Vertically center multi-line RenderTextHarfBuzz that uses SetMinLineHeight().

ui/gfx/render_text_unittest.cc

Index: ui/gfx/render_text_unittest.cc
diff --git a/ui/gfx/render_text_unittest.cc b/ui/gfx/render_text_unittest.cc
index dfd2111875670aa5eab66ab8ce8a42a10630db6c..d262f5f5d790806a4c9ef9fd07d905702f08f243 100644
--- a/ui/gfx/render_text_unittest.cc
+++ b/ui/gfx/render_text_unittest.cc
@@ -116,6 +116,10 @@ class RenderTextTestApi {
     return render_text_->GetAlignmentOffset(line_number);
   }
 
+  int GetDisplayTextBaseline() {
+    return render_text_->GetDisplayTextBaseline();
+  }
+
  private:
   RenderText* render_text_;
 
@@ -4405,6 +4409,100 @@ TEST_P(RenderTextTest, InvalidFont) {
   DrawVisualText();
 }
 
+// Ensures that text is centered vertically and consistently when either the
+// display rectangle height changes, or when the minimum line height changes.
+// The difference between the two is the selection rectangle, which should match
+// the line height.
+TEST_P(RenderTextHarfBuzzTest, BaselineWithLineHeight) {
+  RenderText* render_text = GetRenderText();
+  const int font_height = render_text->font_list().GetHeight();
+  render_text->SetDisplayRect(Rect(500, font_height));
+  render_text->SetText(ASCIIToUTF16("abc"));
+
+  // Select everything so the test can use GetSelectionBoundsUnion().
+  render_text->SelectAll(false);
+
+  const int normal_baseline = test_api()->GetDisplayTextBaseline();
+  ASSERT_EQ(1u, test_api()->lines().size());
+  EXPECT_EQ(font_height, test_api()->lines()[0].size.height());
+
+  // With a matching display height, the baseline calculated using font metrics
+  // and the baseline from the layout engine should agree. This works because
+  // the text string is simple (exotic glyphs may use fonts with different
+  // metrics).
+  EXPECT_EQ(normal_baseline, render_text->GetBaseline());
+  EXPECT_EQ(0, render_text->GetLineOffset(0).y());
+
+  const gfx::Rect normal_selection_bounds = GetSelectionBoundsUnion();
+
+  // Sanity check: selection should start from (0,0).
+  EXPECT_EQ(gfx::Vector2d(), normal_selection_bounds.OffsetFromOrigin());
+
+  constexpr int kDelta = 16;
+
+  // Grow just the display rectangle.
+  render_text->SetDisplayRect(Rect(500, font_height + kDelta));
+
+  // The display text baseline does not move: GetLineOffset() moves it instead.
+  EXPECT_EQ(normal_baseline, test_api()->GetDisplayTextBaseline());
+
+  ASSERT_EQ(1u, test_api()->lines().size());
+  EXPECT_EQ(font_height, test_api()->lines()[0].size.height());
+
+  // Save the baseline calculated using the display rectangle before enabling
+  // multi-line or SetMinLineHeight().
+  const int reported_baseline = render_text->GetBaseline();
+  const int baseline_shift = reported_baseline - normal_baseline;
+
+  // When line height matches font height, this should match the line offset.
+  EXPECT_EQ(baseline_shift, render_text->GetLineOffset(0).y());
+
+  // The actual shift depends on font metrics, and the calculations done in
+  // RenderText::DetermineBaselineCenteringText(). Do a sanity check that the
+  // "centering" part is happening within some tolerance by ensuring the shift
+  // is within a pixel of (kDelta / 2). That is, 7, 8 or 9 pixels (for a delta
+  // of 16). An unusual font in future may need more leeway.
+  constexpr int kFuzz = 1;  // If the next EXPECT fails, try increasing this.
+  EXPECT_LE(abs(baseline_shift - kDelta / 2), kFuzz);
+
+  // Increasing display height (but not line height) should shift the selection
+  // bounds down by |baseline_shift|, but leave a matching size.
+  gfx::Rect current_selection_bounds = GetSelectionBoundsUnion();
+  EXPECT_EQ(baseline_shift, current_selection_bounds.y());
+  EXPECT_EQ(0, current_selection_bounds.x());
+  EXPECT_EQ(normal_selection_bounds.size(), current_selection_bounds.size());
+
+  // Now increase the line height, but remain single-line. Note the line height
+  // now matches the display rect.
+  render_text->SetMinLineHeight(font_height + kDelta);
+  int display_text_baseline = test_api()->GetDisplayTextBaseline();
+  ASSERT_EQ(1u, test_api()->lines().size());
+  EXPECT_EQ(font_height + kDelta, test_api()->lines()[0].size.height());
+
+  // The line offset should go back to zero, but now the display text baseline
+  // should shift down to compensate, and the shift amount should match.
+  EXPECT_EQ(0, render_text->GetLineOffset(0).y());
+  EXPECT_EQ(normal_baseline + baseline_shift, display_text_baseline);
+
+  // Now selection bounds should grow in height, but not shift its origin.
+  current_selection_bounds = GetSelectionBoundsUnion();
+  EXPECT_EQ(font_height + kDelta, current_selection_bounds.height());
+  EXPECT_EQ(normal_selection_bounds.width(), current_selection_bounds.width());
+  EXPECT_EQ(gfx::Vector2d(), current_selection_bounds.OffsetFromOrigin());
+
+  // Flipping the multiline flag should change nothing.
+  render_text->SetMultiline(true);
+  display_text_baseline = test_api()->GetDisplayTextBaseline();
+  ASSERT_EQ(1u, test_api()->lines().size());
+  EXPECT_EQ(font_height + kDelta, test_api()->lines()[0].size.height());
+  EXPECT_EQ(0, render_text->GetLineOffset(0).y());
+  EXPECT_EQ(normal_baseline + baseline_shift, display_text_baseline);
+  current_selection_bounds = GetSelectionBoundsUnion();
+  EXPECT_EQ(font_height + kDelta, current_selection_bounds.height());
+  EXPECT_EQ(normal_selection_bounds.width(), current_selection_bounds.width());
+  EXPECT_EQ(gfx::Vector2d(), current_selection_bounds.OffsetFromOrigin());
+}
+
 // Prefix for test instantiations intentionally left blank since each test
 // fixture class has a single parameterization.
 #if defined(OS_MACOSX)