Adjust visual overflow rect for rounded/shifted ascent/descent

third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp

Index: third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp b/third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp
index ba858b4b7453f5a7dd24d171424b035ca9e80fbc..beb0a4b793c2fc33c418bb1a119dc7e91f1602ce 100644
--- a/third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp
+++ b/third_party/WebKit/Source/platform/fonts/SimpleFontData.cpp
@@ -62,10 +62,12 @@ SimpleFontData::SimpleFontData(const FontPlatformData& platform_data,
     : max_char_width_(-1),
       avg_char_width_(-1),
       platform_data_(platform_data),
-      is_text_orientation_fallback_(is_text_orientation_fallback),
       vertical_data_(nullptr),
+      custom_font_data_(std::move(custom_data)),
+      is_text_orientation_fallback_(is_text_orientation_fallback),
       has_vertical_glyphs_(false),
-      custom_font_data_(std::move(custom_data)) {
+      visual_overflow_inflation_for_ascent_(0),
+      visual_overflow_inflation_for_descent_(0) {
   PlatformInit(subpixel_ascent_descent);
   PlatformGlyphInit();
   if (platform_data.IsVerticalAnyUpright() && !is_text_orientation_fallback) {
@@ -78,9 +80,11 @@ SimpleFontData::SimpleFontData(const FontPlatformData& platform_data,
 SimpleFontData::SimpleFontData(const FontPlatformData& platform_data,
                                PassRefPtr<OpenTypeVerticalData> vertical_data)
     : platform_data_(platform_data),
-      is_text_orientation_fallback_(false),
       vertical_data_(vertical_data),
-      has_vertical_glyphs_(false) {}
+      is_text_orientation_fallback_(false),
+      has_vertical_glyphs_(false),
+      visual_overflow_inflation_for_ascent_(0),
+      visual_overflow_inflation_for_descent_(0) {}
 
 void SimpleFontData::PlatformInit(bool subpixel_ascent_descent) {
   if (!platform_data_.size()) {
@@ -134,30 +138,37 @@ void SimpleFontData::PlatformInit(bool subpixel_ascent_descent) {
   if (is_vdmx_valid) {
     ascent = vdmx_ascent;
     descent = -vdmx_descent;
-  } else {
+  } else if (subpixel_ascent_descent &&
+             (-metrics.fAscent < 3 ||
+              -metrics.fAscent + metrics.fDescent < 2)) {
     // For tiny fonts, the rounding of fAscent and fDescent results in equal
     // baseline for different types of text baselines (crbug.com/338908).
     // Please see CanvasRenderingContext2D::getFontBaseline for the heuristic.
-    if (subpixel_ascent_descent &&
-        (-metrics.fAscent < 3 || -metrics.fAscent + metrics.fDescent < 2)) {
-      ascent = -metrics.fAscent;
-      descent = metrics.fDescent;
-    } else {
-      ascent = SkScalarRoundToScalar(-metrics.fAscent);
-      descent = SkScalarRoundToScalar(metrics.fDescent);
-    }
+    ascent = -metrics.fAscent;
+    descent = metrics.fDescent;
+  } else {
+    ascent = SkScalarRoundToScalar(-metrics.fAscent);
+    descent = SkScalarRoundToScalar(metrics.fDescent);
+
+    if (ascent < -metrics.fAscent)
+      visual_overflow_inflation_for_ascent_ = 1;
+    if (descent < metrics.fDescent) {
+      visual_overflow_inflation_for_descent_ = 1;
 #if OS(LINUX) || OS(ANDROID)
-    // When subpixel positioning is enabled, if the descent is rounded down, the
-    // descent part of the glyph may be truncated when displayed in a 'overflow:
-    // hidden' container.  To avoid that, borrow 1 unit from the ascent when
-    // possible.
-    // FIXME: This can be removed if sub-pixel ascent/descent is supported.
-    if (PlatformData().GetFontRenderStyle().use_subpixel_positioning &&
-        descent < SkScalarToFloat(metrics.fDescent) && ascent >= 1) {
-      ++descent;
-      --ascent;
-    }
+      // When subpixel positioning is enabled, if the descent is rounded down,
+      // the descent part of the glyph may be truncated when displayed in a
+      // 'overflow: hidden' container.  To avoid that, borrow 1 unit from the
+      // ascent when possible.
+      if (PlatformData().GetFontRenderStyle().use_subpixel_positioning &&
+          ascent >= 1) {
+        ++descent;
+        --ascent;
+        // We should inflate overflow 1 more pixel for ascent instead.
+        visual_overflow_inflation_for_descent_ = 0;
+        ++visual_overflow_inflation_for_ascent_;
+      }
 #endif
+    }
   }
 
 #if OS(MACOSX)