width + 1) / 2 - cursor_width;
+        max_offset = (extra_content - cursor_width) / 2;
         break;
       default:
         break;
@@ -1400,49 +1405,24 @@ void RenderText::UpdateCachedBoundsAndOffset() {
 
   // TODO(ckocagil): Add support for scrolling multiline text.
 
-  // First, set the valid flag true to calculate the current cursor bounds using
-  // the stale |display_offset_|. Applying |delta_offset| at the end of this
-  // function will set |cursor_bounds_| and |display_offset_| to correct values.
-  cached_bounds_and_offset_valid_ = true;
-  if (cursor_enabled())
-    cursor_bounds_ = GetCursorBounds(selection_model_, insert_mode_);
+  int delta_x = 0;
 
-  // Update |display_offset_| to ensure the current cursor is visible.
-  const int display_width = display_rect_.width();
-  const int content_width = GetContentWidth();
+  if (cursor_enabled()) {
+    // When cursor is enabled, ensure it is visible. For this, set the valid
+    // flag true and calculate the current cursor bounds using the stale
+    // |display_offset_|. Then calculate the change in offset needed to move the
+    // cursor into the visible area.
+    cached_bounds_and_offset_valid_ = true;
+    cursor_bounds_ = GetCursorBounds(selection_model_, insert_mode_);
 
-  int delta_x = 0;
-  if (content_width <= display_width || !cursor_enabled()) {
-    // Don't pan if the text fits in the display width or when the cursor is
-    // disabled.
-    delta_x = -display_offset_.x();
-  } else if (cursor_bounds_.right() > display_rect_.right()) {
-    // TODO(xji): when the character overflow is a RTL character, currently, if
-    // we pan cursor at the rightmost position, the entered RTL character is not
-    // displayed. Should pan cursor to show the last logical characters.
-    //
-    // Pan to show the cursor when it overflows to the right.
-    delta_x = display_rect_.right() - cursor_bounds_.right();
-  } else if (cursor_bounds_.x() < display_rect_.x()) {
-    // TODO(xji): have similar problem as above when overflow character is a
-    // LTR character.
-    //
-    // Pan to show the cursor when it overflows to the left.
-    delta_x = display_rect_.x() - cursor_bounds_.x();
-  } else if (display_offset_.x() != 0) {
-    // Reduce the pan offset to show additional overflow text when the display
-    // width increases.
-    HorizontalAlignment horizontal_alignment = GetCurrentHorizontalAlignment();
-    const int negate_rtl = horizontal_alignment == ALIGN_RIGHT ? -1 : 1;
-    const int offset = negate_rtl * display_offset_.x();
-    if (display_width > (content_width + offset)) {
-      delta_x = negate_rtl * (display_width - (content_width + offset));
-    }
+    // TODO(bidi): Show RTL glyphs at the cursor position for ALIGN_LEFT, etc.
+    if (cursor_bounds_.right() > display_rect_.right())
+      delta_x = display_rect_.right() - cursor_bounds_.right();
+    else if (cursor_bounds_.x() < display_rect_.x())
+      delta_x = display_rect_.x() - cursor_bounds_.x();
   }
 
-  Vector2d delta_offset(delta_x, 0);
-  display_offset_ += delta_offset;
-  cursor_bounds_ += delta_offset;
+  SetDisplayOffset(display_offset_.x() + delta_x);
 }
 
 void RenderText::DrawSelection(Canvas* canvas) {

ui/gfx/render_text_unittest.cc

@@ -1079,6 +1079,42 @@ TEST_F(RenderTextTest, MoveCursorLeftRightWithSelection) {
   render_text->MoveCursor(CHARACTER_BREAK, CURSOR_RIGHT, false);
   EXPECT_EQ(Range(4), render_text->selection());
 }
+
+TEST_F(RenderTextTest, CenteredDisplayOffset) {
+  scoped_ptr<RenderText> render_text(RenderText::CreateInstance());
+  render_text->SetText(ASCIIToUTF16("abcdefghij"));
+  render_text->SetHorizontalAlignment(ALIGN_CENTER);
+
+  const int kEnlargement = 10;
+  const int content_width = render_text->GetContentWidth();
+  Rect display_rect(0, 0, content_width / 2,
+                    render_text->font_list().GetHeight());
+  render_text->SetDisplayRect(display_rect);
+
+  // Move the cursor to the beginning of the text and, by checking the cursor
+  // bounds, make sure no empty space is to the left of the text.
+  render_text->SetCursorPosition(0);
+  EXPECT_EQ(display_rect.x(), render_text->GetUpdatedCursorBounds().x());
+
+  // Widen the display rect and, by checking the cursor bounds, make sure no
+  // empty space is introduced to the left of the text.
+  display_rect.Inset(0, 0, -kEnlargement, 0);
+  render_text->SetDisplayRect(display_rect);
+  EXPECT_EQ(display_rect.x(), render_text->GetUpdatedCursorBounds().x());
+
+  // Move the cursor to the end of the text and, by checking the cursor bounds,
+  // make sure no empty space is to the right of the text.
+  render_text->SetCursorPosition(render_text->text().length());
+  EXPECT_EQ(display_rect.right(),
+            render_text->GetUpdatedCursorBounds().right());
+
+  // Widen the display rect and, by checking the cursor bounds, make sure no
+  // empty space is introduced to the right of the text.
+  display_rect.Inset(0, 0, -kEnlargement, 0);
+  render_text->SetDisplayRect(display_rect);
+  EXPECT_EQ(display_rect.right(),
+            render_text->GetUpdatedCursorBounds().right());
+}
 #endif  // !defined(OS_MACOSX)
 
 // TODO(xji): Make these work on Windows.
@@ -1559,11 +1595,11 @@ TEST_F(RenderTextTest, SetDisplayOffset) {
     { ALIGN_RIGHT, kEnlargement / 2, kEnlargement / 2 },
     { ALIGN_RIGHT, 2 * kEnlargement, kEnlargement },
     // When text is center-aligned, display offset can be in range
-    // [-kEnlargement / 2, kEnlargement / 2].
-    { ALIGN_CENTER, -kEnlargement, -kEnlargement / 2 },
+    // [-kEnlargement / 2 - 1, (kEnlargement - 1) / 2].
+    { ALIGN_CENTER, -kEnlargement, -kEnlargement / 2 - 1 },
     { ALIGN_CENTER, -kEnlargement / 4, -kEnlargement / 4 },
     { ALIGN_CENTER, kEnlargement / 4, kEnlargement / 4 },
-    { ALIGN_CENTER, kEnlargement, kEnlargement / 2 },
+    { ALIGN_CENTER, kEnlargement, (kEnlargement - 1) / 2 },
   };
 
   for (size_t i = 0; i < ARRAYSIZE_UNSAFE(large_content_cases); i++) {