prototype for kerning api

BUG=
R=bungeman@google.com

Review URL: https://codereview.chromium.org/29363009

git-svn-id: http://skia.googlecode.com/svn/trunk@12018 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 26 insertions, 0 deletions

diff --git a/include/core/SkTypeface.h b/include/core/SkTypeface.h
index eebb1276f7..af76824f47 100644
--- a/include/core/SkTypeface.h
+++ b/include/core/SkTypeface.h
@@ -225,6 +225,29 @@ public:
      */
     int getUnitsPerEm() const;
 
+    /**
+     *  Given a run of glyphs, return the associated horizontal adjustments.
+     *  Adjustments are in "design units", which are integers relative to the
+     *  typeface's units per em (see getUnitsPerEm).
+     *
+     *  Some typefaces are known to never support kerning. Calling this method
+     *  with all zeros (e.g. getKerningPairAdustments(NULL, 0, NULL)) returns
+     *  a boolean indicating if the typeface might support kerning. If it
+     *  returns false, then it will always return false (no kerning) for all
+     *  possible glyph runs. If it returns true, then it *may* return true for
+     *  somne glyph runs.
+     *
+     *  If count is non-zero, then the glyphs parameter must point to at least
+     *  [count] valid glyph IDs, and the adjustments parameter must be
+     *  sized to at least [count - 1] entries. If the method returns true, then
+     *  [count-1] entries in the adjustments array will be set. If the method
+     *  returns false, then no kerning should be applied, and the adjustments
+     *  array will be in an undefined state (possibly some values may have been
+     *  written, but none of them should be interpreted as valid values).
+     */
+    bool getKerningPairAdjustments(const uint16_t glyphs[], int count,
+                                   int32_t adjustments[]) const;
+
     struct LocalizedString {
         SkString fString;
         SkString fLanguage;
@@ -303,6 +326,7 @@ protected:
                         SkAdvancedTypefaceMetrics::PerGlyphInfo perGlyphInfo,
                         const uint32_t* glyphIDs,
                         uint32_t glyphIDsCount) const = 0;
+
     virtual SkStream* onOpenStream(int* ttcIndex) const = 0;
     virtual void onGetFontDescriptor(SkFontDescriptor*, bool* isLocal) const = 0;
 
@@ -311,6 +335,8 @@ protected:
     virtual int onCountGlyphs() const = 0;
 
     virtual int onGetUPEM() const = 0;
+    virtual bool onGetKerningPairAdjustments(const uint16_t glyphs[], int count,
+                                             int32_t adjustments[]) const;
 
     virtual LocalizedStrings* onCreateFamilyNameIterator() const = 0;