1 | /* |
2 | * Copyright 2020 Google Inc. |
3 | * |
4 | * Use of this source code is governed by a BSD-style license that can be |
5 | * found in the LICENSE file. |
6 | */ |
7 | |
8 | #ifndef SkImageSampling_DEFINED |
9 | #define SkImageSampling_DEFINED |
10 | |
11 | #include "include/core/SkTypes.h" |
12 | |
13 | #include <algorithm> |
14 | #include <new> |
15 | |
16 | enum class SkFilterMode { |
17 | kNearest, // single sample point (nearest neighbor) |
18 | kLinear, // interporate between 2x2 sample points (bilinear interpolation) |
19 | |
20 | kLast = kLinear, |
21 | }; |
22 | static constexpr int kSkFilterModeCount = static_cast<int>(SkFilterMode::kLast) + 1; |
23 | |
24 | enum class SkMipmapMode { |
25 | kNone, // ignore mipmap levels, sample from the "base" |
26 | kNearest, // sample from the nearest level |
27 | kLinear, // interpolate between the two nearest levels |
28 | |
29 | kLast = kLinear, |
30 | }; |
31 | static constexpr int kSkMipmapModeCount = static_cast<int>(SkMipmapMode::kLast) + 1; |
32 | |
33 | /* |
34 | * Specify B and C (each between 0...1) to create a shader that applies the corresponding |
35 | * cubic reconstruction filter to the image. |
36 | * |
37 | * Example values: |
38 | * B = 1/3, C = 1/3 "Mitchell" filter |
39 | * B = 0, C = 1/2 "Catmull-Rom" filter |
40 | * |
41 | * See "Reconstruction Filters in Computer Graphics" |
42 | * Don P. Mitchell |
43 | * Arun N. Netravali |
44 | * 1988 |
45 | * https://www.cs.utexas.edu/~fussell/courses/cs384g-fall2013/lectures/mitchell/Mitchell.pdf |
46 | * |
47 | * Desmos worksheet https://www.desmos.com/calculator/aghdpicrvr |
48 | * Nice overview https://entropymine.com/imageworsener/bicubic/ |
49 | */ |
50 | struct SkCubicResampler { |
51 | float B, C; |
52 | |
53 | // Historic default for kHigh_SkFilterQuality |
54 | static constexpr SkCubicResampler Mitchell() { return {.B: 1/3.0f, .C: 1/3.0f}; } |
55 | static constexpr SkCubicResampler CatmullRom() { return {.B: 0.0f, .C: 1/2.0f}; } |
56 | }; |
57 | |
58 | struct SK_API SkSamplingOptions { |
59 | const int maxAniso = 0; |
60 | const bool useCubic = false; |
61 | const SkCubicResampler cubic = {.B: 0, .C: 0}; |
62 | const SkFilterMode filter = SkFilterMode::kNearest; |
63 | const SkMipmapMode mipmap = SkMipmapMode::kNone; |
64 | |
65 | constexpr SkSamplingOptions() = default; |
66 | SkSamplingOptions(const SkSamplingOptions&) = default; |
67 | SkSamplingOptions& operator=(const SkSamplingOptions& that) { |
68 | this->~SkSamplingOptions(); // A pedantic no-op. |
69 | new (this) SkSamplingOptions(that); |
70 | return *this; |
71 | } |
72 | |
73 | constexpr SkSamplingOptions(SkFilterMode fm, SkMipmapMode mm) |
74 | : filter(fm) |
75 | , mipmap(mm) {} |
76 | |
77 | // These are intentionally implicit because the single parameter clearly conveys what the |
78 | // implicitly created SkSamplingOptions will be. |
79 | constexpr SkSamplingOptions(SkFilterMode fm) |
80 | : filter(fm) |
81 | , mipmap(SkMipmapMode::kNone) {} |
82 | |
83 | constexpr SkSamplingOptions(const SkCubicResampler& c) |
84 | : useCubic(true) |
85 | , cubic(c) {} |
86 | |
87 | static constexpr SkSamplingOptions Aniso(int maxAniso) { |
88 | return SkSamplingOptions{std::max(a: maxAniso, b: 1)}; |
89 | } |
90 | |
91 | bool operator==(const SkSamplingOptions& other) const { |
92 | return maxAniso == other.maxAniso |
93 | && useCubic == other.useCubic |
94 | && cubic.B == other.cubic.B |
95 | && cubic.C == other.cubic.C |
96 | && filter == other.filter |
97 | && mipmap == other.mipmap; |
98 | } |
99 | bool operator!=(const SkSamplingOptions& other) const { return !(*this == other); } |
100 | |
101 | bool isAniso() const { return maxAniso != 0; } |
102 | |
103 | private: |
104 | constexpr SkSamplingOptions(int maxAniso) : maxAniso(maxAniso) {} |
105 | }; |
106 | |
107 | #endif |
108 | |