Support pixel antialising in DirectWrite.

src/ports/SkScalerContext_win_dw.h

Index: src/ports/SkScalerContext_win_dw.h
diff --git a/src/ports/SkScalerContext_win_dw.h b/src/ports/SkScalerContext_win_dw.h
index 98c4910b27f0501d9df0fa7d2e924d371c2bf998..defd4134c5453095756fbe318d5d26b3d0fc51ce 100644
--- a/src/ports/SkScalerContext_win_dw.h
+++ b/src/ports/SkScalerContext_win_dw.h
@@ -15,7 +15,7 @@
 
 #include <dwrite.h>
 #if SK_HAS_DWRITE_2_H
-#include <dwrite_2.h>
+#  include <dwrite_2.h>
 #endif
 
 class SkGlyph;
@@ -76,9 +76,10 @@ private:
     DWRITE_TEXTURE_TYPE fTextureType;
     DWRITE_MEASURING_MODE fMeasuringMode;
 #if SK_HAS_DWRITE_2_H
-    SkTScopedComPtr<IDWriteFactory2> fFactory2;
-    bool fIsColorFont;
+    DWRITE_TEXT_ANTIALIAS_MODE fAntiAliasMode;

[mtklein, 2016/06/16 13:42:17]

Looks like DWRITE_TEXT_ANTIALIAS_MODE (and _CLEARTYPE and _GRAYSCALE) is part of
dwrite_1.h.  Is the grayscale antialiasing really dwrite_2 dependent?

[bungeman-skia, 2016/06/16 14:31:13]

DWRITE_TEXT_ANTIALIAS_MODE is part of dwrite_1.h. Unfortunately it is only used
in dwrite_1.h by IDWriteBitmapRenderTarget1 which is a weird GDI interop thing
(you need an HDC to create one apparently). It wasn't until dwrite_2.h that
there was a CreateGlyphRunAnalysis that takes DWRITE_TEXT_ANTIALIAS_MODE. In
other words, DWRITE_TEXT_ANTIALIAS_MODE isn't really usable until dwrite_2.h.
I'm not including dwrite_1.h here explicitly I suppose, but DirectWrite says
that any later header contains all the earlier ones (it pretty much has to the
way its designed).

+    DWRITE_GRID_FIT_MODE fGridFitMode;
 #endif
+    bool fIsColorFont;
 };
 
 #endif