Initial linear gradient 4f impl

src/effects/gradients/Sk4fLinearGradient.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 Sk4fLinearGradient_DEFINED
+#define Sk4fLinearGradient_DEFINED
+
+#include "Sk4fGradientBase.h"
+#include "SkLinearGradient.h"
+
+class SkLinearGradient::
+LinearGradient4fContext : public GradientShaderBase4fContext {
+public:
+    LinearGradient4fContext(const SkLinearGradient&, const ContextRec&);
+
+    void shadeSpan(int x, int y, SkPMColor dst[], int count) override;
+    void shadeSpan4f(int x, int y, SkPM4f dst[], int count) override;
+
+private:
+    using INHERITED = GradientShaderBase4fContext;
+
+    template<typename DstType, TileMode>
+    class LinearIntervalProcessor;
+
+    template <typename DstType, bool premul>
+    void shadePremulSpan(int x, int y, DstType[], int count) const;
+
+    template <typename DstType, bool premul, SkShader::TileMode tileMode>
+    void shadePremulTileSpan(int x, int y, DstType[], int count) const;
+
+    template <typename DstType, bool premul, SkShader::TileMode tileMode>
+    void shadeSpanInternal(int x, int y, DstType[], int count) const;
+};
+
+#endif // Sk4fLinearGradient_DEFINED