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/*
* 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 <new>
enum class SkFilterMode {
kNearest, // single sample point (nearest neighbor)
kLinear, // interporate between 2x2 sample points (bilinear interpolation)
kLast = kLinear,
};
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,
};
/*
* 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 bool useCubic = false;
const SkCubicResampler cubic = {0, 0};
const SkFilterMode filter = SkFilterMode::kNearest;
const SkMipmapMode mipmap = SkMipmapMode::kNone;
SkSamplingOptions() = default;
SkSamplingOptions(const SkSamplingOptions&) = default;
SkSamplingOptions& operator=(const SkSamplingOptions& that) {
this->~SkSamplingOptions(); // A pedantic no-op.
new (this) SkSamplingOptions(that);
return *this;
}
SkSamplingOptions(SkFilterMode fm, SkMipmapMode mm)
: useCubic(false)
, filter(fm)
, mipmap(mm) {}
explicit SkSamplingOptions(SkFilterMode fm)
: useCubic(false)
, filter(fm)
, mipmap(SkMipmapMode::kNone) {}
explicit SkSamplingOptions(const SkCubicResampler& c)
: useCubic(true)
, cubic(c) {}
bool operator==(const SkSamplingOptions& other) const {
return 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); }
};
#endif
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