linux: Make RenderTextPango avoid clipping underlines.

Adjust underline positions so the lines won't get clipped. I
think that the inaccuracy may be occurring due to our
conversion from PangoFontDescriptions (usually containing a
point-based size) to a rounded pixel-based size and then
back to a PangoFontDescription. Luckily, RenderTextPango
will be replaced by RenderTextHarfBuzz soon.

Also delete some dead code in PlatformFontPango for
computing underline metrics.

BUG=393117
TEST=manual: checked that the "Import bookmarks now..."
     underline is visible after setting my UI font to
     "Ubuntu 11"

Review URL: https://codereview.chromium.org/509093004

Cr-Commit-Position: refs/heads/master@{#292537}

ui/gfx/platform_font_pango.cc

@@ -130,16 +130,6 @@ PlatformFontPango::PlatformFontPango(const std::string& font_name,
                   query.style, gfx::GetFontRenderParams(query, NULL));
 }
 
-double PlatformFontPango::underline_position() const {
-  const_cast<PlatformFontPango*>(this)->InitPangoMetrics();
-  return underline_position_pixels_;
-}
-
-double PlatformFontPango::underline_thickness() const {
-  const_cast<PlatformFontPango*>(this)->InitPangoMetrics();
-  return underline_thickness_pixels_;
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 // PlatformFontPango, PlatformFont implementation:
 
@@ -283,8 +273,6 @@ void PlatformFontPango::InitFromDetails(
 
   pango_metrics_inited_ = false;
   average_width_pixels_ = 0.0f;
-  underline_position_pixels_ = 0.0f;
-  underline_thickness_pixels_ = 0.0f;
 }
 
 void PlatformFontPango::InitFromPlatformFont(const PlatformFontPango* other) {
@@ -298,8 +286,6 @@ void PlatformFontPango::InitFromPlatformFont(const PlatformFontPango* other) {
   cap_height_pixels_ = other->cap_height_pixels_;
   pango_metrics_inited_ = other->pango_metrics_inited_;
   average_width_pixels_ = other->average_width_pixels_;
-  underline_position_pixels_ = other->underline_position_pixels_;
-  underline_thickness_pixels_ = other->underline_thickness_pixels_;
 }
 
 void PlatformFontPango::PaintSetup(SkPaint* paint) const {
@@ -318,19 +304,6 @@ void PlatformFontPango::InitPangoMetrics() {
     ScopedPangoFontDescription pango_desc(GetNativeFont());
     PangoFontMetrics* pango_metrics = GetPangoFontMetrics(pango_desc.get());
 
-    underline_position_pixels_ =
-        pango_font_metrics_get_underline_position(pango_metrics) /
-        PANGO_SCALE;
-
-    // TODO(davemoore): Come up with a better solution.
-    // This is a hack, but without doing this the underlines
-    // we get end up fuzzy. So we align to the midpoint of a pixel.
-    underline_position_pixels_ /= 2;
-
-    underline_thickness_pixels_ =
-        pango_font_metrics_get_underline_thickness(pango_metrics) /
-        PANGO_SCALE;
-
     // First get the Pango-based width (converting from Pango units to pixels).
     const double pango_width_pixels =
         pango_font_metrics_get_approximate_char_width(pango_metrics) /

ui/gfx/platform_font_pango.h

@@ -40,13 +40,6 @@ class GFX_EXPORT PlatformFontPango : public PlatformFont {
   static void SetDefaultFontDescription(const std::string& font_description);
 #endif
 
-  // Position as an offset from the height of the drawn text, used to draw
-  // an underline. This is a negative number, so the underline would be
-  // drawn at y + height + underline_position.
-  double underline_position() const;
-  // The thickness to draw the underline.
-  double underline_thickness() const;
-
   // Overridden from PlatformFont:
   virtual Font DeriveFont(int size_delta, int style) const OVERRIDE;
   virtual int GetHeight() const OVERRIDE;
@@ -82,7 +75,7 @@ class GFX_EXPORT PlatformFontPango : public PlatformFont {
   // Initializes this object as a copy of another PlatformFontPango.
   void InitFromPlatformFont(const PlatformFontPango* other);
 
-  // Potentially slow call to get pango metrics (average width, underline info).
+  // Potentially slow call to get pango metrics (average width).
   void InitPangoMetrics();
 
   // Setup a Skia context to use the current typeface.
@@ -114,8 +107,6 @@ class GFX_EXPORT PlatformFontPango : public PlatformFont {
   // to compute them.
   bool pango_metrics_inited_;
   double average_width_pixels_;
-  double underline_position_pixels_;
-  double underline_thickness_pixels_;
 
   // The default font, used for the default constructor.
   static Font* default_font_;

ui/gfx/render_text_pango.cc

@@ -55,11 +55,20 @@ void SetPangoUnderlineMetrics(PangoFontDescription *desc,
   // Pango returns the position "above the baseline". Change its sign to convert
   // it to a vertical offset from the baseline.
   int position = -pango_font_metrics_get_underline_position(metrics);
-  pango_quantize_line_geometry(&thickness, &position);
+
   // Note: pango_quantize_line_geometry() guarantees pixel boundaries, so
   //       PANGO_PIXELS() is safe to use.
-  renderer->SetUnderlineMetrics(PANGO_PIXELS(thickness),
-                                PANGO_PIXELS(position));
+  pango_quantize_line_geometry(&thickness, &position);
+  int thickness_pixels = PANGO_PIXELS(thickness);
+  int position_pixels = PANGO_PIXELS(position);
+
+  // Ugly hack: make sure that underlines don't get clipped. See
+  // http://crbug.com/393117.
+  int descent_pixels = PANGO_PIXELS(pango_font_metrics_get_descent(metrics));
+  position_pixels = std::min(position_pixels,
+                             descent_pixels - thickness_pixels);
+
+  renderer->SetUnderlineMetrics(thickness_pixels, position_pixels);
 }
 
 }  // namespace