aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/core/SkClipStack.cpp
blob: 52b12cf7795639aa773c8427dc7525c3c59493d6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "SkClipStack.h"
#include "SkPath.h"
#include "SkThread.h"

#include <new>


// 0-2 are reserved for invalid, empty & wide-open
int32_t SkClipStack::gGenID = 3; 

struct SkClipStack::Rec {
    enum State {
        kEmpty_State,
        kRect_State,
        kPath_State
    };

    SkPath          fPath;
    SkRect          fRect;
    int             fSaveCount;
    SkRegion::Op    fOp;
    State           fState;
    bool            fDoAA;

    // fFiniteBoundType and fFiniteBound are used to incrementally update
    // the clip stack's bound. When fFiniteBoundType is kNormal_BoundsType, 
    // fFiniteBound represents the  conservative bounding box of the pixels 
    // that aren't clipped (i.e., any pixels that can be drawn to are inside 
    // the bound). When fFiniteBoundType is kInsideOut_BoundsType (which occurs 
    // when a clip is inverse filled), fFiniteBound represents the 
    // conservative bounding box of the pixels that _are_ clipped (i.e., any 
    // pixels that cannot be drawn to are inside the bound). When 
    // fFiniteBoundType is kInsideOut_BoundsType the actual bound is
    // the infinite plane. This behavior of fFiniteBoundType and
    // fFiniteBound is required so that we can capture the cancelling out
    // of the extensions to infinity when two inverse filled clips are
    // Booleaned together.
    SkClipStack::BoundsType fFiniteBoundType;
    SkRect                  fFiniteBound;
    bool                    fIsIntersectionOfRects;

    int                     fGenID;

    Rec(int saveCount, const SkRect& rect, SkRegion::Op op, bool doAA) 
        : fRect(rect)
        , fGenID(kInvalidGenID) {
        fSaveCount = saveCount;
        fOp = op;
        fState = kRect_State;
        fDoAA = doAA;
        // bounding box members are updated in a following updateBound call
    }

    Rec(int saveCount, const SkPath& path, SkRegion::Op op, bool doAA) 
        : fPath(path)
        , fGenID(kInvalidGenID) {
        fRect.setEmpty();
        fSaveCount = saveCount;
        fOp = op;
        fState = kPath_State;
        fDoAA = doAA;
        // bounding box members are updated in a following updateBound call
    }

    void setEmpty() {
        fState = kEmpty_State;
        fFiniteBound.setEmpty();
        fFiniteBoundType = kNormal_BoundsType;
        fIsIntersectionOfRects = false;
        fGenID = kEmptyGenID;
    }

    void checkEmpty() {
        SkASSERT(fFiniteBound.isEmpty());
        SkASSERT(kNormal_BoundsType == fFiniteBoundType);
        SkASSERT(!fIsIntersectionOfRects);
        SkASSERT(kEmptyGenID == fGenID);
    }

    bool operator==(const Rec& b) const {
        if (fSaveCount != b.fSaveCount || 
            fGenID != b.fGenID ||
            fOp != b.fOp || 
            fState != b.fState ||
            fDoAA != b.fDoAA) {
            return false;
        }
        switch (fState) {
            case kEmpty_State:
                return true;
            case kRect_State:
                return fRect == b.fRect;
            case kPath_State:
                return fPath == b.fPath;
        }
        return false;  // Silence the compiler.
    }

    bool operator!=(const Rec& b) const {
        return !(*this == b);
    }


    /**
     *  Returns true if this Rec can be intersected in place with a new clip
     */
    bool canBeIntersectedInPlace(int saveCount, SkRegion::Op op) const {
        if (kEmpty_State == fState && (
                    SkRegion::kDifference_Op == op ||
                    SkRegion::kIntersect_Op == op)) {
            return true;
        }
        // Only clips within the same save/restore frame (as captured by
        // the save count) can be merged
        return  fSaveCount == saveCount && 
                SkRegion::kIntersect_Op == op &&
                (SkRegion::kIntersect_Op == fOp || SkRegion::kReplace_Op == fOp);
    }

    /**
     * This method checks to see if two rect clips can be safely merged into
     * one. The issue here is that to be strictly correct all the edges of
     * the resulting rect must have the same anti-aliasing.
     */
    bool rectRectIntersectAllowed(const SkRect& newR, bool newAA) const {
        SkASSERT(kRect_State == fState);

        if (fDoAA == newAA) {
            // if the AA setting is the same there is no issue
            return true;
        }

        if (!SkRect::Intersects(fRect, newR)) {
            // The calling code will correctly set the result to the empty clip
            return true;
        }

        if (fRect.contains(newR)) {
            // if the new rect carves out a portion of the old one there is no
            // issue
            return true;
        }

        // So either the two overlap in some complex manner or newR contains oldR.
        // In the first, case the edges will require different AA. In the second,
        // the AA setting that would be carried forward is incorrect (e.g., oldR 
        // is AA while newR is BW but since newR contains oldR, oldR will be 
        // drawn BW) since the new AA setting will predominate.
        return false;
    }


    /**
     * The different combination of fill & inverse fill when combining
     * bounding boxes
     */ 
    enum FillCombo {
        kPrev_Cur_FillCombo,
        kPrev_InvCur_FillCombo,
        kInvPrev_Cur_FillCombo,
        kInvPrev_InvCur_FillCombo
    };

    // a mirror of CombineBoundsRevDiff
    void CombineBoundsDiff(FillCombo combination, const SkRect& prevFinite) {
        switch (combination) {
            case kInvPrev_InvCur_FillCombo:
                // In this case the only pixels that can remain set
                // are inside the current clip rect since the extensions
                // to infinity of both clips cancel out and whatever
                // is outside of the current clip is removed
                fFiniteBoundType = kNormal_BoundsType;
                break;
            case kInvPrev_Cur_FillCombo:
                // In this case the current op is finite so the only pixels
                // that aren't set are whatever isn't set in the previous
                // clip and whatever this clip carves out
                fFiniteBound.join(prevFinite);
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kPrev_InvCur_FillCombo:
                // In this case everything outside of this clip's bound
                // is erased, so the only pixels that can remain set 
                // occur w/in the intersection of the two finite bounds
                if (!fFiniteBound.intersect(prevFinite)) {
                    fFiniteBound.setEmpty();
                }
                fFiniteBoundType = kNormal_BoundsType;
                break;
            case kPrev_Cur_FillCombo:
                // The most conservative result bound is that of the 
                // prior clip. This could be wildly incorrect if the 
                // second clip either exactly matches the first clip 
                // (which should yield the empty set) or reduces the
                // size of the prior bound (e.g., if the second clip 
                // exactly matched the bottom half of the prior clip).
                // We ignore these two possibilities.
                fFiniteBound = prevFinite;
                break;
            default:
                SkDEBUGFAIL("SkClipStack::Rec::CombineBoundsDiff Invalid fill combination");
                break;
        }
    }

    void CombineBoundsXOR(int combination, const SkRect& prevFinite) {

        switch (combination) {
            case kInvPrev_Cur_FillCombo:       // fall through
            case kPrev_InvCur_FillCombo:
                // With only one of the clips inverted the result will always
                // extend to infinity. The only pixels that may be un-writeable
                // lie within the union of the two finite bounds
                fFiniteBound.join(prevFinite);
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kInvPrev_InvCur_FillCombo:
                // The only pixels that can survive are within the 
                // union of the two bounding boxes since the extensions
                // to infinity of both clips cancel out
                // fall through!
            case kPrev_Cur_FillCombo:
                // The most conservative bound for xor is the 
                // union of the two bounds. If the two clips exactly overlapped
                // the xor could yield the empty set. Similarly the xor 
                // could reduce the size of the original clip's bound (e.g., 
                // if the second clip exactly matched the bottom half of the 
                // first clip). We ignore these two cases.
                fFiniteBound.join(prevFinite);
                fFiniteBoundType = kNormal_BoundsType;
                break;
            default:
                SkDEBUGFAIL("SkClipStack::Rec::CombineBoundsXOR Invalid fill combination");
                break;
        }
    }

    // a mirror of CombineBoundsIntersection
    void CombineBoundsUnion(int combination, const SkRect& prevFinite) {

        switch (combination) {
            case kInvPrev_InvCur_FillCombo:
                if (!fFiniteBound.intersect(prevFinite)) {
                    fFiniteBound.setEmpty();
                }
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kInvPrev_Cur_FillCombo:
                // The only pixels that won't be drawable are inside
                // the prior clip's finite bound
                fFiniteBound = prevFinite;
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kPrev_InvCur_FillCombo:
                // The only pixels that won't be drawable are inside
                // this clip's finite bound
                break;
            case kPrev_Cur_FillCombo:
                fFiniteBound.join(prevFinite);
                break;
            default:
                SkDEBUGFAIL("SkClipStack::Rec::CombineBoundsUnion Invalid fill combination");
                break;
        }
    }

    // a mirror of CombineBoundsUnion
    void CombineBoundsIntersection(int combination, const SkRect& prevFinite) {

        switch (combination) {
            case kInvPrev_InvCur_FillCombo:
                // The only pixels that aren't writable in this case 
                // occur in the union of the two finite bounds
                fFiniteBound.join(prevFinite);
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kInvPrev_Cur_FillCombo:      
                // In this case the only pixels that will remain writeable
                // are within the current clip
                break;
            case kPrev_InvCur_FillCombo:
                // In this case the only pixels that will remain writeable
                // are with the previous clip
                fFiniteBound = prevFinite;
                fFiniteBoundType = kNormal_BoundsType;
                break;
            case kPrev_Cur_FillCombo:
                if (!fFiniteBound.intersect(prevFinite)) {
                    fFiniteBound.setEmpty();
                }
                break;
            default:
                SkDEBUGFAIL("SkClipStack::Rec::CombineBoundsIntersection Invalid fill combination");
                break;
        }
    }

    // a mirror of CombineBoundsDiff
    void CombineBoundsRevDiff(int combination, const SkRect& prevFinite) {

        switch (combination) {
            case kInvPrev_InvCur_FillCombo:
                // The only pixels that can survive are in the 
                // previous bound since the extensions to infinity in
                // both clips cancel out
                fFiniteBound = prevFinite;
                fFiniteBoundType = kNormal_BoundsType;
                break;
            case kInvPrev_Cur_FillCombo:
                if (!fFiniteBound.intersect(prevFinite)) {
                    fFiniteBound.setEmpty();
                }
                fFiniteBoundType = kNormal_BoundsType;
                break;
            case kPrev_InvCur_FillCombo:
                fFiniteBound.join(prevFinite);
                fFiniteBoundType = kInsideOut_BoundsType;
                break;
            case kPrev_Cur_FillCombo:
                // Fall through - as with the kDifference_Op case, the 
                // most conservative result bound is the bound of the
                // current clip. The prior clip could reduce the size of this 
                // bound (as in the kDifference_Op case) but we are ignoring 
                // those cases.
                break;
            default:
                SkDEBUGFAIL("SkClipStack::Rec::CombineBoundsRevDiff Invalid fill combination");
                break;
        }
    }

    void updateBound(const Rec* prior) {

        // First, optimistically update the current Rec's bound information 
        // with the current clip's bound
        fIsIntersectionOfRects = false;
        if (kRect_State == fState) {
            fFiniteBound = fRect;
            fFiniteBoundType = kNormal_BoundsType;

            if (SkRegion::kReplace_Op == fOp ||
                (SkRegion::kIntersect_Op == fOp && NULL == prior) || 
                (SkRegion::kIntersect_Op == fOp && prior->fIsIntersectionOfRects &&
                 prior->rectRectIntersectAllowed(fRect, fDoAA))) {
                fIsIntersectionOfRects = true;
            }

        } else {
            fFiniteBound = fPath.getBounds();

            if (fPath.isInverseFillType()) {
                fFiniteBoundType = kInsideOut_BoundsType;
            } else {
                fFiniteBoundType = kNormal_BoundsType;
            }
        }

        if (!fDoAA) {
            // Here we mimic a non-anti-aliased scanline system. If there is
            // no anti-aliasing we can integerize the bounding box to exclude
            // fractional parts that won't be rendered.
            // Note: the left edge is handled slightly differently below. We
            // are a bit more generous in the rounding since we don't want to
            // risk missing the left pixels when fLeft is very close to .5
            fFiniteBound.set(SkIntToScalar(SkScalarFloorToInt(fFiniteBound.fLeft+0.45f)), 
                             SkIntToScalar(SkScalarRound(fFiniteBound.fTop)), 
                             SkIntToScalar(SkScalarRound(fFiniteBound.fRight)), 
                             SkIntToScalar(SkScalarRound(fFiniteBound.fBottom)));
        }

        // Now set up the previous Rec's bound information taking into
        // account that there may be no previous clip
        SkRect prevFinite;
        SkClipStack::BoundsType prevType;

        if (NULL == prior) {
            // no prior clip means the entire plane is writable
            prevFinite.setEmpty();   // there are no pixels that cannot be drawn to
            prevType = kInsideOut_BoundsType;
        } else {
            prevFinite = prior->fFiniteBound;
            prevType = prior->fFiniteBoundType;
        }

        FillCombo combination = kPrev_Cur_FillCombo;
        if (kInsideOut_BoundsType == fFiniteBoundType) {
            combination = (FillCombo) (combination | 0x01);
        }
        if (kInsideOut_BoundsType == prevType) {
            combination = (FillCombo) (combination | 0x02);
        }

        SkASSERT(kInvPrev_InvCur_FillCombo == combination || 
                 kInvPrev_Cur_FillCombo == combination ||
                 kPrev_InvCur_FillCombo == combination || 
                 kPrev_Cur_FillCombo == combination);

        // Now integrate with clip with the prior clips
        switch (fOp) {
            case SkRegion::kDifference_Op:
                this->CombineBoundsDiff(combination, prevFinite);
                break;
            case SkRegion::kXOR_Op:
                this->CombineBoundsXOR(combination, prevFinite);
                break;
            case SkRegion::kUnion_Op:
                this->CombineBoundsUnion(combination, prevFinite);
                break;
            case SkRegion::kIntersect_Op:
                this->CombineBoundsIntersection(combination, prevFinite);
                break;
            case SkRegion::kReverseDifference_Op:
                this->CombineBoundsRevDiff(combination, prevFinite);
                break;
            case SkRegion::kReplace_Op:
                // Replace just ignores everything prior
                // The current clip's bound information is already filled in
                // so nothing to do
                break;
            default:
                SkDebugf("SkRegion::Op error/n");
                SkASSERT(0);
                break;
        }
    }
};


SkClipStack::SkClipStack() 
    : fDeque(sizeof(Rec))
    , fSaveCount(0) {
}

SkClipStack::SkClipStack(const SkClipStack& b) : fDeque(sizeof(Rec)) {
    *this = b;
}

SkClipStack::SkClipStack(const SkRect& r) 
    : fDeque(sizeof(Rec))
    , fSaveCount(0) {
    if (!r.isEmpty()) {
        this->clipDevRect(r, SkRegion::kReplace_Op, false);
    }
}

SkClipStack::SkClipStack(const SkIRect& r) 
    : fDeque(sizeof(Rec))
    , fSaveCount(0) {
    if (!r.isEmpty()) {
        SkRect temp;
        temp.set(r);
        this->clipDevRect(temp, SkRegion::kReplace_Op, false);
    }
}

SkClipStack::~SkClipStack() {
    reset();
}

SkClipStack& SkClipStack::operator=(const SkClipStack& b) {
    if (this == &b) {
        return *this;
    }
    reset();

    fSaveCount = b.fSaveCount;
    SkDeque::F2BIter recIter(b.fDeque);
    for (const Rec* rec = (const Rec*)recIter.next();
         rec != NULL;
         rec = (const Rec*)recIter.next()) {
        new (fDeque.push_back()) Rec(*rec);
    }

    return *this;
}

bool SkClipStack::operator==(const SkClipStack& b) const {
    if (fSaveCount != b.fSaveCount || 
        fDeque.count() != b.fDeque.count()) {
        return false;
    }
    SkDeque::F2BIter myIter(fDeque);
    SkDeque::F2BIter bIter(b.fDeque);
    const Rec* myRec = (const Rec*)myIter.next();
    const Rec* bRec = (const Rec*)bIter.next();

    while (myRec != NULL && bRec != NULL) {
        if (*myRec != *bRec) {
            return false;
        }
        myRec = (const Rec*)myIter.next();
        bRec = (const Rec*)bIter.next();
    }
    return myRec == NULL && bRec == NULL;
}

void SkClipStack::reset() {
    // We used a placement new for each object in fDeque, so we're responsible
    // for calling the destructor on each of them as well.
    while (!fDeque.empty()) {
        Rec* rec = (Rec*)fDeque.back();
        rec->~Rec();
        fDeque.pop_back();
    }

    fSaveCount = 0;
}

void SkClipStack::save() {
    fSaveCount += 1;
}

void SkClipStack::restore() {
    fSaveCount -= 1;
    while (!fDeque.empty()) {
        Rec* rec = (Rec*)fDeque.back();
        if (rec->fSaveCount <= fSaveCount) {
            break;
        }
        this->purgeClip(rec);
        rec->~Rec();
        fDeque.pop_back();
    }
}

void SkClipStack::getBounds(SkRect* canvFiniteBound, 
                            BoundsType* boundType,
                            bool* isIntersectionOfRects) const {
    SkASSERT(NULL != canvFiniteBound && NULL != boundType);

    Rec* rec = (Rec*)fDeque.back();

    if (NULL == rec) {
        // the clip is wide open - the infinite plane w/ no pixels un-writeable
        canvFiniteBound->setEmpty();
        *boundType = kInsideOut_BoundsType;
        if (NULL != isIntersectionOfRects) {
            *isIntersectionOfRects = false;
        }
        return;
    }

    *canvFiniteBound = rec->fFiniteBound;
    *boundType = rec->fFiniteBoundType;
    if (NULL != isIntersectionOfRects) {
        *isIntersectionOfRects = rec->fIsIntersectionOfRects;
    }
}

void SkClipStack::clipDevRect(const SkRect& rect, SkRegion::Op op, bool doAA) {

    int32_t genID = GetNextGenID();

    SkDeque::Iter iter(fDeque, SkDeque::Iter::kBack_IterStart);
    Rec* rec = (Rec*) iter.prev();

    if (rec && rec->canBeIntersectedInPlace(fSaveCount, op)) {
        switch (rec->fState) {
            case Rec::kEmpty_State:
                rec->checkEmpty();
                return;
            case Rec::kRect_State:
                if (rec->rectRectIntersectAllowed(rect, doAA)) {
                    this->purgeClip(rec);
                    if (!rec->fRect.intersect(rect)) {
                        rec->setEmpty();
                        return;
                    }

                    rec->fDoAA = doAA;
                    Rec* prev = (Rec*) iter.prev();
                    rec->updateBound(prev);
                    rec->fGenID = genID;
                    return;
                }
                break;
            case Rec::kPath_State:
                if (!SkRect::Intersects(rec->fPath.getBounds(), rect)) {
                    this->purgeClip(rec);
                    rec->setEmpty();
                    return;
                }
                break;
        }
    }
    new (fDeque.push_back()) Rec(fSaveCount, rect, op, doAA);
    ((Rec*) fDeque.back())->updateBound(rec);
    ((Rec*) fDeque.back())->fGenID = genID;

    if (rec && rec->fSaveCount == fSaveCount) {
        this->purgeClip(rec);
    }
}

void SkClipStack::clipDevPath(const SkPath& path, SkRegion::Op op, bool doAA) {
    SkRect alt;
    if (path.isRect(&alt)) {
        return this->clipDevRect(alt, op, doAA);
    }

    int32_t genID = GetNextGenID();

    Rec* rec = (Rec*)fDeque.back();
    if (rec && rec->canBeIntersectedInPlace(fSaveCount, op)) {
        const SkRect& pathBounds = path.getBounds();
        switch (rec->fState) {
            case Rec::kEmpty_State:
                rec->checkEmpty();
                return;
            case Rec::kRect_State:
                if (!SkRect::Intersects(rec->fRect, pathBounds)) {
                    this->purgeClip(rec);
                    rec->setEmpty();
                    return;
                }
                break;
            case Rec::kPath_State:
                if (!SkRect::Intersects(rec->fPath.getBounds(), pathBounds)) {
                    this->purgeClip(rec);
                    rec->setEmpty();
                    return;
                }
                break;
        }
    }
    new (fDeque.push_back()) Rec(fSaveCount, path, op, doAA);
    ((Rec*) fDeque.back())->updateBound(rec);
    ((Rec*) fDeque.back())->fGenID = genID;

    if (rec && rec->fSaveCount == fSaveCount) {
        this->purgeClip(rec);
    }
}

bool SkClipStack::isWideOpen() const { 
    if (0 == fDeque.count()) {
        return true;
    }
    
    const Rec* back = (const Rec*) fDeque.back();
    return kInsideOut_BoundsType == back->fFiniteBoundType &&
           back->fFiniteBound.isEmpty();
}

///////////////////////////////////////////////////////////////////////////////

SkClipStack::Iter::Iter() : fStack(NULL) {
}

bool operator==(const SkClipStack::Iter::Clip& a,
                const SkClipStack::Iter::Clip& b) {
    return a.fOp == b.fOp && a.fDoAA == b.fDoAA &&
           ((a.fRect == NULL && b.fRect == NULL) ||
               (a.fRect != NULL && b.fRect != NULL && *a.fRect == *b.fRect)) &&
           ((a.fPath == NULL && b.fPath == NULL) ||
               (a.fPath != NULL && b.fPath != NULL && *a.fPath == *b.fPath));
}

bool operator!=(const SkClipStack::Iter::Clip& a,
                const SkClipStack::Iter::Clip& b) {
    return !(a == b);
}

SkClipStack::Iter::Iter(const SkClipStack& stack, IterStart startLoc)
    : fStack(&stack) {
    this->reset(stack, startLoc);
}

const SkClipStack::Iter::Clip* SkClipStack::Iter::updateClip(
                        const SkClipStack::Rec* rec) {
    switch (rec->fState) {
        case SkClipStack::Rec::kEmpty_State:
            fClip.fRect = NULL;
            fClip.fPath = NULL;
            break;
        case SkClipStack::Rec::kRect_State:
            fClip.fRect = &rec->fRect;
            fClip.fPath = NULL;
            break;
        case SkClipStack::Rec::kPath_State:
            fClip.fRect = NULL;
            fClip.fPath = &rec->fPath;
            break;
    }
    fClip.fOp = rec->fOp;
    fClip.fDoAA = rec->fDoAA;
    return &fClip;
}

const SkClipStack::Iter::Clip* SkClipStack::Iter::next() {
    const SkClipStack::Rec* rec = (const SkClipStack::Rec*)fIter.next();
    if (NULL == rec) {
        return NULL;
    }

    return this->updateClip(rec);
}

const SkClipStack::Iter::Clip* SkClipStack::Iter::prev() {
    const SkClipStack::Rec* rec = (const SkClipStack::Rec*)fIter.prev();
    if (NULL == rec) {
        return NULL;
    }

    return this->updateClip(rec);
}

const SkClipStack::Iter::Clip* SkClipStack::Iter::skipToTopmost(SkRegion::Op op) {

    if (NULL == fStack) {
        return NULL;
    }

    fIter.reset(fStack->fDeque, SkDeque::Iter::kBack_IterStart);

    const SkClipStack::Rec* rec = NULL;

    for (rec = (const SkClipStack::Rec*) fIter.prev();
         NULL != rec;
         rec = (const SkClipStack::Rec*) fIter.prev()) {

        if (op == rec->fOp) {
            // The Deque's iterator is actually one pace ahead of the
            // returned value. So while "rec" is the element we want to 
            // return, the iterator is actually pointing at (and will
            // return on the next "next" or "prev" call) the element
            // in front of it in the deque. Bump the iterator forward a 
            // step so we get the expected result.
            if (NULL == fIter.next()) {
                // The reverse iterator has run off the front of the deque
                // (i.e., the "op" clip is the first clip) and can't
                // recover. Reset the iterator to start at the front.
                fIter.reset(fStack->fDeque, SkDeque::Iter::kFront_IterStart);
            }
            break;
        }
    }

    if (NULL == rec) {
        // There were no "op" clips
        fIter.reset(fStack->fDeque, SkDeque::Iter::kFront_IterStart);
    }

    return this->next();
}

void SkClipStack::Iter::reset(const SkClipStack& stack, IterStart startLoc) {
    fStack = &stack;
    fIter.reset(stack.fDeque, static_cast<SkDeque::Iter::IterStart>(startLoc));
}

// helper method
void SkClipStack::getConservativeBounds(int offsetX,
                                        int offsetY,
                                        int maxWidth,
                                        int maxHeight,
                                        SkRect* devBounds,
                                        bool* isIntersectionOfRects) const {
    SkASSERT(NULL != devBounds);

    devBounds->setLTRB(0, 0, 
                       SkIntToScalar(maxWidth), SkIntToScalar(maxHeight));

    SkRect temp;
    SkClipStack::BoundsType boundType;
    
    // temp starts off in canvas space here
    this->getBounds(&temp, &boundType, isIntersectionOfRects);
    if (SkClipStack::kInsideOut_BoundsType == boundType) {
        return;
    }

    // but is converted to device space here
    temp.offset(SkIntToScalar(offsetX), SkIntToScalar(offsetY));

    if (!devBounds->intersect(temp)) {
        devBounds->setEmpty();
    }
}

void SkClipStack::addPurgeClipCallback(PFPurgeClipCB callback, void* data) const {
    ClipCallbackData temp = { callback, data };
    fCallbackData.append(1, &temp);
}

void SkClipStack::removePurgeClipCallback(PFPurgeClipCB callback, void* data) const {
    ClipCallbackData temp = { callback, data };
    int index = fCallbackData.find(temp);
    if (index >= 0) {
        fCallbackData.removeShuffle(index);
    }
}

// The clip state represented by 'rec' will never be used again. Purge it.
void SkClipStack::purgeClip(Rec* rec) {
    SkASSERT(NULL != rec);

    for (int i = 0; i < fCallbackData.count(); ++i) {
        (*fCallbackData[i].fCallback)(rec->fGenID, fCallbackData[i].fData);
    }

    // Invalidate rec's gen ID so handlers can detect already handled records
    rec->fGenID = kInvalidGenID;
}

int32_t SkClipStack::GetNextGenID() {
    return sk_atomic_inc(&gGenID);
}