submodule/skia/src/utils/SkShadowUtils.cpp

   1 /*
   2 * Copyright 2017 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 "include/utils/SkShadowUtils.h"
   9
  10 #include "include/core/SkBlendMode.h"
  11 #include "include/core/SkBlender.h"
  12 #include "include/core/SkBlurTypes.h"
  13 #include "include/core/SkCanvas.h"
  14 #include "include/core/SkColorFilter.h"
  15 #include "include/core/SkFlattenable.h"
  16 #include "include/core/SkMaskFilter.h"
  17 #include "include/core/SkMatrix.h"
  18 #include "include/core/SkPaint.h"
  19 #include "include/core/SkPath.h"
  20 #include "include/core/SkPoint.h"
  21 #include "include/core/SkPoint3.h"
  22 #include "include/core/SkRect.h"
  23 #include "include/core/SkRefCnt.h"
  24 #include "include/core/SkVertices.h"
  25 #include "include/private/SkIDChangeListener.h"
  26 #include "include/private/SkTPin.h"
  27 #include "include/private/SkTemplates.h"
  28 #include "include/utils/SkRandom.h"
  29 #include "src/core/SkBlurMask.h"
  30 #include "src/core/SkColorFilterBase.h"
  31 #include "src/core/SkColorFilterPriv.h"
  32 #include "src/core/SkDevice.h"
  33 #include "src/core/SkDrawShadowInfo.h"
  34 #include "src/core/SkEffectPriv.h"
  35 #include "src/core/SkPathPriv.h"
  36 #include "src/core/SkRasterPipeline.h"
  37 #include "src/core/SkResourceCache.h"
  38 #include "src/core/SkVM.h"
  39 #include "src/core/SkVerticesPriv.h"
  40 #include "src/utils/SkShadowTessellator.h"
  41
  42 #if SK_SUPPORT_GPU
  43 #include "include/effects/SkRuntimeEffect.h"
  44 #include "src/core/SkRuntimeEffectPriv.h"
  45 #include "src/gpu/ganesh/GrFragmentProcessor.h"
  46 #include "src/gpu/ganesh/GrStyle.h"
  47 #include "src/gpu/ganesh/effects/GrSkSLFP.h"
  48 #include "src/gpu/ganesh/geometry/GrStyledShape.h"
  49
  50 class GrColorInfo;
  51 class GrRecordingContext;
  52 #endif
  53
  54 #include <string.h>
  55 #include <algorithm>
  56 #include <cstdint>
  57 #include <functional>
  58 #include <memory>
  59 #include <new>
  60 #include <utility>
  61
  62 class SkArenaAlloc;
  63 class SkColorInfo;
  64 class SkRRect;
  65 class SkReadBuffer;
  66 class SkWriteBuffer;
  67
  68 /**
  69 *  Gaussian color filter -- produces a Gaussian ramp based on the color's B value,
  70 *                           then blends with the color's G value.
  71 *                           Final result is black with alpha of Gaussian(B)*G.
  72 *                           The assumption is that the original color's alpha is 1.
  73 */
  74 class SkGaussianColorFilter : public SkColorFilterBase {
  75 public:
  76     SkGaussianColorFilter() : INHERITED() {}
  77
  78 #if SK_SUPPORT_GPU
  79     GrFPResult asFragmentProcessor(std::unique_ptr<GrFragmentProcessor> inputFP,
  80                                    GrRecordingContext*, const GrColorInfo&) const override;
  81 #endif
  82
  83 protected:
  84     void flatten(SkWriteBuffer&) const override {}
  85     bool onAppendStages(const SkStageRec& rec, bool shaderIsOpaque) const override {
  86         rec.fPipeline->append(SkRasterPipeline::gauss_a_to_rgba);
  87         return true;
  88     }
  89
  90     skvm::Color onProgram(skvm::Builder* p, skvm::Color c, const SkColorInfo& dst, skvm::Uniforms*,
  91                           SkArenaAlloc*) const override {
  92         // x = 1 - x;
  93         // exp(-x * x * 4) - 0.018f;
  94         // ... now approximate with quartic
  95         //
  96         skvm::F32 x = p->splat(-2.26661229133605957031f);
  97                   x = c.a * x + 2.89795351028442382812f;
  98                   x = c.a * x + 0.21345567703247070312f;
  99                   x = c.a * x + 0.15489584207534790039f;
 100                   x = c.a * x + 0.00030726194381713867f;
 101         return {x, x, x, x};
 102     }
 103
 104 private:
 105     SK_FLATTENABLE_HOOKS(SkGaussianColorFilter)
 106
 107     using INHERITED = SkColorFilterBase;
 108 };
 109
 110 sk_sp<SkFlattenable> SkGaussianColorFilter::CreateProc(SkReadBuffer&) {
 111     return SkColorFilterPriv::MakeGaussian();
 112 }
 113
 114 #if SK_SUPPORT_GPU
 115
 116 GrFPResult SkGaussianColorFilter::asFragmentProcessor(std::unique_ptr<GrFragmentProcessor> inputFP,
 117                                                       GrRecordingContext*,
 118                                                       const GrColorInfo&) const {
 119     static auto effect = SkMakeRuntimeEffect(SkRuntimeEffect::MakeForColorFilter, R"(
 120         half4 main(half4 inColor) {
 121             half factor = 1 - inColor.a;
 122             factor = exp(-factor * factor * 4) - 0.018;
 123             return half4(factor);
 124         }
 125     )");
 126     SkASSERT(SkRuntimeEffectPriv::SupportsConstantOutputForConstantInput(effect));
 127     return GrFPSuccess(
 128             GrSkSLFP::Make(effect, "gaussian_fp", std::move(inputFP), GrSkSLFP::OptFlags::kNone));
 129 }
 130 #endif
 131
 132 sk_sp<SkColorFilter> SkColorFilterPriv::MakeGaussian() {
 133     return sk_sp<SkColorFilter>(new SkGaussianColorFilter);
 134 }
 135
 136 ///////////////////////////////////////////////////////////////////////////////////////////////////
 137
 138 namespace {
 139
 140 uint64_t resource_cache_shared_id() {
 141     return 0x2020776f64616873llu;  // 'shadow  '
 142 }
 143
 144 /** Factory for an ambient shadow mesh with particular shadow properties. */
 145 struct AmbientVerticesFactory {
 146     SkScalar fOccluderHeight = SK_ScalarNaN;  // NaN so that isCompatible will fail until init'ed.
 147     bool fTransparent;
 148     SkVector fOffset;
 149
 150     bool isCompatible(const AmbientVerticesFactory& that, SkVector* translate) const {
 151         if (fOccluderHeight != that.fOccluderHeight || fTransparent != that.fTransparent) {
 152             return false;
 153         }
 154         *translate = that.fOffset;
 155         return true;
 156     }
 157
 158     sk_sp<SkVertices> makeVertices(const SkPath& path, const SkMatrix& ctm,
 159                                    SkVector* translate) const {
 160         SkPoint3 zParams = SkPoint3::Make(0, 0, fOccluderHeight);
 161         // pick a canonical place to generate shadow
 162         SkMatrix noTrans(ctm);
 163         if (!ctm.hasPerspective()) {
 164             noTrans[SkMatrix::kMTransX] = 0;
 165             noTrans[SkMatrix::kMTransY] = 0;
 166         }
 167         *translate = fOffset;
 168         return SkShadowTessellator::MakeAmbient(path, noTrans, zParams, fTransparent);
 169     }
 170 };
 171
 172 /** Factory for an spot shadow mesh with particular shadow properties. */
 173 struct SpotVerticesFactory {
 174     enum class OccluderType {
 175         // The umbra cannot be dropped out because either the occluder is not opaque,
 176         // or the center of the umbra is visible. Uses point light.
 177         kPointTransparent,
 178         // The umbra can be dropped where it is occluded. Uses point light.
 179         kPointOpaquePartialUmbra,
 180         // It is known that the entire umbra is occluded. Uses point light.
 181         kPointOpaqueNoUmbra,
 182         // Uses directional light.
 183         kDirectional,
 184         // The umbra can't be dropped out. Uses directional light.
 185         kDirectionalTransparent,
 186     };
 187
 188     SkVector fOffset;
 189     SkPoint  fLocalCenter;
 190     SkScalar fOccluderHeight = SK_ScalarNaN; // NaN so that isCompatible will fail until init'ed.
 191     SkPoint3 fDevLightPos;
 192     SkScalar fLightRadius;
 193     OccluderType fOccluderType;
 194
 195     bool isCompatible(const SpotVerticesFactory& that, SkVector* translate) const {
 196         if (fOccluderHeight != that.fOccluderHeight || fDevLightPos.fZ != that.fDevLightPos.fZ ||
 197             fLightRadius != that.fLightRadius || fOccluderType != that.fOccluderType) {
 198             return false;
 199         }
 200         switch (fOccluderType) {
 201             case OccluderType::kPointTransparent:
 202             case OccluderType::kPointOpaqueNoUmbra:
 203                 // 'this' and 'that' will either both have no umbra removed or both have all the
 204                 // umbra removed.
 205                 *translate = that.fOffset;
 206                 return true;
 207             case OccluderType::kPointOpaquePartialUmbra:
 208                 // In this case we partially remove the umbra differently for 'this' and 'that'
 209                 // if the offsets don't match.
 210                 if (fOffset == that.fOffset) {
 211                     translate->set(0, 0);
 212                     return true;
 213                 }
 214                 return false;
 215             case OccluderType::kDirectional:
 216             case OccluderType::kDirectionalTransparent:
 217                 *translate = that.fOffset - fOffset;
 218                 return true;
 219         }
 220         SK_ABORT("Uninitialized occluder type?");
 221     }
 222
 223     sk_sp<SkVertices> makeVertices(const SkPath& path, const SkMatrix& ctm,
 224                                    SkVector* translate) const {
 225         bool transparent = fOccluderType == OccluderType::kPointTransparent ||
 226                            fOccluderType == OccluderType::kDirectionalTransparent;
 227         bool directional = fOccluderType == OccluderType::kDirectional ||
 228                            fOccluderType == OccluderType::kDirectionalTransparent;
 229         SkPoint3 zParams = SkPoint3::Make(0, 0, fOccluderHeight);
 230         if (directional) {
 231             translate->set(0, 0);
 232             return SkShadowTessellator::MakeSpot(path, ctm, zParams, fDevLightPos, fLightRadius,
 233                                                  transparent, true);
 234         } else if (ctm.hasPerspective() || OccluderType::kPointOpaquePartialUmbra == fOccluderType) {
 235             translate->set(0, 0);
 236             return SkShadowTessellator::MakeSpot(path, ctm, zParams, fDevLightPos, fLightRadius,
 237                                                  transparent, false);
 238         } else {
 239             // pick a canonical place to generate shadow, with light centered over path
 240             SkMatrix noTrans(ctm);
 241             noTrans[SkMatrix::kMTransX] = 0;
 242             noTrans[SkMatrix::kMTransY] = 0;
 243             SkPoint devCenter(fLocalCenter);
 244             noTrans.mapPoints(&devCenter, 1);
 245             SkPoint3 centerLightPos = SkPoint3::Make(devCenter.fX, devCenter.fY, fDevLightPos.fZ);
 246             *translate = fOffset;
 247             return SkShadowTessellator::MakeSpot(path, noTrans, zParams,
 248                                                  centerLightPos, fLightRadius, transparent, false);
 249         }
 250     }
 251 };
 252
 253 /**
 254  * This manages a set of tessellations for a given shape in the cache. Because SkResourceCache
 255  * records are immutable this is not itself a Rec. When we need to update it we return this on
 256  * the FindVisitor and let the cache destroy the Rec. We'll update the tessellations and then add
 257  * a new Rec with an adjusted size for any deletions/additions.
 258  */
 259 class CachedTessellations : public SkRefCnt {
 260 public:
 261     size_t size() const { return fAmbientSet.size() + fSpotSet.size(); }
 262
 263     sk_sp<SkVertices> find(const AmbientVerticesFactory& ambient, const SkMatrix& matrix,
 264                            SkVector* translate) const {
 265         return fAmbientSet.find(ambient, matrix, translate);
 266     }
 267
 268     sk_sp<SkVertices> add(const SkPath& devPath, const AmbientVerticesFactory& ambient,
 269                           const SkMatrix& matrix, SkVector* translate) {
 270         return fAmbientSet.add(devPath, ambient, matrix, translate);
 271     }
 272
 273     sk_sp<SkVertices> find(const SpotVerticesFactory& spot, const SkMatrix& matrix,
 274                            SkVector* translate) const {
 275         return fSpotSet.find(spot, matrix, translate);
 276     }
 277
 278     sk_sp<SkVertices> add(const SkPath& devPath, const SpotVerticesFactory& spot,
 279                           const SkMatrix& matrix, SkVector* translate) {
 280         return fSpotSet.add(devPath, spot, matrix, translate);
 281     }
 282
 283 private:
 284     template <typename FACTORY, int MAX_ENTRIES>
 285     class Set {
 286     public:
 287         size_t size() const { return fSize; }
 288
 289         sk_sp<SkVertices> find(const FACTORY& factory, const SkMatrix& matrix,
 290                                SkVector* translate) const {
 291             for (int i = 0; i < MAX_ENTRIES; ++i) {
 292                 if (fEntries[i].fFactory.isCompatible(factory, translate)) {
 293                     const SkMatrix& m = fEntries[i].fMatrix;
 294                     if (matrix.hasPerspective() || m.hasPerspective()) {
 295                         if (matrix != fEntries[i].fMatrix) {
 296                             continue;
 297                         }
 298                     } else if (matrix.getScaleX() != m.getScaleX() ||
 299                                matrix.getSkewX() != m.getSkewX() ||
 300                                matrix.getScaleY() != m.getScaleY() ||
 301                                matrix.getSkewY() != m.getSkewY()) {
 302                         continue;
 303                     }
 304                     return fEntries[i].fVertices;
 305                 }
 306             }
 307             return nullptr;
 308         }
 309
 310         sk_sp<SkVertices> add(const SkPath& path, const FACTORY& factory, const SkMatrix& matrix,
 311                               SkVector* translate) {
 312             sk_sp<SkVertices> vertices = factory.makeVertices(path, matrix, translate);
 313             if (!vertices) {
 314                 return nullptr;
 315             }
 316             int i;
 317             if (fCount < MAX_ENTRIES) {
 318                 i = fCount++;
 319             } else {
 320                 i = fRandom.nextULessThan(MAX_ENTRIES);
 321                 fSize -= fEntries[i].fVertices->approximateSize();
 322             }
 323             fEntries[i].fFactory = factory;
 324             fEntries[i].fVertices = vertices;
 325             fEntries[i].fMatrix = matrix;
 326             fSize += vertices->approximateSize();
 327             return vertices;
 328         }
 329
 330     private:
 331         struct Entry {
 332             FACTORY fFactory;
 333             sk_sp<SkVertices> fVertices;
 334             SkMatrix fMatrix;
 335         };
 336         Entry fEntries[MAX_ENTRIES];
 337         int fCount = 0;
 338         size_t fSize = 0;
 339         SkRandom fRandom;
 340     };
 341
 342     Set<AmbientVerticesFactory, 4> fAmbientSet;
 343     Set<SpotVerticesFactory, 4> fSpotSet;
 344 };
 345
 346 /**
 347  * A record of shadow vertices stored in SkResourceCache of CachedTessellations for a particular
 348  * path. The key represents the path's geometry and not any shadow params.
 349  */
 350 class CachedTessellationsRec : public SkResourceCache::Rec {
 351 public:
 352     CachedTessellationsRec(const SkResourceCache::Key& key,
 353                            sk_sp<CachedTessellations> tessellations)
 354             : fTessellations(std::move(tessellations)) {
 355         fKey.reset(new uint8_t[key.size()]);
 356         memcpy(fKey.get(), &key, key.size());
 357     }
 358
 359     const Key& getKey() const override {
 360         return *reinterpret_cast<SkResourceCache::Key*>(fKey.get());
 361     }
 362
 363     size_t bytesUsed() const override { return fTessellations->size(); }
 364
 365     const char* getCategory() const override { return "tessellated shadow masks"; }
 366
 367     sk_sp<CachedTessellations> refTessellations() const { return fTessellations; }
 368
 369     template <typename FACTORY>
 370     sk_sp<SkVertices> find(const FACTORY& factory, const SkMatrix& matrix,
 371                            SkVector* translate) const {
 372         return fTessellations->find(factory, matrix, translate);
 373     }
 374
 375 private:
 376     std::unique_ptr<uint8_t[]> fKey;
 377     sk_sp<CachedTessellations> fTessellations;
 378 };
 379
 380 /**
 381  * Used by FindVisitor to determine whether a cache entry can be reused and if so returns the
 382  * vertices and a translation vector. If the CachedTessellations does not contain a suitable
 383  * mesh then we inform SkResourceCache to destroy the Rec and we return the CachedTessellations
 384  * to the caller. The caller will update it and reinsert it back into the cache.
 385  */
 386 template <typename FACTORY>
 387 struct FindContext {
 388     FindContext(const SkMatrix* viewMatrix, const FACTORY* factory)
 389             : fViewMatrix(viewMatrix), fFactory(factory) {}
 390     const SkMatrix* const fViewMatrix;
 391     // If this is valid after Find is called then we found the vertices and they should be drawn
 392     // with fTranslate applied.
 393     sk_sp<SkVertices> fVertices;
 394     SkVector fTranslate = {0, 0};
 395
 396     // If this is valid after Find then the caller should add the vertices to the tessellation set
 397     // and create a new CachedTessellationsRec and insert it into SkResourceCache.
 398     sk_sp<CachedTessellations> fTessellationsOnFailure;
 399
 400     const FACTORY* fFactory;
 401 };
 402
 403 /**
 404  * Function called by SkResourceCache when a matching cache key is found. The FACTORY and matrix of
 405  * the FindContext are used to determine if the vertices are reusable. If so the vertices and
 406  * necessary translation vector are set on the FindContext.
 407  */
 408 template <typename FACTORY>
 409 bool FindVisitor(const SkResourceCache::Rec& baseRec, void* ctx) {
 410     FindContext<FACTORY>* findContext = (FindContext<FACTORY>*)ctx;
 411     const CachedTessellationsRec& rec = static_cast<const CachedTessellationsRec&>(baseRec);
 412     findContext->fVertices =
 413             rec.find(*findContext->fFactory, *findContext->fViewMatrix, &findContext->fTranslate);
 414     if (findContext->fVertices) {
 415         return true;
 416     }
 417     // We ref the tessellations and let the cache destroy the Rec. Once the tessellations have been
 418     // manipulated we will add a new Rec.
 419     findContext->fTessellationsOnFailure = rec.refTessellations();
 420     return false;
 421 }
 422
 423 class ShadowedPath {
 424 public:
 425     ShadowedPath(const SkPath* path, const SkMatrix* viewMatrix)
 426             : fPath(path)
 427             , fViewMatrix(viewMatrix)
 428 #if SK_SUPPORT_GPU
 429             , fShapeForKey(*path, GrStyle::SimpleFill())
 430 #endif
 431     {}
 432
 433     const SkPath& path() const { return *fPath; }
 434     const SkMatrix& viewMatrix() const { return *fViewMatrix; }
 435 #if SK_SUPPORT_GPU
 436     /** Negative means the vertices should not be cached for this path. */
 437     int keyBytes() const { return fShapeForKey.unstyledKeySize() * sizeof(uint32_t); }
 438     void writeKey(void* key) const {
 439         fShapeForKey.writeUnstyledKey(reinterpret_cast<uint32_t*>(key));
 440     }
 441     bool isRRect(SkRRect* rrect) { return fShapeForKey.asRRect(rrect, nullptr, nullptr, nullptr); }
 442 #else
 443     int keyBytes() const { return -1; }
 444     void writeKey(void* key) const { SK_ABORT("Should never be called"); }
 445     bool isRRect(SkRRect* rrect) { return false; }
 446 #endif
 447
 448 private:
 449     const SkPath* fPath;
 450     const SkMatrix* fViewMatrix;
 451 #if SK_SUPPORT_GPU
 452     GrStyledShape fShapeForKey;
 453 #endif
 454 };
 455
 456 // This creates a domain of keys in SkResourceCache used by this file.
 457 static void* kNamespace;
 458
 459 // When the SkPathRef genID changes, invalidate a corresponding GrResource described by key.
 460 class ShadowInvalidator : public SkIDChangeListener {
 461 public:
 462     ShadowInvalidator(const SkResourceCache::Key& key) {
 463         fKey.reset(new uint8_t[key.size()]);
 464         memcpy(fKey.get(), &key, key.size());
 465     }
 466
 467 private:
 468     const SkResourceCache::Key& getKey() const {
 469         return *reinterpret_cast<SkResourceCache::Key*>(fKey.get());
 470     }
 471
 472     // always purge
 473     static bool FindVisitor(const SkResourceCache::Rec&, void*) {
 474         return false;
 475     }
 476
 477     void changed() override {
 478         SkResourceCache::Find(this->getKey(), ShadowInvalidator::FindVisitor, nullptr);
 479     }
 480
 481     std::unique_ptr<uint8_t[]> fKey;
 482 };
 483
 484 /**
 485  * Draws a shadow to 'canvas'. The vertices used to draw the shadow are created by 'factory' unless
 486  * they are first found in SkResourceCache.
 487  */
 488 template <typename FACTORY>
 489 bool draw_shadow(const FACTORY& factory,
 490                  std::function<void(const SkVertices*, SkBlendMode, const SkPaint&,
 491                  SkScalar tx, SkScalar ty, bool)> drawProc, ShadowedPath& path, SkColor color) {
 492     FindContext<FACTORY> context(&path.viewMatrix(), &factory);
 493
 494     SkResourceCache::Key* key = nullptr;
 495     SkAutoSTArray<32 * 4, uint8_t> keyStorage;
 496     int keyDataBytes = path.keyBytes();
 497     if (keyDataBytes >= 0) {
 498         keyStorage.reset(keyDataBytes + sizeof(SkResourceCache::Key));
 499         key = new (keyStorage.begin()) SkResourceCache::Key();
 500         path.writeKey((uint32_t*)(keyStorage.begin() + sizeof(*key)));
 501         key->init(&kNamespace, resource_cache_shared_id(), keyDataBytes);
 502         SkResourceCache::Find(*key, FindVisitor<FACTORY>, &context);
 503     }
 504
 505     sk_sp<SkVertices> vertices;
 506     bool foundInCache = SkToBool(context.fVertices);
 507     if (foundInCache) {
 508         vertices = std::move(context.fVertices);
 509     } else {
 510         // TODO: handle transforming the path as part of the tessellator
 511         if (key) {
 512             // Update or initialize a tessellation set and add it to the cache.
 513             sk_sp<CachedTessellations> tessellations;
 514             if (context.fTessellationsOnFailure) {
 515                 tessellations = std::move(context.fTessellationsOnFailure);
 516             } else {
 517                 tessellations.reset(new CachedTessellations());
 518             }
 519             vertices = tessellations->add(path.path(), factory, path.viewMatrix(),
 520                                           &context.fTranslate);
 521             if (!vertices) {
 522                 return false;
 523             }
 524             auto rec = new CachedTessellationsRec(*key, std::move(tessellations));
 525             SkPathPriv::AddGenIDChangeListener(path.path(), sk_make_sp<ShadowInvalidator>(*key));
 526             SkResourceCache::Add(rec);
 527         } else {
 528             vertices = factory.makeVertices(path.path(), path.viewMatrix(),
 529                                             &context.fTranslate);
 530             if (!vertices) {
 531                 return false;
 532             }
 533         }
 534     }
 535
 536     SkPaint paint;
 537     // Run the vertex color through a GaussianColorFilter and then modulate the grayscale result of
 538     // that against our 'color' param.
 539     paint.setColorFilter(
 540          SkColorFilters::Blend(color, SkBlendMode::kModulate)->makeComposed(
 541                                                                 SkColorFilterPriv::MakeGaussian()));
 542
 543     drawProc(vertices.get(), SkBlendMode::kModulate, paint,
 544              context.fTranslate.fX, context.fTranslate.fY, path.viewMatrix().hasPerspective());
 545
 546     return true;
 547 }
 548 }  // namespace
 549
 550 static bool tilted(const SkPoint3& zPlaneParams) {
 551     return !SkScalarNearlyZero(zPlaneParams.fX) || !SkScalarNearlyZero(zPlaneParams.fY);
 552 }
 553
 554 void SkShadowUtils::ComputeTonalColors(SkColor inAmbientColor, SkColor inSpotColor,
 555                                        SkColor* outAmbientColor, SkColor* outSpotColor) {
 556     // For tonal color we only compute color values for the spot shadow.
 557     // The ambient shadow is greyscale only.
 558
 559     // Ambient
 560     *outAmbientColor = SkColorSetARGB(SkColorGetA(inAmbientColor), 0, 0, 0);
 561
 562     // Spot
 563     int spotR = SkColorGetR(inSpotColor);
 564     int spotG = SkColorGetG(inSpotColor);
 565     int spotB = SkColorGetB(inSpotColor);
 566     int max = std::max(std::max(spotR, spotG), spotB);
 567     int min = std::min(std::min(spotR, spotG), spotB);
 568     SkScalar luminance = 0.5f*(max + min)/255.f;
 569     SkScalar origA = SkColorGetA(inSpotColor)/255.f;
 570
 571     // We compute a color alpha value based on the luminance of the color, scaled by an
 572     // adjusted alpha value. We want the following properties to match the UX examples
 573     // (assuming a = 0.25) and to ensure that we have reasonable results when the color
 574     // is black and/or the alpha is 0:
 575     //     f(0, a) = 0
 576     //     f(luminance, 0) = 0
 577     //     f(1, 0.25) = .5
 578     //     f(0.5, 0.25) = .4
 579     //     f(1, 1) = 1
 580     // The following functions match this as closely as possible.
 581     SkScalar alphaAdjust = (2.6f + (-2.66667f + 1.06667f*origA)*origA)*origA;
 582     SkScalar colorAlpha = (3.544762f + (-4.891428f + 2.3466f*luminance)*luminance)*luminance;
 583     colorAlpha = SkTPin(alphaAdjust*colorAlpha, 0.0f, 1.0f);
 584
 585     // Similarly, we set the greyscale alpha based on luminance and alpha so that
 586     //     f(0, a) = a
 587     //     f(luminance, 0) = 0
 588     //     f(1, 0.25) = 0.15
 589     SkScalar greyscaleAlpha = SkTPin(origA*(1 - 0.4f*luminance), 0.0f, 1.0f);
 590
 591     // The final color we want to emulate is generated by rendering a color shadow (C_rgb) using an
 592     // alpha computed from the color's luminance (C_a), and then a black shadow with alpha (S_a)
 593     // which is an adjusted value of 'a'.  Assuming SrcOver, a background color of B_rgb, and
 594     // ignoring edge falloff, this becomes
 595     //
 596     //      (C_a - S_a*C_a)*C_rgb + (1 - (S_a + C_a - S_a*C_a))*B_rgb
 597     //
 598     // Assuming premultiplied alpha, this means we scale the color by (C_a - S_a*C_a) and
 599     // set the alpha to (S_a + C_a - S_a*C_a).
 600     SkScalar colorScale = colorAlpha*(SK_Scalar1 - greyscaleAlpha);
 601     SkScalar tonalAlpha = colorScale + greyscaleAlpha;
 602     SkScalar unPremulScale = colorScale / tonalAlpha;
 603     *outSpotColor = SkColorSetARGB(tonalAlpha*255.999f,
 604                                    unPremulScale*spotR,
 605                                    unPremulScale*spotG,
 606                                    unPremulScale*spotB);
 607 }
 608
 609 static bool fill_shadow_rec(const SkPath& path, const SkPoint3& zPlaneParams,
 610                             const SkPoint3& lightPos, SkScalar lightRadius,
 611                             SkColor ambientColor, SkColor spotColor,
 612                             uint32_t flags, const SkMatrix& ctm, SkDrawShadowRec* rec) {
 613     SkPoint pt = { lightPos.fX, lightPos.fY };
 614     if (!SkToBool(flags & kDirectionalLight_ShadowFlag)) {
 615         // If light position is in device space, need to transform to local space
 616         // before applying to SkCanvas.
 617         SkMatrix inverse;
 618         if (!ctm.invert(&inverse)) {
 619             return false;
 620         }
 621         inverse.mapPoints(&pt, 1);
 622     }
 623
 624     rec->fZPlaneParams   = zPlaneParams;
 625     rec->fLightPos       = { pt.fX, pt.fY, lightPos.fZ };
 626     rec->fLightRadius    = lightRadius;
 627     rec->fAmbientColor   = ambientColor;
 628     rec->fSpotColor      = spotColor;
 629     rec->fFlags          = flags;
 630
 631     return true;
 632 }
 633
 634 // Draw an offset spot shadow and outlining ambient shadow for the given path.
 635 void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, const SkPoint3& zPlaneParams,
 636                                const SkPoint3& lightPos, SkScalar lightRadius,
 637                                SkColor ambientColor, SkColor spotColor,
 638                                uint32_t flags) {
 639     SkDrawShadowRec rec;
 640     if (!fill_shadow_rec(path, zPlaneParams, lightPos, lightRadius, ambientColor, spotColor,
 641                          flags, canvas->getTotalMatrix(), &rec)) {
 642         return;
 643     }
 644
 645     canvas->private_draw_shadow_rec(path, rec);
 646 }
 647
 648 bool SkShadowUtils::GetLocalBounds(const SkMatrix& ctm, const SkPath& path,
 649                                    const SkPoint3& zPlaneParams, const SkPoint3& lightPos,
 650                                    SkScalar lightRadius, uint32_t flags, SkRect* bounds) {
 651     SkDrawShadowRec rec;
 652     if (!fill_shadow_rec(path, zPlaneParams, lightPos, lightRadius, SK_ColorBLACK, SK_ColorBLACK,
 653                          flags, ctm, &rec)) {
 654         return false;
 655     }
 656
 657     SkDrawShadowMetrics::GetLocalBounds(path, rec, ctm, bounds);
 658
 659     return true;
 660 }
 661
 662 //////////////////////////////////////////////////////////////////////////////////////////////
 663
 664 static bool validate_rec(const SkDrawShadowRec& rec) {
 665     return rec.fLightPos.isFinite() && rec.fZPlaneParams.isFinite() &&
 666            SkScalarIsFinite(rec.fLightRadius);
 667 }
 668
 669 void SkBaseDevice::drawShadow(const SkPath& path, const SkDrawShadowRec& rec) {
 670     auto drawVertsProc = [this](const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint,
 671                                 SkScalar tx, SkScalar ty, bool hasPerspective) {
 672         if (vertices->priv().vertexCount()) {
 673             // For perspective shadows we've already computed the shadow in world space,
 674             // and we can't translate it without changing it. Otherwise we concat the
 675             // change in translation from the cached version.
 676             SkAutoDeviceTransformRestore adr(
 677                     this,
 678                     hasPerspective ? SkMatrix::I()
 679                                    : this->localToDevice() * SkMatrix::Translate(tx, ty));
 680             // The vertex colors for a tesselated shadow polygon are always either opaque black
 681             // or transparent and their real contribution to the final blended color is via
 682             // their alpha. We can skip expensive per-vertex color conversion for this.
 683             this->drawVertices(vertices, SkBlender::Mode(mode), paint, /*skipColorXform=*/true);
 684         }
 685     };
 686
 687     if (!validate_rec(rec)) {
 688         return;
 689     }
 690
 691     SkMatrix viewMatrix = this->localToDevice();
 692     SkAutoDeviceTransformRestore adr(this, SkMatrix::I());
 693
 694     ShadowedPath shadowedPath(&path, &viewMatrix);
 695
 696     bool tiltZPlane = tilted(rec.fZPlaneParams);
 697     bool transparent = SkToBool(rec.fFlags & SkShadowFlags::kTransparentOccluder_ShadowFlag);
 698     bool directional = SkToBool(rec.fFlags & SkShadowFlags::kDirectionalLight_ShadowFlag);
 699     bool useBlur = SkToBool(rec.fFlags & SkShadowFlags::kConcaveBlurOnly_ShadowFlag) &&
 700                    !path.isConvex();
 701     bool uncached = tiltZPlane || path.isVolatile();
 702
 703     SkPoint3 zPlaneParams = rec.fZPlaneParams;
 704     SkPoint3 devLightPos = rec.fLightPos;
 705     if (!directional) {
 706         viewMatrix.mapPoints((SkPoint*)&devLightPos.fX, 1);
 707     }
 708     float lightRadius = rec.fLightRadius;
 709
 710     if (SkColorGetA(rec.fAmbientColor) > 0) {
 711         bool success = false;
 712         if (uncached && !useBlur) {
 713             sk_sp<SkVertices> vertices = SkShadowTessellator::MakeAmbient(path, viewMatrix,
 714                                                                           zPlaneParams,
 715                                                                           transparent);
 716             if (vertices) {
 717                 SkPaint paint;
 718                 // Run the vertex color through a GaussianColorFilter and then modulate the
 719                 // grayscale result of that against our 'color' param.
 720                 paint.setColorFilter(
 721                     SkColorFilters::Blend(rec.fAmbientColor,
 722                                                   SkBlendMode::kModulate)->makeComposed(
 723                                                                SkColorFilterPriv::MakeGaussian()));
 724                 // The vertex colors for a tesselated shadow polygon are always either opaque black
 725                 // or transparent and their real contribution to the final blended color is via
 726                 // their alpha. We can skip expensive per-vertex color conversion for this.
 727                 this->drawVertices(vertices.get(),
 728                                    SkBlender::Mode(SkBlendMode::kModulate),
 729                                    paint,
 730                                    /*skipColorXform=*/true);
 731                 success = true;
 732             }
 733         }
 734
 735         if (!success && !useBlur) {
 736             AmbientVerticesFactory factory;
 737             factory.fOccluderHeight = zPlaneParams.fZ;
 738             factory.fTransparent = transparent;
 739             if (viewMatrix.hasPerspective()) {
 740                 factory.fOffset.set(0, 0);
 741             } else {
 742                 factory.fOffset.fX = viewMatrix.getTranslateX();
 743                 factory.fOffset.fY = viewMatrix.getTranslateY();
 744             }
 745
 746             success = draw_shadow(factory, drawVertsProc, shadowedPath, rec.fAmbientColor);
 747         }
 748
 749         // All else has failed, draw with blur
 750         if (!success) {
 751             // Pretransform the path to avoid transforming the stroke, below.
 752             SkPath devSpacePath;
 753             path.transform(viewMatrix, &devSpacePath);
 754             devSpacePath.setIsVolatile(true);
 755
 756             // The tesselator outsets by AmbientBlurRadius (or 'r') to get the outer ring of
 757             // the tesselation, and sets the alpha on the path to 1/AmbientRecipAlpha (or 'a').
 758             //
 759             // We want to emulate this with a blur. The full blur width (2*blurRadius or 'f')
 760             // can be calculated by interpolating:
 761             //
 762             //            original edge        outer edge
 763             //         |       |<---------- r ------>|
 764             //         |<------|--- f -------------->|
 765             //         |       |                     |
 766             //    alpha = 1  alpha = a          alpha = 0
 767             //
 768             // Taking ratios, f/1 = r/a, so f = r/a and blurRadius = f/2.
 769             //
 770             // We now need to outset the path to place the new edge in the center of the
 771             // blur region:
 772             //
 773             //             original   new
 774             //         |       |<------|--- r ------>|
 775             //         |<------|--- f -|------------>|
 776             //         |       |<- o ->|<--- f/2 --->|
 777             //
 778             //     r = o + f/2, so o = r - f/2
 779             //
 780             // We outset by using the stroker, so the strokeWidth is o/2.
 781             //
 782             SkScalar devSpaceOutset = SkDrawShadowMetrics::AmbientBlurRadius(zPlaneParams.fZ);
 783             SkScalar oneOverA = SkDrawShadowMetrics::AmbientRecipAlpha(zPlaneParams.fZ);
 784             SkScalar blurRadius = 0.5f*devSpaceOutset*oneOverA;
 785             SkScalar strokeWidth = 0.5f*(devSpaceOutset - blurRadius);
 786
 787             // Now draw with blur
 788             SkPaint paint;
 789             paint.setColor(rec.fAmbientColor);
 790             paint.setStrokeWidth(strokeWidth);
 791             paint.setStyle(SkPaint::kStrokeAndFill_Style);
 792             SkScalar sigma = SkBlurMask::ConvertRadiusToSigma(blurRadius);
 793             bool respectCTM = false;
 794             paint.setMaskFilter(SkMaskFilter::MakeBlur(kNormal_SkBlurStyle, sigma, respectCTM));
 795             this->drawPath(devSpacePath, paint);
 796         }
 797     }
 798
 799     if (SkColorGetA(rec.fSpotColor) > 0) {
 800         bool success = false;
 801         if (uncached && !useBlur) {
 802             sk_sp<SkVertices> vertices = SkShadowTessellator::MakeSpot(path, viewMatrix,
 803                                                                        zPlaneParams,
 804                                                                        devLightPos, lightRadius,
 805                                                                        transparent,
 806                                                                        directional);
 807             if (vertices) {
 808                 SkPaint paint;
 809                 // Run the vertex color through a GaussianColorFilter and then modulate the
 810                 // grayscale result of that against our 'color' param.
 811                 paint.setColorFilter(
 812                     SkColorFilters::Blend(rec.fSpotColor,
 813                                                   SkBlendMode::kModulate)->makeComposed(
 814                                                       SkColorFilterPriv::MakeGaussian()));
 815                 // The vertex colors for a tesselated shadow polygon are always either opaque black
 816                 // or transparent and their real contribution to the final blended color is via
 817                 // their alpha. We can skip expensive per-vertex color conversion for this.
 818                 this->drawVertices(vertices.get(),
 819                                    SkBlender::Mode(SkBlendMode::kModulate),
 820                                    paint,
 821                                    /*skipColorXform=*/true);
 822                 success = true;
 823             }
 824         }
 825
 826         if (!success && !useBlur) {
 827             SpotVerticesFactory factory;
 828             factory.fOccluderHeight = zPlaneParams.fZ;
 829             factory.fDevLightPos = devLightPos;
 830             factory.fLightRadius = lightRadius;
 831
 832             SkPoint center = SkPoint::Make(path.getBounds().centerX(), path.getBounds().centerY());
 833             factory.fLocalCenter = center;
 834             viewMatrix.mapPoints(&center, 1);
 835             SkScalar radius, scale;
 836             if (SkToBool(rec.fFlags & kDirectionalLight_ShadowFlag)) {
 837                 SkDrawShadowMetrics::GetDirectionalParams(zPlaneParams.fZ, devLightPos.fX,
 838                                                           devLightPos.fY, devLightPos.fZ,
 839                                                           lightRadius, &radius, &scale,
 840                                                           &factory.fOffset);
 841             } else {
 842                 SkDrawShadowMetrics::GetSpotParams(zPlaneParams.fZ, devLightPos.fX - center.fX,
 843                                                    devLightPos.fY - center.fY, devLightPos.fZ,
 844                                                    lightRadius, &radius, &scale, &factory.fOffset);
 845             }
 846
 847             SkRect devBounds;
 848             viewMatrix.mapRect(&devBounds, path.getBounds());
 849             if (transparent ||
 850                 SkTAbs(factory.fOffset.fX) > 0.5f*devBounds.width() ||
 851                 SkTAbs(factory.fOffset.fY) > 0.5f*devBounds.height()) {
 852                 // if the translation of the shadow is big enough we're going to end up
 853                 // filling the entire umbra, we can treat these as all the same
 854                 if (directional) {
 855                     factory.fOccluderType =
 856                             SpotVerticesFactory::OccluderType::kDirectionalTransparent;
 857                 } else {
 858                     factory.fOccluderType = SpotVerticesFactory::OccluderType::kPointTransparent;
 859                 }
 860             } else if (directional) {
 861                 factory.fOccluderType = SpotVerticesFactory::OccluderType::kDirectional;
 862             } else if (factory.fOffset.length()*scale + scale < radius) {
 863                 // if we don't translate more than the blur distance, can assume umbra is covered
 864                 factory.fOccluderType = SpotVerticesFactory::OccluderType::kPointOpaqueNoUmbra;
 865             } else if (path.isConvex()) {
 866                 factory.fOccluderType = SpotVerticesFactory::OccluderType::kPointOpaquePartialUmbra;
 867             } else {
 868                 factory.fOccluderType = SpotVerticesFactory::OccluderType::kPointTransparent;
 869             }
 870             // need to add this after we classify the shadow
 871             factory.fOffset.fX += viewMatrix.getTranslateX();
 872             factory.fOffset.fY += viewMatrix.getTranslateY();
 873
 874             SkColor color = rec.fSpotColor;
 875 #ifdef DEBUG_SHADOW_CHECKS
 876             switch (factory.fOccluderType) {
 877                 case SpotVerticesFactory::OccluderType::kPointTransparent:
 878                     color = 0xFFD2B48C;  // tan for transparent
 879                     break;
 880                 case SpotVerticesFactory::OccluderType::kPointOpaquePartialUmbra:
 881                     color = 0xFFFFA500;   // orange for opaque
 882                     break;
 883                 case SpotVerticesFactory::OccluderType::kPointOpaqueNoUmbra:
 884                     color = 0xFFE5E500;  // corn yellow for covered
 885                     break;
 886                 case SpotVerticesFactory::OccluderType::kDirectional:
 887                 case SpotVerticesFactory::OccluderType::kDirectionalTransparent:
 888                     color = 0xFF550000;  // dark red for directional
 889                     break;
 890             }
 891 #endif
 892             success = draw_shadow(factory, drawVertsProc, shadowedPath, color);
 893         }
 894
 895         // All else has failed, draw with blur
 896         if (!success) {
 897             SkMatrix shadowMatrix;
 898             SkScalar radius;
 899             if (!SkDrawShadowMetrics::GetSpotShadowTransform(devLightPos, lightRadius,
 900                                                              viewMatrix, zPlaneParams,
 901                                                              path.getBounds(), directional,
 902                                                              &shadowMatrix, &radius)) {
 903                 return;
 904             }
 905             SkAutoDeviceTransformRestore adr2(this, shadowMatrix);
 906
 907             SkPaint paint;
 908             paint.setColor(rec.fSpotColor);
 909             SkScalar sigma = SkBlurMask::ConvertRadiusToSigma(radius);
 910             bool respectCTM = false;
 911             paint.setMaskFilter(SkMaskFilter::MakeBlur(kNormal_SkBlurStyle, sigma, respectCTM));
 912             this->drawPath(path, paint);
 913         }
 914     }
 915 }