Generate Signed Distance Field directly from vector path

src/gpu/GrDistanceFieldGenFromVector.h

+/*

[jvanverth1, 2017/01/04 21:12:27]

Is there a reason this file is in src/gpu and not in src/core as
SkDistanceFieldGenFromVector.h?

[Joel.Liang, 2017/01/06 05:28:09]

It's because we used the GrPathUtils::convertCubicToQuads() function to convert
Cubic path.
And I think Signed Distance Field should only available in GPU related build.

Please see here for more detail:
https://codereview.chromium.org/1643143002/#msg19

+ * Copyright 2016 ARM Ltd.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrDistanceFieldGenFromVector_DEFINED
+#define GrDistanceFieldGenFromVector_DEFINED
+
+#include "SkDistanceFieldGen.h"

[jvanverth1, 2017/01/04 21:12:27]

This include could be in GrDistanceFieldGenFromVector.cpp instead.

[Joel.Liang, 2017/01/06 05:28:09]

Done.

+#include "SkPath.h"
+#include "SkMatrix.h"

[jvanverth1, 2017/01/04 21:12:27]

This could be replaced by 

class Matrix; 

and put the include in GrDistanceFieldGenFromVector.h.

[Joel.Liang, 2017/01/06 05:28:09]

Done.

+

[jvanverth1, 2017/01/04 21:12:27]

Add #define SK_USE_LEGACY_DISTANCE_FIELDS here?

[Joel.Liang, 2017/01/06 05:28:09]

Done.

And I have added an #ifndef directive to surround it to avoid redefinition with
the SkUserConfig.h file in Chromium.

+/** Given a vector path, generate the associated distance field.
+
+ *  @param distanceField     The distance field to be generated. Should already be allocated
+ *                           by the client with the padding defined in "SkDistanceFieldGen.h".
+ *  @param path              The path we're using to generate the distance field.
+ *  @param matrix            Transformation matrix for path.
+ *  @param width             Width of the distance field.
+ *  @param height            Height of the distance field.
+ *  @param rowBytes          Size of each row in the distance field, in bytes.
+ */
+bool GrGenerateDistanceFieldFromPath(unsigned char* distanceField,
+                                     const SkPath& path, const SkMatrix& viewMatrix,
+                                     int width, int height, size_t rowBytes);
+
+inline bool IsDistanceFieldSupportedFillType(SkPath::FillType fFillType)
+{
+        return (SkPath::kEvenOdd_FillType == fFillType ||
+            SkPath::kInverseEvenOdd_FillType == fFillType);
+}
+
+#endif