1 files changed, 105 insertions, 0 deletions
diff --git a/gfx/skia/skia/include/core/SkSamplingOptions.h b/gfx/skia/skia/include/core/SkSamplingOptions.h
new file mode 100644
index 0000000000..24b6d51659
--- /dev/null
+++ b/gfx/skia/skia/include/core/SkSamplingOptions.h
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2020 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageSampling_DEFINED
+#define SkImageSampling_DEFINED
+
+#include "include/core/SkTypes.h"
+
+#include <algorithm>
+#include <new>
+
+enum class SkFilterMode {
+    kNearest,   // single sample point (nearest neighbor)
+    kLinear,    // interporate between 2x2 sample points (bilinear interpolation)
+
+    kLast = kLinear,
+};
+static constexpr int kSkFilterModeCount = static_cast<int>(SkFilterMode::kLast) + 1;
+
+enum class SkMipmapMode {
+    kNone,      // ignore mipmap levels, sample from the "base"
+    kNearest,   // sample from the nearest level
+    kLinear,    // interpolate between the two nearest levels
+
+    kLast = kLinear,
+};
+static constexpr int kSkMipmapModeCount = static_cast<int>(SkMipmapMode::kLast) + 1;
+
+/*
+ *  Specify B and C (each between 0...1) to create a shader that applies the corresponding
+ *  cubic reconstruction filter to the image.
+ *
+ *  Example values:
+ *      B = 1/3, C = 1/3        "Mitchell" filter
+ *      B = 0,   C = 1/2        "Catmull-Rom" filter
+ *
+ *  See "Reconstruction Filters in Computer Graphics"
+ *          Don P. Mitchell
+ *          Arun N. Netravali
+ *          1988
+ *  https://www.cs.utexas.edu/~fussell/courses/cs384g-fall2013/lectures/mitchell/Mitchell.pdf
+ *
+ *  Desmos worksheet https://www.desmos.com/calculator/aghdpicrvr
+ *  Nice overview https://entropymine.com/imageworsener/bicubic/
+ */
+struct SkCubicResampler {
+    float B, C;
+
+    // Historic default for kHigh_SkFilterQuality
+    static constexpr SkCubicResampler Mitchell() { return {1/3.0f, 1/3.0f}; }
+    static constexpr SkCubicResampler CatmullRom() { return {0.0f, 1/2.0f}; }
+};
+
+struct SK_API SkSamplingOptions {
+    const int              maxAniso = 0;
+    const bool             useCubic = false;
+    const SkCubicResampler cubic    = {0, 0};
+    const SkFilterMode     filter   = SkFilterMode::kNearest;
+    const SkMipmapMode     mipmap   = SkMipmapMode::kNone;
+
+    constexpr SkSamplingOptions() = default;
+    SkSamplingOptions(const SkSamplingOptions&) = default;
+    SkSamplingOptions& operator=(const SkSamplingOptions& that) {
+        this->~SkSamplingOptions();   // A pedantic no-op.
+        new (this) SkSamplingOptions(that);
+        return *this;
+    }
+
+    constexpr SkSamplingOptions(SkFilterMode fm, SkMipmapMode mm)
+        : filter(fm)
+        , mipmap(mm) {}
+
+    explicit constexpr SkSamplingOptions(SkFilterMode fm)
+        : filter(fm)
+        , mipmap(SkMipmapMode::kNone) {}
+
+    explicit constexpr SkSamplingOptions(const SkCubicResampler& c)
+        : useCubic(true)
+        , cubic(c) {}
+
+    static constexpr SkSamplingOptions Aniso(int maxAniso) {
+        return SkSamplingOptions{std::max(maxAniso, 1)};
+    }
+
+    bool operator==(const SkSamplingOptions& other) const {
+        return maxAniso == other.maxAniso
+            && useCubic == other.useCubic
+            && cubic.B  == other.cubic.B
+            && cubic.C  == other.cubic.C
+            && filter   == other.filter
+            && mipmap   == other.mipmap;
+    }
+    bool operator!=(const SkSamplingOptions& other) const { return !(*this == other); }
+
+    bool isAniso() const { return maxAniso != 0; }
+
+private:
+    constexpr SkSamplingOptions(int maxAniso) : maxAniso(maxAniso) {}
+};
+
+#endif