Refactoring of CPU NormalMap handling out into its own class

src/core/SkNormalSource.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkNormalSource_DEFINED
+#define SkNormalSource_DEFINED
+
+#include "SkFlattenable.h"
+
+/** Abstract class that generates or reads in normals for use by SkLightingShader. Not to be
+    used as part of the API yet. Used internally by SkLightingShader.
+*/
+class SK_API SkNormalSource : public SkFlattenable {
+public:
+    virtual ~SkNormalSource() override;
+
+#if SK_SUPPORT_GPU
+    /** Returns a fragment processor that takes no input and outputs a normal (already rotated)
+        as its output color. To be used as a child fragment processor.
+    */
+    virtual sk_sp<GrFragmentProcessor> asFragmentProcessor(
+            GrContext* context,
+            const SkMatrix& viewM,
+            const SkMatrix* localMatrix,
+            SkFilterQuality filterQuality,
+            SkSourceGammaTreatment gammaTreatment) const = 0;
+#endif
+
+    class Provider {
+    public:
+        virtual ~Provider() {};
+
+        /** Called for each span of the object being drawn on the CPU. Your subclass should set
+            the appropriate normals that correspond to the specified device coordinates.
+        */
+        virtual void fillScanLine(int x, int y, SkPoint3 output[], int count) const = 0;
+    };
+
+    /** Returns an instance of 'Provider' that provides normals for the CPU pipeline. The
+        necessary data will be initialized in place at 'storage'.
+    */
+    virtual Provider* asProvider(const SkShader::ContextRec&, void* storage) const = 0;
+
+    /** Amount of memory needed to store a provider object and its dependencies.
+     */
+    virtual size_t providerSize(const SkShader::ContextRec&) const = 0;
+
+    /** Returns a normal source that provides normals sourced from the the normal map argument.
+        Not to be used as part of the API yet. Used internally by SkLightingShader.
+
+        @param  map              a shader that outputs the normal map
+        @param  normRotation     rotation applied to the normal map's normals, in the
+                                 [cos a, sin a] form.
+
+        nullptr will be returned if 'map' is null
+
+        The normal map is currently assumed to be an 8888 image where the normal at a texel
+        is retrieved by:
+            N.x = R-127;
+            N.y = G-127;
+            N.z = B-127;
+            N.normalize();
+        The +Z axis is thus encoded in RGB as (127, 127, 255) while the -Z axis is
+        (127, 127, 0).
+    */
+    static sk_sp<SkNormalSource> MakeFromNormalMap(sk_sp<SkShader> map,
+                                                   const SkVector& normRotation);
+
+    SK_DEFINE_FLATTENABLE_TYPE(SkNormalSource)
+    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
+};
+
+#endif