add helper to create fancy underlines

src/core/SkGlyph.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkGlyph_DEFINED
 #define SkGlyph_DEFINED
 
@@ skipping 16 matching lines @@
     enum {
         kSubBits = 2,
         kSubMask = ((1 << kSubBits) - 1),
         kSubShift = 24, // must be large enough for glyphs and unichars
         kCodeMask = ((1 << kSubShift) - 1),
         // relative offsets for X and Y subpixel bits
         kSubShiftX = kSubBits,
         kSubShiftY = 0
     };
 
- public:
+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
+    };
+
     static const SkFixed kSubpixelRound = SK_FixedHalf >> SkGlyph::kSubBits;
     // A value that can never be generated by MakeID.
     static const uint32_t kImpossibleID = ~0;
     void*       fImage;
     SkPath*     fPath;
+    Intercept*  fIntercept;

[reed1, 2016/02/05 18:56:59]

Hmmm, we already have too much stored in Glyphs, since we typically never have
both a path and an image-ptr. This adds another ptr that will almost always be
null. I wonder if we can find a different way to cache this information (e.g.
separate key, so that the value need not be SkGlyph per-se.)

[caryclark, 2016/02/05 19:43:36]

I can imagine something that looks like

struct GlyphData {
   Type fType;
   union {
      void* fImage;
      SkPath* fPath;
      Intercept* fIntercept;
   };
};

and either the struct or a pointer to it resides in the struct.

Would you like that remedied in this CL or a separate CL?

     SkFixed     fAdvanceX, fAdvanceY;
 
     uint16_t    fWidth, fHeight;
     int16_t     fTop, fLeft;
 
     uint8_t     fMaskFormat;
     int8_t      fRsbDelta, fLsbDelta;  // used by auto-kerning
     int8_t      fForceBW;
 
     void initWithGlyphID(uint32_t glyph_id) {
@@ skipping 73 matching lines @@
         }
     };
 
  private:
     // TODO(herb) remove friend statement after SkGlyphCache cleanup.
     friend class SkGlyphCache;
 
     void initCommon(uint32_t id) {
         fID             = id;
         fImage          = nullptr;
+        fIntercept      = nullptr;
         fPath           = nullptr;
         fMaskFormat     = MASK_FORMAT_UNKNOWN;
         fForceBW        = 0;
     }
 
     static unsigned ID2Code(uint32_t id) {
         return id & kCodeMask;
     }
 
     static unsigned ID2SubX(uint32_t id) {
@@ skipping 33 matching lines @@
   // 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:
 #endif
     uint32_t    fID;
 };
 SK_END_REQUIRE_DENSE
 
 #endif