add helper to create fancy underlines

include/core/SkPaint.h

Index: include/core/SkPaint.h
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index 51e8848a00b6f3ad07d6ed72a513941377cb5247..5c827e8c1543b5c91e4356907b910de35e578915 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -883,15 +883,59 @@ public:
                       SkRect bounds[] = NULL) const;
 
     /** Return the path (outline) for the specified text.
-        Note: just like SkCanvas::drawText, this will respect the Align setting
-              in the paint.
-    */
+     *  Note: just like SkCanvas::drawText, this will respect the Align setting
+     *        in the paint.
+     *
+     *  @param text         the text
+     *  @param length       number of bytes of text
+     *  @param x            The x-coordinate of the origin of the text.
+     *  @param y            The y-coordinate of the origin of the text.
+     *  @param path         The outline of the text.
+     */
     void getTextPath(const void* text, size_t length, SkScalar x, SkScalar y,
                      SkPath* path) const;
 
+    /** Return the path (outline) for the specified text.
+     *  Note: just like SkCanvas::drawText, this will respect the Align setting
+     *        in the paint.
+     *
+     *  @param text         the text
+     *  @param length       number of bytes of text
+     *  @param pos          array of positions, used to position each character
+     *  @param path         The outline of the text.
+     */
     void getPosTextPath(const void* text, size_t length,
                         const SkPoint pos[], SkPath* path) const;
 
+    /** Return the number of intervals that intersect the intercept along the axis of the advance.
+     *  This permits constructing an underline that skips the descenders. 
+     *
+     *  @param text         the text
+     *  @param length       number of bytes of text
+     *  @param x            The x-coordinate of the origin of the text.
+     *  @param y            The y-coordinate of the origin of the text.
+     *  @param bounds       The lower and upper line parallel to the advance.
+     *  @param array        If not null, the found intersections.
+     *
+     *  @return             The number of intersections.
+     */
+    int getTextIntercepts(const void* text, size_t length, SkScalar x, SkScalar y,

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

If there is any extra burden, we can decide to not offer this variant, and just
force clients to construct the positions and call getPosTextIntercepts.

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

The burden is very slight; nearly all of the code is shared with the pos
variant.
If you prefer, I'll remove it anyway.

+                          SkScalar bounds[2], SkScalar* array) const;
+
+    /** Return the number of intervals that intersect the intercept along the axis of the advance.
+     *  This permits constructing an underline that skips the descenders. 
+     *
+     *  @param text         the text
+     *  @param length       number of bytes of text
+     *  @param pos          array of positions, used to position each character
+     *  @param bounds       The lower and upper line parallel to the advance.
+     *  @param array        If not null, the glyph bounds contained by the advance parallel lines.
+     *
+     *  @return             The number of glyph bounds.
+     */
+    int getPosTextIntercepts(const void* text, size_t length, const SkPoint pos[],
+                             SkScalar bounds[2], SkScalar* array) const;

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

SkScalar intervals[] ?

Is an upper-bound on the size of this array 2 * number of glyphs? Is that the
exact size?

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

const SkScalar bounds[2] ?

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

If the string has no descenders at all, the size returned is zero. 
In the current implementation, the upper bounds is 2x # of glyphs. If we choose
that returning the interior of a glyph is also important, that would of course
increase.

Make bounds const (done)

+
     /**
      *  Return a rectangle that represents the union of the bounds of all
      *  of the glyphs, but each one positioned at (0,0). This may be conservatively large, and
@@ -1089,7 +1133,7 @@ private:
     friend class GrTextUtils;
     friend class GrGLPathRendering;
     friend class SkScalerContext;
-    friend class SkTextToPathIter;
+    friend class SkTextBaseIter;
     friend class SkCanonicalizePaint;
 };