1 /*
2 * Copyright 2019 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 #include "modules/skottie/src/effects/Effects.h"
9
10 #include "include/effects/SkTableColorFilter.h"
11 #include "modules/skottie/src/SkottieAdapter.h"
12 #include "modules/skottie/src/SkottieValue.h"
13 #include "modules/sksg/include/SkSGColorFilter.h"
14 #include "src/utils/SkJSON.h"
15
16 #include <cmath>
17
18 namespace skottie {
19 namespace internal {
20
21 // Levels color correction effect.
22 //
23 // Maps the selected channels from [inBlack...inWhite] to [outBlack, outWhite],
24 // based on a gamma exponent.
25 //
26 // For [i0..i1] -> [o0..o1]:
27 //
28 // c' = o0 + (o1 - o0) * ((c - i0) / (i1 - i0)) ^ G
29 //
30 // The output is optionally clipped to the output range.
31 //
32 // In/out intervals are clampped to [0..1]. Inversion is allowed.
33
34 namespace {
35
36 class LevelsEffectAdapter final : public SkNVRefCnt<LevelsEffectAdapter> {
37 public:
LevelsEffectAdapter(sk_sp<sksg::RenderNode> child)38 explicit LevelsEffectAdapter(sk_sp<sksg::RenderNode> child)
39 : fEffect(sksg::ExternalColorFilter::Make(std::move(child))) {
40 SkASSERT(fEffect);
41 }
42
43 // 1: RGB, 2: R, 3: G, 4: B, 5: A
44 ADAPTER_PROPERTY( Channel, SkScalar, 1)
45 ADAPTER_PROPERTY( InBlack, SkScalar, 0)
46 ADAPTER_PROPERTY( InWhite, SkScalar, 1)
47 ADAPTER_PROPERTY( OutBlack, SkScalar, 0)
48 ADAPTER_PROPERTY( OutWhite, SkScalar, 1)
49 ADAPTER_PROPERTY( Gamma, SkScalar, 1)
50 // 1: clip, 2,3: don't clip
51 ADAPTER_PROPERTY(ClipBlack, SkScalar, 1)
52 ADAPTER_PROPERTY(ClipWhite, SkScalar, 1)
53
root() const54 const sk_sp<sksg::ExternalColorFilter>& root() const { return fEffect; }
55
56 private:
apply()57 void apply() {
58 enum LottieChannel {
59 kRGB_Channel = 1,
60 kR_Channel = 2,
61 kG_Channel = 3,
62 kB_Channel = 4,
63 kA_Channel = 5,
64 };
65
66 const auto channel = SkScalarTruncToInt(fChannel);
67 if (channel < kRGB_Channel || channel > kA_Channel) {
68 fEffect->setColorFilter(nullptr);
69 return;
70 }
71
72 auto in_0 = SkTPin(fInBlack, 0.0f, 1.0f),
73 in_1 = SkTPin(fInWhite, 0.0f, 1.0f),
74 out_0 = SkTPin(fOutBlack, 0.0f, 1.0f),
75 out_1 = SkTPin(fOutWhite, 0.0f, 1.0f),
76 g = sk_ieee_float_divide(1, std::max(fGamma, 0.0f));
77
78 float clip[] = {0, 1};
79 const auto kLottieDoClip = 1;
80 if (SkScalarTruncToInt(fClipBlack) == kLottieDoClip) {
81 const auto idx = fOutBlack <= fOutWhite ? 0 : 1;
82 clip[idx] = out_0;
83 }
84 if (SkScalarTruncToInt(fClipWhite) == kLottieDoClip) {
85 const auto idx = fOutBlack <= fOutWhite ? 1 : 0;
86 clip[idx] = out_1;
87 }
88 SkASSERT(clip[0] <= clip[1]);
89
90 auto dIn = in_1 - in_0,
91 dOut = out_1 - out_0;
92
93 if (SkScalarNearlyZero(dIn)) {
94 // Degenerate dIn == 0 makes the arithmetic below explode.
95 //
96 // We could specialize the builder to deal with that case, or we could just
97 // nudge by epsilon to make it all work. The latter approach is simpler
98 // and doesn't have any noticeable downsides.
99 //
100 // Also nudge in_0 towards 0.5, in case it was sqashed against an extremity.
101 // This allows for some abrupt transition when the output interval is not
102 // collapsed, and produces results closer to AE.
103 static constexpr auto kEpsilon = 2 * SK_ScalarNearlyZero;
104 dIn += std::copysign(kEpsilon, dIn);
105 in_0 += std::copysign(kEpsilon, .5f - in_0);
106 SkASSERT(!SkScalarNearlyZero(dIn));
107 }
108
109 uint8_t lut[256];
110
111 auto t = -in_0 / dIn,
112 dT = 1 / 255.0f / dIn;
113
114 // TODO: is linear gamma common-enough to warrant a fast path?
115 for (size_t i = 0; i < 256; ++i) {
116 const auto out = out_0 + dOut * std::pow(std::max(t, 0.0f), g);
117 SkASSERT(!SkScalarIsNaN(out));
118
119 lut[i] = static_cast<uint8_t>(std::round(SkTPin(out, clip[0], clip[1]) * 255));
120
121 t += dT;
122 }
123
124 fEffect->setColorFilter(SkTableColorFilter::MakeARGB(
125 channel == kA_Channel ? lut : nullptr,
126 channel == kR_Channel || channel == kRGB_Channel ? lut : nullptr,
127 channel == kG_Channel || channel == kRGB_Channel ? lut : nullptr,
128 channel == kB_Channel || channel == kRGB_Channel ? lut : nullptr
129 ));
130 }
131
132 sk_sp<sksg::ExternalColorFilter> fEffect;
133 };
134
135 } // anonymous ns
136
attachLevelsEffect(const skjson::ArrayValue & jprops,sk_sp<sksg::RenderNode> layer) const137 sk_sp<sksg::RenderNode> EffectBuilder::attachLevelsEffect(const skjson::ArrayValue& jprops,
138 sk_sp<sksg::RenderNode> layer) const {
139 enum : size_t {
140 kChannel_Index = 0,
141 // ??? = 1,
142 kInputBlack_Index = 2,
143 kInputWhite_Index = 3,
144 kGamma_Index = 4,
145 kOutputBlack_Index = 5,
146 kOutputWhite_Index = 6,
147 kClipToOutBlack_Index = 7,
148 kClipToOutWhite_Index = 8,
149 };
150
151 auto adapter = sk_make_sp<LevelsEffectAdapter>(std::move(layer));
152
153 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kChannel_Index),
154 [adapter](const ScalarValue& channel) {
155 adapter->setChannel(channel);
156 });
157 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kInputBlack_Index),
158 [adapter](const ScalarValue& ib) {
159 adapter->setInBlack(ib);
160 });
161 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kInputWhite_Index),
162 [adapter](const ScalarValue& iw) {
163 adapter->setInWhite(iw);
164 });
165 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kOutputBlack_Index),
166 [adapter](const ScalarValue& ob) {
167 adapter->setOutBlack(ob);
168 });
169 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kOutputWhite_Index),
170 [adapter](const ScalarValue& ow) {
171 adapter->setOutWhite(ow);
172 });
173 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kGamma_Index),
174 [adapter](const ScalarValue& g) {
175 adapter->setGamma(g);
176 });
177
178 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kClipToOutBlack_Index),
179 [adapter](const ScalarValue& cb) {
180 adapter->setClipBlack(cb);
181 });
182 fBuilder->bindProperty<ScalarValue>(GetPropValue(jprops, kClipToOutWhite_Index),
183 [adapter](const ScalarValue& cw) {
184 adapter->setClipWhite(cw);
185 });
186
187 return adapter->root();
188 }
189
190 } // namespace internal
191 } // namespace skottie
192