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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/Layer.h"
9 
10 #include "modules/skottie/src/Camera.h"
11 #include "modules/skottie/src/Composition.h"
12 #include "modules/skottie/src/SkottieJson.h"
13 #include "modules/skottie/src/effects/Effects.h"
14 #include "modules/skottie/src/effects/MotionBlurEffect.h"
15 #include "modules/sksg/include/SkSGClipEffect.h"
16 #include "modules/sksg/include/SkSGDraw.h"
17 #include "modules/sksg/include/SkSGGroup.h"
18 #include "modules/sksg/include/SkSGMaskEffect.h"
19 #include "modules/sksg/include/SkSGMerge.h"
20 #include "modules/sksg/include/SkSGPaint.h"
21 #include "modules/sksg/include/SkSGPath.h"
22 #include "modules/sksg/include/SkSGRect.h"
23 #include "modules/sksg/include/SkSGRenderEffect.h"
24 #include "modules/sksg/include/SkSGRenderNode.h"
25 #include "modules/sksg/include/SkSGTransform.h"
26 
27 namespace skottie {
28 namespace internal {
29 
30 namespace  {
31 
32 struct MaskInfo {
33     SkBlendMode       fBlendMode;      // used when masking with layers/blending
34     sksg::Merge::Mode fMergeMode;      // used when clipping
35     bool              fInvertGeometry;
36 };
37 
GetMaskInfo(char mode)38 const MaskInfo* GetMaskInfo(char mode) {
39     static constexpr MaskInfo k_add_info =
40         { SkBlendMode::kSrcOver   , sksg::Merge::Mode::kUnion     , false };
41     static constexpr MaskInfo k_int_info =
42         { SkBlendMode::kSrcIn     , sksg::Merge::Mode::kIntersect , false };
43     static constexpr MaskInfo k_sub_info =
44         { SkBlendMode::kDstOut    , sksg::Merge::Mode::kDifference, true  };
45     static constexpr MaskInfo k_dif_info =
46         { SkBlendMode::kXor       , sksg::Merge::Mode::kXOR       , false };
47 
48     switch (mode) {
49     case 'a': return &k_add_info;
50     case 'f': return &k_dif_info;
51     case 'i': return &k_int_info;
52     case 's': return &k_sub_info;
53     default: break;
54     }
55 
56     return nullptr;
57 }
58 
59 class MaskAdapter final : public AnimatablePropertyContainer {
60 public:
MaskAdapter(const skjson::ObjectValue & jmask,const AnimationBuilder & abuilder,SkBlendMode bm)61     MaskAdapter(const skjson::ObjectValue& jmask, const AnimationBuilder& abuilder, SkBlendMode bm)
62         : fMaskPaint(sksg::Color::Make(SK_ColorBLACK))
63         , fBlendMode(bm)
64     {
65         fMaskPaint->setAntiAlias(true);
66         if (!this->requires_isolation()) {
67             // We can mask at draw time.
68             fMaskPaint->setBlendMode(bm);
69         }
70 
71         this->bind(abuilder, jmask["o"], fOpacity);
72 
73         if (this->bind(abuilder, jmask["f"], fFeather)) {
74             fMaskFilter = sksg::BlurImageFilter::Make();
75         }
76     }
77 
hasEffect() const78     bool hasEffect() const {
79         return !this->isStatic()
80             || fOpacity < 100
81             || fFeather != SkV2{0,0};
82     }
83 
makeMask(sk_sp<sksg::Path> mask_path) const84     sk_sp<sksg::RenderNode> makeMask(sk_sp<sksg::Path> mask_path) const {
85         sk_sp<sksg::RenderNode> mask = sksg::Draw::Make(std::move(mask_path), fMaskPaint);
86 
87         // Optional mask blur (feather).
88         mask = sksg::ImageFilterEffect::Make(std::move(mask), fMaskFilter);
89 
90         if (this->requires_isolation()) {
91             mask = sksg::LayerEffect::Make(std::move(mask), fBlendMode);
92         }
93 
94         return mask;
95     }
96 
97 private:
onSync()98     void onSync() override {
99         fMaskPaint->setOpacity(fOpacity * 0.01f);
100         if (fMaskFilter) {
101             // Close enough to AE.
102             static constexpr SkScalar kFeatherToSigma = 0.38f;
103             fMaskFilter->setSigma({fFeather.x * kFeatherToSigma,
104                                    fFeather.y * kFeatherToSigma});
105         }
106     }
107 
requires_isolation() const108     bool requires_isolation() const {
109         SkASSERT(fBlendMode == SkBlendMode::kSrc     ||
110                  fBlendMode == SkBlendMode::kSrcOver ||
111                  fBlendMode == SkBlendMode::kSrcIn   ||
112                  fBlendMode == SkBlendMode::kDstOut  ||
113                  fBlendMode == SkBlendMode::kXor);
114 
115         // Some mask modes touch pixels outside the immediate draw geometry.
116         // These require a layer.
117         switch (fBlendMode) {
118             case (SkBlendMode::kSrcIn): return true;
119             default                   : return false;
120         }
121         SkUNREACHABLE;
122     }
123 
124     const sk_sp<sksg::PaintNode> fMaskPaint;
125     const SkBlendMode            fBlendMode;
126     sk_sp<sksg::BlurImageFilter> fMaskFilter; // optional "feather"
127 
128     Vec2Value   fFeather = {0,0};
129     ScalarValue fOpacity = 100;
130 };
131 
AttachMask(const skjson::ArrayValue * jmask,const AnimationBuilder * abuilder,sk_sp<sksg::RenderNode> childNode)132 sk_sp<sksg::RenderNode> AttachMask(const skjson::ArrayValue* jmask,
133                                    const AnimationBuilder* abuilder,
134                                    sk_sp<sksg::RenderNode> childNode) {
135     if (!jmask) return childNode;
136 
137     struct MaskRecord {
138         sk_sp<sksg::Path>  mask_path;    // for clipping and masking
139         sk_sp<MaskAdapter> mask_adapter; // for masking
140         sksg::Merge::Mode  merge_mode;   // for clipping
141     };
142 
143     SkSTArray<4, MaskRecord, true> mask_stack;
144     bool has_effect = false;
145 
146     for (const skjson::ObjectValue* m : *jmask) {
147         if (!m) continue;
148 
149         const skjson::StringValue* jmode = (*m)["mode"];
150         if (!jmode || jmode->size() != 1) {
151             abuilder->log(Logger::Level::kError, &(*m)["mode"], "Invalid mask mode.");
152             continue;
153         }
154 
155         const auto mode = *jmode->begin();
156         if (mode == 'n') {
157             // "None" masks have no effect.
158             continue;
159         }
160 
161         const auto* mask_info = GetMaskInfo(mode);
162         if (!mask_info) {
163             abuilder->log(Logger::Level::kWarning, nullptr, "Unsupported mask mode: '%c'.", mode);
164             continue;
165         }
166 
167         auto mask_path = abuilder->attachPath((*m)["pt"]);
168         if (!mask_path) {
169             abuilder->log(Logger::Level::kError, m, "Could not parse mask path.");
170             continue;
171         }
172 
173         auto mask_blend_mode = mask_info->fBlendMode;
174         auto mask_merge_mode = mask_info->fMergeMode;
175         auto mask_inverted   = ParseDefault<bool>((*m)["inv"], false);
176 
177         if (mask_stack.empty()) {
178             // First mask adjustments:
179             //   - always draw in source mode
180             //   - invert geometry if needed
181             mask_blend_mode = SkBlendMode::kSrc;
182             mask_merge_mode = sksg::Merge::Mode::kMerge;
183             mask_inverted   = mask_inverted != mask_info->fInvertGeometry;
184         }
185 
186         mask_path->setFillType(mask_inverted ? SkPathFillType::kInverseWinding
187                                              : SkPathFillType::kWinding);
188 
189         auto mask_adapter = sk_make_sp<MaskAdapter>(*m, *abuilder, mask_blend_mode);
190         abuilder->attachDiscardableAdapter(mask_adapter);
191 
192         has_effect |= mask_adapter->hasEffect();
193 
194         mask_stack.push_back({ std::move(mask_path),
195                                std::move(mask_adapter),
196                                mask_merge_mode });
197     }
198 
199 
200     if (mask_stack.empty())
201         return childNode;
202 
203     // If the masks are fully opaque, we can clip.
204     if (!has_effect) {
205         sk_sp<sksg::GeometryNode> clip_node;
206 
207         if (mask_stack.count() == 1) {
208             // Single path -> just clip.
209             clip_node = std::move(mask_stack.front().mask_path);
210         } else {
211             // Multiple clip paths -> merge.
212             std::vector<sksg::Merge::Rec> merge_recs;
213             merge_recs.reserve(SkToSizeT(mask_stack.count()));
214 
215             for (auto& mask : mask_stack) {
216                 merge_recs.push_back({std::move(mask.mask_path), mask.merge_mode });
217             }
218             clip_node = sksg::Merge::Make(std::move(merge_recs));
219         }
220 
221         return sksg::ClipEffect::Make(std::move(childNode), std::move(clip_node), true);
222     }
223 
224     // Complex masks (non-opaque or blurred) turn into a mask node stack.
225     sk_sp<sksg::RenderNode> maskNode;
226     if (mask_stack.count() == 1) {
227         // no group needed for single mask
228         const auto rec = mask_stack.front();
229         maskNode = rec.mask_adapter->makeMask(std::move(rec.mask_path));
230     } else {
231         std::vector<sk_sp<sksg::RenderNode>> masks;
232         masks.reserve(SkToSizeT(mask_stack.count()));
233         for (auto& rec : mask_stack) {
234             masks.push_back(rec.mask_adapter->makeMask(std::move(rec.mask_path)));
235         }
236 
237         maskNode = sksg::Group::Make(std::move(masks));
238     }
239 
240     return sksg::MaskEffect::Make(std::move(childNode), std::move(maskNode));
241 }
242 
243 class LayerController final : public Animator {
244 public:
LayerController(AnimatorScope && layer_animators,sk_sp<sksg::RenderNode> layer,size_t tanim_count,float in,float out)245     LayerController(AnimatorScope&& layer_animators,
246                     sk_sp<sksg::RenderNode> layer,
247                     size_t tanim_count, float in, float out)
248         : fLayerAnimators(std::move(layer_animators))
249         , fLayerNode(std::move(layer))
250         , fTransformAnimatorsCount(tanim_count)
251         , fIn(in)
252         , fOut(out) {}
253 
254 protected:
onSeek(float t)255     StateChanged onSeek(float t) override {
256         // in/out may be inverted for time-reversed layers
257         const auto active = (t >= fIn && t < fOut) || (t > fOut && t <= fIn);
258 
259         bool changed = false;
260         if (fLayerNode) {
261             changed |= (fLayerNode->isVisible() != active);
262             fLayerNode->setVisible(active);
263         }
264 
265         // When active, dispatch ticks to all layer animators.
266         // When inactive, we must still dispatch ticks to the layer transform animators
267         // (active child layers depend on transforms being updated).
268         const auto dispatch_count = active ? fLayerAnimators.size()
269                                            : fTransformAnimatorsCount;
270         for (size_t i = 0; i < dispatch_count; ++i) {
271             changed |= fLayerAnimators[i]->seek(t);
272         }
273 
274         return changed;
275     }
276 
277 private:
278     const AnimatorScope           fLayerAnimators;
279     const sk_sp<sksg::RenderNode> fLayerNode;
280     const size_t                  fTransformAnimatorsCount;
281     const float                   fIn,
282                                   fOut;
283 };
284 
285 class MotionBlurController final : public Animator {
286 public:
MotionBlurController(sk_sp<MotionBlurEffect> mbe)287     explicit MotionBlurController(sk_sp<MotionBlurEffect> mbe)
288         : fMotionBlurEffect(std::move(mbe)) {}
289 
290 protected:
291     // When motion blur is present, time ticks are not passed to layer animators
292     // but to the motion blur effect. The effect then drives the animators/scene-graph
293     // during reval and render phases.
onSeek(float t)294     StateChanged onSeek(float t) override {
295         fMotionBlurEffect->setT(t);
296         return true;
297     }
298 
299 private:
300     const sk_sp<MotionBlurEffect> fMotionBlurEffect;
301 };
302 
303 } // namespace
304 
LayerBuilder(const skjson::ObjectValue & jlayer,const SkSize & comp_size)305 LayerBuilder::LayerBuilder(const skjson::ObjectValue& jlayer, const SkSize& comp_size)
306     : fJlayer(jlayer)
307     , fIndex      (ParseDefault<int>(jlayer["ind"   ], -1))
308     , fParentIndex(ParseDefault<int>(jlayer["parent"], -1))
309     , fType       (ParseDefault<int>(jlayer["ty"    ], -1))
310     , fAutoOrient (ParseDefault<int>(jlayer["ao"    ],  0))
311     , fInfo{comp_size,
312             ParseDefault<float>(jlayer["ip"], 0.0f),
313             ParseDefault<float>(jlayer["op"], 0.0f)}
314 {
315 
316     if (this->isCamera() || ParseDefault<int>(jlayer["ddd"], 0)) {
317         fFlags |= Flags::kIs3D;
318     }
319 }
320 
321 LayerBuilder::~LayerBuilder() = default;
322 
isCamera() const323 bool LayerBuilder::isCamera() const {
324     static constexpr int kCameraLayerType = 13;
325 
326     return fType == kCameraLayerType;
327 }
328 
buildTransform(const AnimationBuilder & abuilder,CompositionBuilder * cbuilder)329 sk_sp<sksg::Transform> LayerBuilder::buildTransform(const AnimationBuilder& abuilder,
330                                                     CompositionBuilder* cbuilder) {
331     // Depending on the leaf node type, we treat the whole transform chain as either 2D or 3D.
332     const auto transform_chain_type = this->is3D() ? TransformType::k3D
333                                                    : TransformType::k2D;
334     fLayerTransform = this->getTransform(abuilder, cbuilder, transform_chain_type);
335 
336     return fLayerTransform;
337 }
338 
getTransform(const AnimationBuilder & abuilder,CompositionBuilder * cbuilder,TransformType ttype)339 sk_sp<sksg::Transform> LayerBuilder::getTransform(const AnimationBuilder& abuilder,
340                                                   CompositionBuilder* cbuilder,
341                                                   TransformType ttype) {
342     const auto cache_valid_mask = (1ul << ttype);
343     if (!(fFlags & cache_valid_mask)) {
344         // Set valid flag upfront to break cycles.
345         fFlags |= cache_valid_mask;
346 
347         const AnimationBuilder::AutoPropertyTracker apt(&abuilder, fJlayer, PropertyObserver::NodeType::LAYER);
348         AnimationBuilder::AutoScope ascope(&abuilder, std::move(fLayerScope));
349         fTransformCache[ttype] = this->doAttachTransform(abuilder, cbuilder, ttype);
350         fLayerScope = ascope.release();
351         fTransformAnimatorCount = fLayerScope.size();
352     }
353 
354     return fTransformCache[ttype];
355 }
356 
getParentTransform(const AnimationBuilder & abuilder,CompositionBuilder * cbuilder,TransformType ttype)357 sk_sp<sksg::Transform> LayerBuilder::getParentTransform(const AnimationBuilder& abuilder,
358                                                         CompositionBuilder* cbuilder,
359                                                         TransformType ttype) {
360     if (auto* parent_builder = cbuilder->layerBuilder(fParentIndex)) {
361         // Explicit parent layer.
362         return parent_builder->getTransform(abuilder, cbuilder, ttype);
363     }
364 
365     if (ttype == TransformType::k3D) {
366         // During camera transform attachment, cbuilder->getCameraTransform() is null.
367         // This prevents camera->camera transform chain cycles.
368         SkASSERT(!this->isCamera() || !cbuilder->getCameraTransform());
369 
370         // 3D transform chains are implicitly rooted onto the camera.
371         return cbuilder->getCameraTransform();
372     }
373 
374     return nullptr;
375 }
376 
doAttachTransform(const AnimationBuilder & abuilder,CompositionBuilder * cbuilder,TransformType ttype)377 sk_sp<sksg::Transform> LayerBuilder::doAttachTransform(const AnimationBuilder& abuilder,
378                                                        CompositionBuilder* cbuilder,
379                                                        TransformType ttype) {
380     const skjson::ObjectValue* jtransform = fJlayer["ks"];
381     if (!jtransform) {
382         return nullptr;
383     }
384 
385     auto parent_transform = this->getParentTransform(abuilder, cbuilder, ttype);
386 
387     if (this->isCamera()) {
388         // parent_transform applies to the camera itself => it pre-composes inverted to the
389         // camera/view/adapter transform.
390         //
391         //   T_camera' = T_camera x Inv(parent_transform)
392         //
393         return abuilder.attachCamera(fJlayer,
394                                      *jtransform,
395                                      sksg::Transform::MakeInverse(std::move(parent_transform)),
396                                      cbuilder->fSize);
397     }
398 
399     return this->is3D()
400             ? abuilder.attachMatrix3D(*jtransform, std::move(parent_transform), fAutoOrient)
401             : abuilder.attachMatrix2D(*jtransform, std::move(parent_transform), fAutoOrient);
402 }
403 
hasMotionBlur(const CompositionBuilder * cbuilder) const404 bool LayerBuilder::hasMotionBlur(const CompositionBuilder* cbuilder) const {
405     return cbuilder->fMotionBlurSamples > 1
406         && cbuilder->fMotionBlurAngle   > 0
407         && ParseDefault(fJlayer["mb"], false);
408 }
409 
buildRenderTree(const AnimationBuilder & abuilder,CompositionBuilder * cbuilder,const LayerBuilder * prev_layer)410 sk_sp<sksg::RenderNode> LayerBuilder::buildRenderTree(const AnimationBuilder& abuilder,
411                                                       CompositionBuilder* cbuilder,
412                                                       const LayerBuilder* prev_layer) {
413     const AnimationBuilder::AutoPropertyTracker apt(&abuilder, fJlayer, PropertyObserver::NodeType::LAYER);
414 
415     using LayerBuilder =
416         sk_sp<sksg::RenderNode> (AnimationBuilder::*)(const skjson::ObjectValue&,
417                                                       AnimationBuilder::LayerInfo*) const;
418 
419     // AE is annoyingly inconsistent in how effects interact with layer transforms: depending on
420     // the layer type, effects are applied before or after the content is transformed.
421     //
422     // Empirically, pre-rendered layers (for some loose meaning of "pre-rendered") are in the
423     // former category (effects are subject to transformation), while the remaining types are in
424     // the latter.
425     enum : uint32_t {
426         kTransformEffects = 0x01, // The layer transform also applies to its effects.
427         kForceSeek        = 0x02, // Dispatch all seek() events even when the layer is inactive.
428     };
429 
430     static constexpr struct {
431         LayerBuilder                      fBuilder;
432         uint32_t                          fFlags;
433     } gLayerBuildInfo[] = {
434         { &AnimationBuilder::attachPrecompLayer, kTransformEffects },  // 'ty':  0 -> precomp
435         { &AnimationBuilder::attachSolidLayer  , kTransformEffects },  // 'ty':  1 -> solid
436         { &AnimationBuilder::attachFootageLayer, kTransformEffects },  // 'ty':  2 -> image
437         { &AnimationBuilder::attachNullLayer   ,                 0 },  // 'ty':  3 -> null
438         { &AnimationBuilder::attachShapeLayer  ,                 0 },  // 'ty':  4 -> shape
439         { &AnimationBuilder::attachTextLayer   ,                 0 },  // 'ty':  5 -> text
440         { &AnimationBuilder::attachAudioLayer  ,        kForceSeek },  // 'ty':  6 -> audio
441         { nullptr                              ,                 0 },  // 'ty':  7 -> pholderVideo
442         { nullptr                              ,                 0 },  // 'ty':  8 -> imageSeq
443         { &AnimationBuilder::attachFootageLayer, kTransformEffects },  // 'ty':  9 -> video
444         { nullptr                              ,                 0 },  // 'ty': 10 -> pholderStill
445         { nullptr                              ,                 0 },  // 'ty': 11 -> guide
446         { nullptr                              ,                 0 },  // 'ty': 12 -> adjustment
447         { &AnimationBuilder::attachNullLayer   ,                 0 },  // 'ty': 13 -> camera
448         { nullptr                              ,                 0 },  // 'ty': 14 -> light
449     };
450 
451     const auto type = SkToSizeT(fType);
452     if (type >= SK_ARRAY_COUNT(gLayerBuildInfo)) {
453         return nullptr;
454     }
455 
456     const auto& build_info = gLayerBuildInfo[type];
457 
458     // Switch to the layer animator scope (which at this point holds transform-only animators).
459     AnimationBuilder::AutoScope ascope(&abuilder, std::move(fLayerScope));
460 
461     // Potentially null.
462     sk_sp<sksg::RenderNode> layer;
463 
464     // Build the layer content fragment.
465     if (build_info.fBuilder) {
466         layer = (abuilder.*(build_info.fBuilder))(fJlayer, &fInfo);
467     }
468 
469     // Clip layers with explicit dimensions.
470     float w = 0, h = 0;
471     if (Parse<float>(fJlayer["w"], &w) && Parse<float>(fJlayer["h"], &h)) {
472         layer = sksg::ClipEffect::Make(std::move(layer),
473                                        sksg::Rect::Make(SkRect::MakeWH(w, h)),
474                                        true);
475     }
476 
477     // Optional layer mask.
478     layer = AttachMask(fJlayer["masksProperties"], &abuilder, std::move(layer));
479 
480     // Does the transform apply to effects also?
481     // (AE quirk: it doesn't - except for solid layers)
482     const auto transform_effects = (build_info.fFlags & kTransformEffects);
483 
484     // Attach the transform before effects, when needed.
485     if (fLayerTransform && !transform_effects) {
486         layer = sksg::TransformEffect::Make(std::move(layer), fLayerTransform);
487     }
488 
489     // Optional layer effects.
490     if (const skjson::ArrayValue* jeffects = fJlayer["ef"]) {
491         layer = EffectBuilder(&abuilder, fInfo.fSize, cbuilder)
492                 .attachEffects(*jeffects, std::move(layer));
493     }
494 
495     // Attach the transform after effects, when needed.
496     if (fLayerTransform && transform_effects) {
497         layer = sksg::TransformEffect::Make(std::move(layer), std::move(fLayerTransform));
498     }
499 
500     // Optional layer styles.
501     if (const skjson::ArrayValue* jstyles = fJlayer["sy"]) {
502         layer = EffectBuilder(&abuilder, fInfo.fSize, cbuilder)
503                 .attachStyles(*jstyles, std::move(layer));
504     }
505 
506     // Optional layer opacity.
507     // TODO: de-dupe this "ks" lookup with matrix above.
508     if (const skjson::ObjectValue* jtransform = fJlayer["ks"]) {
509         layer = abuilder.attachOpacity(*jtransform, std::move(layer));
510     }
511 
512     // Stash the content tree in case it is needed for later mattes.
513     fContentTree = layer;
514     if (ParseDefault<bool>(fJlayer["hd"], false)) {
515         layer = nullptr;
516     }
517 
518     const auto has_animators    = !abuilder.fCurrentAnimatorScope->empty();
519     const auto force_seek_count = build_info.fFlags & kForceSeek
520             ? abuilder.fCurrentAnimatorScope->size()
521             : fTransformAnimatorCount;
522 
523     sk_sp<Animator> controller = sk_make_sp<LayerController>(ascope.release(),
524                                                              layer,
525                                                              force_seek_count,
526                                                              fInfo.fInPoint,
527                                                              fInfo.fOutPoint);
528 
529     // Optional motion blur.
530     if (layer && has_animators && this->hasMotionBlur(cbuilder)) {
531         // Wrap both the layer node and the controller.
532         auto motion_blur = MotionBlurEffect::Make(std::move(controller), std::move(layer),
533                                                   cbuilder->fMotionBlurSamples,
534                                                   cbuilder->fMotionBlurAngle,
535                                                   cbuilder->fMotionBlurPhase);
536         controller = sk_make_sp<MotionBlurController>(motion_blur);
537         layer = std::move(motion_blur);
538     }
539 
540     abuilder.fCurrentAnimatorScope->push_back(std::move(controller));
541 
542     if (ParseDefault<bool>(fJlayer["td"], false)) {
543         // |layer| is a track matte.  We apply it as a mask to the next layer.
544         return nullptr;
545     }
546 
547     // Optional matte.
548     const auto matte_mode = prev_layer
549             ? ParseDefault<size_t>(fJlayer["tt"], 0)
550             : 0;
551     if (matte_mode > 0) {
552         static constexpr sksg::MaskEffect::Mode gMatteModes[] = {
553             sksg::MaskEffect::Mode::kAlphaNormal, // tt: 1
554             sksg::MaskEffect::Mode::kAlphaInvert, // tt: 2
555             sksg::MaskEffect::Mode::kLumaNormal,  // tt: 3
556             sksg::MaskEffect::Mode::kLumaInvert,  // tt: 4
557         };
558 
559         if (matte_mode <= SK_ARRAY_COUNT(gMatteModes)) {
560             // The current layer is masked with the previous layer *content*.
561             layer = sksg::MaskEffect::Make(std::move(layer),
562                                            prev_layer->fContentTree,
563                                            gMatteModes[matte_mode - 1]);
564         } else {
565             abuilder.log(Logger::Level::kError, nullptr,
566                          "Unknown track matte mode: %zu\n", matte_mode);
567         }
568     }
569 
570     // Finally, attach an optional blend mode.
571     // NB: blend modes are never applied to matte sources (layer content only).
572     return abuilder.attachBlendMode(fJlayer, std::move(layer));
573 }
574 
575 } // namespace internal
576 } // namespace skottie
577