add helper to create fancy underlines

src/core/SkGlyph.h

Index: src/core/SkGlyph.h
diff --git a/src/core/SkGlyph.h b/src/core/SkGlyph.h
index 92f974bc2cf456f8ed367c5f8d0c676baa8a2f26..87ce6f903e7a1594f4df4e85621c8afd3d738e56 100644
--- a/src/core/SkGlyph.h
+++ b/src/core/SkGlyph.h
@@ -34,7 +34,19 @@ class SkGlyph {
         kSubShiftY = 0
     };
 
- public:
+    // Support horizontal and vertical skipping strike-through / underlines.
+    // The caller walks the linked list looking for a match. For a horizontal underline,
+    // the fBounds contains the top and bottom of the underline. The fInterval pair contains the
+    // beginning and end of of the intersection of the bounds and the glyph's path.
+    // If interval[0] >= interval[1], no intesection was found.
+    struct Intercept {
+        Intercept* fNext;
+        SkScalar fBounds[2];    // for horz underlines, the boundaries in Y
+        SkScalar fInterval[2];  // the outside intersections of the axis and the glyph
+    };
+
+    Intercept*  fIntercept;

[f(malita), 2016/02/08 14:20:27]

Caching this is nice, but may be overkill at this stage.  Since we don't know
how widely this feature is going to be used in Blink, is this something we can
defer for later (if needed)?

[caryclark, 2016/02/09 19:10:57]

If the same glyphs are underlined widely by the caller, the cache could make an
enormous performance difference. To mitigate the concerns about increasing the
size of the cache, I restructured the CL so that the same slot contains the
cached path and the cached underline.

+public:
     static const SkFixed kSubpixelRound = SK_FixedHalf >> SkGlyph::kSubBits;
     // A value that can never be generated by MakeID.
     static const uint32_t kImpossibleID = ~0;
@@ -133,6 +145,7 @@ class SkGlyph {
     void initCommon(uint32_t id) {
         fID             = id;
         fImage          = nullptr;
+        fIntercept      = nullptr;
         fPath           = nullptr;
         fMaskFormat     = MASK_FORMAT_UNKNOWN;
         fForceBW        = 0;
@@ -176,7 +189,7 @@ class SkGlyph {
         return ID;
     }
 
-  // FIXME - This is needed because the Android frame work directly
+    // FIXME - This is needed because the Android frame work directly
   // accesses fID. Remove when fID accesses are cleaned up.
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
   public: