src/gpu/graphite/ClipStack_graphite.h - skia - Git at Google

 /*
  * Copyright 2022 Google LLC
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #ifndef skgpu_graphite_ClipStack_DEFINED
 #define skgpu_graphite_ClipStack_DEFINED

 #include "include/core/SkClipOp.h"
 #include "src/core/SkTBlockList.h"
 #include "src/gpu/graphite/DrawOrder.h"
 #include "src/gpu/graphite/geom/Shape.h"
 #include "src/gpu/graphite/geom/Transform_graphite.h"

 class SkShader;
 class SkStrokeRec;

 namespace skgpu::graphite {

 class BoundsManager;
 class Clip;
 class Device;
 class Geometry;

 // TODO: Port over many of the unit tests for skgpu/v1/ClipStack defined in GrClipStackTest since
 // those tests do a thorough job of enumerating the different element combinations.
 class ClipStack {
 public:
     // TODO: Some of these states reflect what SkDevice requires. Others are based on what Ganesh
     // could handle analytically. They will likely change as graphite's clips are sorted out
     enum class ClipState : uint8_t {
         kEmpty, kWideOpen, kDeviceRect, kDeviceRRect, kComplex
     };

     // All data describing a geometric modification to the clip
     struct Element {
         Shape     fShape;
         Transform fLocalToDevice; // TODO: reference a cached Transform like DrawList?
         SkClipOp  fOp;
     };

     // 'owningDevice' must outlive the clip stack.
     ClipStack(Device* owningDevice);

     ~ClipStack();

     ClipStack(const ClipStack&) = delete;
     ClipStack& operator=(const ClipStack&) = delete;

     ClipState clipState() const { return this->currentSaveRecord().state(); }
     int maxDeferredClipDraws() const { return fElements.count(); }
     Rect conservativeBounds() const;

     class ElementIter;
     // Provides for-range over active, valid clip elements from most recent to oldest.
     // The iterator provides items as "const Element&".
     inline ElementIter begin() const;
     inline ElementIter end() const;

     // Clip stack manipulation
     void save();
     void restore();

     void clipShape(const Transform& localToDevice, const Shape& shape, SkClipOp op);
     void clipShader(sk_sp<SkShader> shader);

     // Apply the clip stack to the draw described by the provided transform, shape, and stroke.
     // The provided 'z' value is the depth value that the draw will use if it's not clipped out
     // entirely. Applying clips to a draw is a mostly lazy operation except for what is returned:
     //  - The Clip's scissor is set to 'conservativeBounds()'.
     //  - The Clip stores the draw's clipped bounds, taking into account its transform, styling, and
     //    the above scissor.
     //  - The CompressedPaintersOrder is the largest order that will be used by any of the clip
     //    elements that affect the draw.
     //
     // In addition to computing these values, the clip stack updates per-clip element state for
     // later rendering. Clip shapes that affect draws are later recorded into the Device's
     // DrawContext with their own painter's order chosen to sort earlier than all affected draws
     // but using a Z value greater than affected draws. This ensures that the draws fail the depth
     // test for clipped-out pixels.
     //
     // If the draw is clipped out, the returned draw bounds will be empty.
     std::pair<Clip, CompressedPaintersOrder> applyClipToDraw(const BoundsManager*,
                                                              const Transform&,
                                                              const Geometry&,
                                                              const SkStrokeRec&,
                                                              PaintersDepth z);

     void recordDeferredClipDraws();

 private:
     // SaveRecords and Elements are stored in two parallel stacks. The top-most SaveRecord is the
     // active record, older records represent earlier save points and aren't modified until they
     // become active again. Elements may be owned by the active SaveRecord, in which case they are
     // fully mutable, or they may be owned by a prior SaveRecord. However, Elements from both the
     // active SaveRecord and older records can be valid and affect draw operations. Elements are
     // marked inactive when new elements are determined to supersede their effect completely.
     // Inactive elements of the active SaveRecord can be deleted immediately; inactive elements of
     // older SaveRecords may become active again as the save stack is popped back.
     //
     // See go/grclipstack-2.0 for additional details and visualization of the data structures.
     class SaveRecord;

     // Internally, a lot of clip reasoning is based on an op, outer bounds, and whether a shape
     // contains another (possibly just conservatively based on inner/outer device-space bounds).
     // Element and SaveRecord store this information directly. A draw is equivalent to a clip
     // element with the intersection op. TransformedShape is a lightweight wrapper that can convert
     // these different types into a common type that Simplify() can reason about.
     struct TransformedShape;
     // This captures which of the two elements in (A op B) would be required when they are combined,
     // where op is intersect or difference.
     enum class SimplifyResult {
         kEmpty,
         kAOnly,
         kBOnly,
         kBoth
     };
     static SimplifyResult Simplify(const TransformedShape& a, const TransformedShape& b);

     // Wraps the geometric Element data with logic for containment and bounds testing.
     class RawElement : private Element {
     public:
         using Stack = SkTBlockList<RawElement, 1>;

         RawElement(const Rect& deviceBounds,
                    const Transform& localToDevice,
                    const Shape& shape,
                    SkClipOp op);

         ~RawElement() {
             // A pending draw means the element affects something already recorded, so its own
             // shape needs to be recorded as a draw. Since recording requires the Device (and
             // DrawContext), it must happen before we destroy the element itself.
             SkASSERT(!this->hasPendingDraw());
         }

         // Silence warnings about implicit copy ctor/assignment because we're declaring a dtor
         RawElement(const RawElement&) = default;
         RawElement& operator=(const RawElement&) = default;

         operator TransformedShape() const;

         const Element& asElement()      const { return *this;                                }
         bool           hasPendingDraw() const { return fOrder != DrawOrder::kNoIntersection; }

         const Shape&     shape()         const { return fShape;         }
         const Transform& localToDevice() const { return fLocalToDevice; }
         const Rect&      outerBounds()   const { return fOuterBounds;   }
         const Rect&      innerBounds()   const { return fInnerBounds;   }
         SkClipOp         op()            const { return fOp;            }
         ClipState        clipType()      const;

         // As new elements are pushed on to the stack, they may make older elements redundant.
         // The old elements are marked invalid so they are skipped during clip application, but may
         // become active again when a save record is restored.
         bool isInvalid() const { return fInvalidatedByIndex >= 0; }
         void markInvalid(const SaveRecord& current);
         void restoreValid(const SaveRecord& current);

         // 'added' represents a new op added to the element stack. Its combination with this element
         // can result in a number of possibilities:
         //  1. The entire clip is empty (signaled by both this and 'added' being invalidated).
         //  2. The 'added' op supercedes this element (this element is invalidated).
         //  3. This op supercedes the 'added' element (the added element is marked invalidated).
         //  4. Their combination can be represented by a single new op (in which case this
         //     element should be invalidated, and the combined shape stored in 'added').
         //  5. Or both elements remain needed to describe the clip (both are valid and unchanged).
         //
         // The calling element will only modify its invalidation index since it could belong
         // to part of the inactive stack (that might be restored later). All merged state/geometry
         // is handled by modifying 'added'.
         void updateForElement(RawElement* added, const SaveRecord& current);

         // Updates usage tracking to incorporate the bounds and Z value for the new draw call.
         // If this element hasn't affected any prior draws, it will use the bounds manager to
         // assign itself a compressed painters order for later rendering.
         //
         // Returns whether or not this element clips out the draw with more detailed analysis, and
         // if not, returns the painters order the draw must sort after.
         std::pair<bool, CompressedPaintersOrder> updateForDraw(const BoundsManager* boundsManager,
                                                                const TransformedShape& draw,
                                                                PaintersDepth drawZ);

         // Record a depth-only draw to the given device, restricted to the portion of the clip that
         // is actually required based on prior recorded draws. Resets usage tracking for subsequent
         // passes.
         void drawClip(Device*);

         void validate() const;

     private:
         // TODO: Should only combine elements within the same save record, that don't have pending
         // draws already. Otherwise, we're changing the geometry that will be rasterized and it
         // could lead to gaps even if in a perfect the world the analytically intersected shape was
         // equivalent. Can't combine with other save records, since they *might* become pending
         // later on.
         bool combine(const RawElement& other, const SaveRecord& current);

         // Device space bounds. These bounds are not snapped to pixels with the assumption that if
         // a relation (intersects, contains, etc.) is true for the bounds it will be true for the
         // rasterization of the coordinates that produced those bounds.
         Rect fInnerBounds;
         Rect fOuterBounds;
         // TODO: Convert fOuterBounds to a ComplementRect to make intersection tests faster?
         // Would need to store both original and complement, since the intersection test is
         // Rect + ComplementRect and Element/SaveRecord could be on either side of operation.

         // State tracking how this clip element needs to be recorded into the draw context. As the
         // clip stack is applied to additional draws, the clip's Z and usage bounds grow to account
         // for it; its compressed painter's order is selected the first time a draw is affected.
         Rect fUsageBounds;
         CompressedPaintersOrder fOrder;
         PaintersDepth fMaxZ;

         // Elements are invalidated by SaveRecords as the record is updated with new elements that
         // override old geometry. An invalidated element stores the index of the first element of
         // the save record that invalidated it. This makes it easy to undo when the save record is
         // popped from the stack, and is stable as the current save record is modified.
         int fInvalidatedByIndex;
     };

     // Represents a saved point in the clip stack, and manages the life time of elements added to
     // stack within the record's life time. Also provides the logic for determining active elements
     // given a draw query.
     class SaveRecord {
     public:
         using Stack = SkTBlockList<SaveRecord, 2>;

         explicit SaveRecord(const Rect& deviceBounds);

         SaveRecord(const SaveRecord& prior, int startingElementIndex);

         const SkShader* shader()      const { return fShader.get(); }
         const Rect&     outerBounds() const { return fOuterBounds;  }
         const Rect&     innerBounds() const { return fInnerBounds;  }
         SkClipOp        op()          const { return fStackOp;      }
         ClipState       state()       const;

         int  firstActiveElementIndex() const { return fStartingElementIndex;     }
         int  oldestElementIndex()      const { return fOldestValidIndex;         }
         bool canBeUpdated()            const { return (fDeferredSaveCount == 0); }

         Rect scissor(const Rect& deviceBounds, const Rect& drawBounds) const;

         // Deferred save manipulation
         void pushSave() {
             SkASSERT(fDeferredSaveCount >= 0);
             fDeferredSaveCount++;
         }
         // Returns true if the record should stay alive. False means the ClipStack must delete it
         bool popSave() {
             fDeferredSaveCount--;
             SkASSERT(fDeferredSaveCount >= -1);
             return fDeferredSaveCount >= 0;
         }

         // Return true if the element was added to 'elements', or otherwise affected the save record
         // (e.g. turned it empty).
         bool addElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);

         void addShader(sk_sp<SkShader> shader);

         // Remove the elements owned by this save record, which must happen before the save record
         // itself is removed from the clip stack. Records draws for any removed elements that have
         // draw usages.
         void removeElements(RawElement::Stack* elements, Device*);

         // Restore element validity now that this record is the new top of the stack.
         void restoreElements(RawElement::Stack* elements);

     private:
         // These functions modify 'elements' and element-dependent state of the record
         // (such as valid index and fState). Records draws for any clips that have deferred usages
         // that are inactivated and cannot be restored (i.e. part of the active save record).
         bool appendElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);
         void replaceWithElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);

         // Inner bounds is always contained in outer bounds, or it is empty. All bounds will be
         // contained in the device bounds.
         Rect fInnerBounds; // Inside is full coverage (stack op == intersect) or 0 cov (diff)
         Rect fOuterBounds; // Outside is 0 coverage (op == intersect) or full cov (diff)

         // A save record can have up to one shader, multiple shaders are automatically blended
         sk_sp<SkShader> fShader;

         const int fStartingElementIndex; // First element owned by this save record
         int       fOldestValidIndex;     // Index of oldest element that's valid for this record
         int       fDeferredSaveCount;    // Number of save() calls without modifications (yet)

         // Will be kIntersect unless every valid element is kDifference, which is significant
         // because if kDifference then there is an implicit extra outer bounds at the device edges.
         SkClipOp  fStackOp;
         ClipState fState;
     };

     Rect deviceBounds() const;

     const SaveRecord& currentSaveRecord() const {
         SkASSERT(!fSaves.empty());
         return fSaves.back();
     }

     // Will return the current save record, properly updating deferred saves
     // and initializing a first record if it were empty.
     SaveRecord& writableSaveRecord(bool* wasDeferred);

     RawElement::Stack fElements;
     SaveRecord::Stack fSaves; // always has one wide open record at the top

     Device* fDevice; // the device this clip stack is coupled with
 };

 // Clip element iteration
 class ClipStack::ElementIter {
 public:
     bool operator!=(const ElementIter& o) const {
         return o.fItem != fItem && o.fRemaining != fRemaining;
     }

     const Element& operator*() const { return (*fItem).asElement(); }

     ElementIter& operator++() {
         // Skip over invalidated elements
         do {
             fRemaining--;
             ++fItem;
         } while(fRemaining > 0 && (*fItem).isInvalid());

         return *this;
     }

     ElementIter(RawElement::Stack::CRIter::Item item, int r) : fItem(item), fRemaining(r) {}

     RawElement::Stack::CRIter::Item fItem;
     int fRemaining;

     friend class ClipStack;
 };

 ClipStack::ElementIter ClipStack::begin() const {
     if (this->currentSaveRecord().state() == ClipState::kEmpty ||
         this->currentSaveRecord().state() == ClipState::kWideOpen) {
         // No visible clip elements when empty or wide open
         return this->end();
     }
     int count = fElements.count() - this->currentSaveRecord().oldestElementIndex();
     return ElementIter(fElements.ritems().begin(), count);
 }

 ClipStack::ElementIter ClipStack::end() const {
     return ElementIter(fElements.ritems().end(), 0);
 }

 } // namespace skgpu::graphite

 #endif // skgpu_graphite_ClipStack_DEFINED
	/*
	* Copyright 2022 Google LLC
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#ifndef skgpu_graphite_ClipStack_DEFINED
	#define skgpu_graphite_ClipStack_DEFINED

	#include "include/core/SkClipOp.h"
	#include "src/core/SkTBlockList.h"
	#include "src/gpu/graphite/DrawOrder.h"
	#include "src/gpu/graphite/geom/Shape.h"
	#include "src/gpu/graphite/geom/Transform_graphite.h"

	class SkShader;
	class SkStrokeRec;

	namespace skgpu::graphite {

	class BoundsManager;
	class Clip;
	class Device;
	class Geometry;

	// TODO: Port over many of the unit tests for skgpu/v1/ClipStack defined in GrClipStackTest since
	// those tests do a thorough job of enumerating the different element combinations.
	class ClipStack {
	public:
	// TODO: Some of these states reflect what SkDevice requires. Others are based on what Ganesh
	// could handle analytically. They will likely change as graphite's clips are sorted out
	enum class ClipState : uint8_t {
	kEmpty, kWideOpen, kDeviceRect, kDeviceRRect, kComplex
	};

	// All data describing a geometric modification to the clip
	struct Element {
	Shape fShape;
	Transform fLocalToDevice; // TODO: reference a cached Transform like DrawList?
	SkClipOp fOp;
	};

	// 'owningDevice' must outlive the clip stack.
	ClipStack(Device* owningDevice);

	~ClipStack();

	ClipStack(const ClipStack&) = delete;
	ClipStack& operator=(const ClipStack&) = delete;

	ClipState clipState() const { return this->currentSaveRecord().state(); }
	int maxDeferredClipDraws() const { return fElements.count(); }
	Rect conservativeBounds() const;

	class ElementIter;
	// Provides for-range over active, valid clip elements from most recent to oldest.
	// The iterator provides items as "const Element&".
	inline ElementIter begin() const;
	inline ElementIter end() const;

	// Clip stack manipulation
	void save();
	void restore();

	void clipShape(const Transform& localToDevice, const Shape& shape, SkClipOp op);
	void clipShader(sk_sp<SkShader> shader);

	// Apply the clip stack to the draw described by the provided transform, shape, and stroke.
	// The provided 'z' value is the depth value that the draw will use if it's not clipped out
	// entirely. Applying clips to a draw is a mostly lazy operation except for what is returned:
	// - The Clip's scissor is set to 'conservativeBounds()'.
	// - The Clip stores the draw's clipped bounds, taking into account its transform, styling, and
	// the above scissor.
	// - The CompressedPaintersOrder is the largest order that will be used by any of the clip
	// elements that affect the draw.
	//
	// In addition to computing these values, the clip stack updates per-clip element state for
	// later rendering. Clip shapes that affect draws are later recorded into the Device's
	// DrawContext with their own painter's order chosen to sort earlier than all affected draws
	// but using a Z value greater than affected draws. This ensures that the draws fail the depth
	// test for clipped-out pixels.
	//
	// If the draw is clipped out, the returned draw bounds will be empty.
	std::pair<Clip, CompressedPaintersOrder> applyClipToDraw(const BoundsManager*,
	const Transform&,
	const Geometry&,
	const SkStrokeRec&,
	PaintersDepth z);

	void recordDeferredClipDraws();

	private:
	// SaveRecords and Elements are stored in two parallel stacks. The top-most SaveRecord is the
	// active record, older records represent earlier save points and aren't modified until they
	// become active again. Elements may be owned by the active SaveRecord, in which case they are
	// fully mutable, or they may be owned by a prior SaveRecord. However, Elements from both the
	// active SaveRecord and older records can be valid and affect draw operations. Elements are
	// marked inactive when new elements are determined to supersede their effect completely.
	// Inactive elements of the active SaveRecord can be deleted immediately; inactive elements of
	// older SaveRecords may become active again as the save stack is popped back.
	//
	// See go/grclipstack-2.0 for additional details and visualization of the data structures.
	class SaveRecord;

	// Internally, a lot of clip reasoning is based on an op, outer bounds, and whether a shape
	// contains another (possibly just conservatively based on inner/outer device-space bounds).
	// Element and SaveRecord store this information directly. A draw is equivalent to a clip
	// element with the intersection op. TransformedShape is a lightweight wrapper that can convert
	// these different types into a common type that Simplify() can reason about.
	struct TransformedShape;
	// This captures which of the two elements in (A op B) would be required when they are combined,
	// where op is intersect or difference.
	enum class SimplifyResult {
	kEmpty,
	kAOnly,
	kBOnly,
	kBoth
	};
	static SimplifyResult Simplify(const TransformedShape& a, const TransformedShape& b);

	// Wraps the geometric Element data with logic for containment and bounds testing.
	class RawElement : private Element {
	public:
	using Stack = SkTBlockList<RawElement, 1>;

	RawElement(const Rect& deviceBounds,
	const Transform& localToDevice,
	const Shape& shape,
	SkClipOp op);

	~RawElement() {
	// A pending draw means the element affects something already recorded, so its own
	// shape needs to be recorded as a draw. Since recording requires the Device (and
	// DrawContext), it must happen before we destroy the element itself.
	SkASSERT(!this->hasPendingDraw());
	}

	// Silence warnings about implicit copy ctor/assignment because we're declaring a dtor
	RawElement(const RawElement&) = default;
	RawElement& operator=(const RawElement&) = default;

	operator TransformedShape() const;

	const Element& asElement() const { return *this; }
	bool hasPendingDraw() const { return fOrder != DrawOrder::kNoIntersection; }

	const Shape& shape() const { return fShape; }
	const Transform& localToDevice() const { return fLocalToDevice; }
	const Rect& outerBounds() const { return fOuterBounds; }
	const Rect& innerBounds() const { return fInnerBounds; }
	SkClipOp op() const { return fOp; }
	ClipState clipType() const;

	// As new elements are pushed on to the stack, they may make older elements redundant.
	// The old elements are marked invalid so they are skipped during clip application, but may
	// become active again when a save record is restored.
	bool isInvalid() const { return fInvalidatedByIndex >= 0; }
	void markInvalid(const SaveRecord& current);
	void restoreValid(const SaveRecord& current);

	// 'added' represents a new op added to the element stack. Its combination with this element
	// can result in a number of possibilities:
	// 1. The entire clip is empty (signaled by both this and 'added' being invalidated).
	// 2. The 'added' op supercedes this element (this element is invalidated).
	// 3. This op supercedes the 'added' element (the added element is marked invalidated).
	// 4. Their combination can be represented by a single new op (in which case this
	// element should be invalidated, and the combined shape stored in 'added').
	// 5. Or both elements remain needed to describe the clip (both are valid and unchanged).
	//
	// The calling element will only modify its invalidation index since it could belong
	// to part of the inactive stack (that might be restored later). All merged state/geometry
	// is handled by modifying 'added'.
	void updateForElement(RawElement* added, const SaveRecord& current);

	// Updates usage tracking to incorporate the bounds and Z value for the new draw call.
	// If this element hasn't affected any prior draws, it will use the bounds manager to
	// assign itself a compressed painters order for later rendering.
	//
	// Returns whether or not this element clips out the draw with more detailed analysis, and
	// if not, returns the painters order the draw must sort after.
	std::pair<bool, CompressedPaintersOrder> updateForDraw(const BoundsManager* boundsManager,
	const TransformedShape& draw,
	PaintersDepth drawZ);

	// Record a depth-only draw to the given device, restricted to the portion of the clip that
	// is actually required based on prior recorded draws. Resets usage tracking for subsequent
	// passes.
	void drawClip(Device*);

	void validate() const;

	private:
	// TODO: Should only combine elements within the same save record, that don't have pending
	// draws already. Otherwise, we're changing the geometry that will be rasterized and it
	// could lead to gaps even if in a perfect the world the analytically intersected shape was
	// equivalent. Can't combine with other save records, since they might become pending
	// later on.
	bool combine(const RawElement& other, const SaveRecord& current);

	// Device space bounds. These bounds are not snapped to pixels with the assumption that if
	// a relation (intersects, contains, etc.) is true for the bounds it will be true for the
	// rasterization of the coordinates that produced those bounds.
	Rect fInnerBounds;
	Rect fOuterBounds;
	// TODO: Convert fOuterBounds to a ComplementRect to make intersection tests faster?
	// Would need to store both original and complement, since the intersection test is
	// Rect + ComplementRect and Element/SaveRecord could be on either side of operation.

	// State tracking how this clip element needs to be recorded into the draw context. As the
	// clip stack is applied to additional draws, the clip's Z and usage bounds grow to account
	// for it; its compressed painter's order is selected the first time a draw is affected.
	Rect fUsageBounds;
	CompressedPaintersOrder fOrder;
	PaintersDepth fMaxZ;

	// Elements are invalidated by SaveRecords as the record is updated with new elements that
	// override old geometry. An invalidated element stores the index of the first element of
	// the save record that invalidated it. This makes it easy to undo when the save record is
	// popped from the stack, and is stable as the current save record is modified.
	int fInvalidatedByIndex;
	};

	// Represents a saved point in the clip stack, and manages the life time of elements added to
	// stack within the record's life time. Also provides the logic for determining active elements
	// given a draw query.
	class SaveRecord {
	public:
	using Stack = SkTBlockList<SaveRecord, 2>;

	explicit SaveRecord(const Rect& deviceBounds);

	SaveRecord(const SaveRecord& prior, int startingElementIndex);

	const SkShader* shader() const { return fShader.get(); }
	const Rect& outerBounds() const { return fOuterBounds; }
	const Rect& innerBounds() const { return fInnerBounds; }
	SkClipOp op() const { return fStackOp; }
	ClipState state() const;

	int firstActiveElementIndex() const { return fStartingElementIndex; }
	int oldestElementIndex() const { return fOldestValidIndex; }
	bool canBeUpdated() const { return (fDeferredSaveCount == 0); }

	Rect scissor(const Rect& deviceBounds, const Rect& drawBounds) const;

	// Deferred save manipulation
	void pushSave() {
	SkASSERT(fDeferredSaveCount >= 0);
	fDeferredSaveCount++;
	}
	// Returns true if the record should stay alive. False means the ClipStack must delete it
	bool popSave() {
	fDeferredSaveCount--;
	SkASSERT(fDeferredSaveCount >= -1);
	return fDeferredSaveCount >= 0;
	}

	// Return true if the element was added to 'elements', or otherwise affected the save record
	// (e.g. turned it empty).
	bool addElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);

	void addShader(sk_sp<SkShader> shader);

	// Remove the elements owned by this save record, which must happen before the save record
	// itself is removed from the clip stack. Records draws for any removed elements that have
	// draw usages.
	void removeElements(RawElement::Stack* elements, Device*);

	// Restore element validity now that this record is the new top of the stack.
	void restoreElements(RawElement::Stack* elements);

	private:
	// These functions modify 'elements' and element-dependent state of the record
	// (such as valid index and fState). Records draws for any clips that have deferred usages
	// that are inactivated and cannot be restored (i.e. part of the active save record).
	bool appendElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);
	void replaceWithElement(RawElement&& toAdd, RawElement::Stack* elements, Device*);

	// Inner bounds is always contained in outer bounds, or it is empty. All bounds will be
	// contained in the device bounds.
	Rect fInnerBounds; // Inside is full coverage (stack op == intersect) or 0 cov (diff)
	Rect fOuterBounds; // Outside is 0 coverage (op == intersect) or full cov (diff)

	// A save record can have up to one shader, multiple shaders are automatically blended
	sk_sp<SkShader> fShader;

	const int fStartingElementIndex; // First element owned by this save record
	int fOldestValidIndex; // Index of oldest element that's valid for this record
	int fDeferredSaveCount; // Number of save() calls without modifications (yet)

	// Will be kIntersect unless every valid element is kDifference, which is significant
	// because if kDifference then there is an implicit extra outer bounds at the device edges.
	SkClipOp fStackOp;
	ClipState fState;
	};

	Rect deviceBounds() const;

	const SaveRecord& currentSaveRecord() const {
	SkASSERT(!fSaves.empty());
	return fSaves.back();
	}

	// Will return the current save record, properly updating deferred saves
	// and initializing a first record if it were empty.
	SaveRecord& writableSaveRecord(bool* wasDeferred);

	RawElement::Stack fElements;
	SaveRecord::Stack fSaves; // always has one wide open record at the top

	Device* fDevice; // the device this clip stack is coupled with
	};

	// Clip element iteration
	class ClipStack::ElementIter {
	public:
	bool operator!=(const ElementIter& o) const {
	return o.fItem != fItem && o.fRemaining != fRemaining;
	}

	const Element& operator() const { return (fItem).asElement(); }

	ElementIter& operator++() {
	// Skip over invalidated elements
	do {
	fRemaining--;
	++fItem;
	} while(fRemaining > 0 && (*fItem).isInvalid());

	return *this;
	}

	ElementIter(RawElement::Stack::CRIter::Item item, int r) : fItem(item), fRemaining(r) {}

	RawElement::Stack::CRIter::Item fItem;
	int fRemaining;

	friend class ClipStack;
	};

	ClipStack::ElementIter ClipStack::begin() const {
	if (this->currentSaveRecord().state() == ClipState::kEmpty \|\|
	this->currentSaveRecord().state() == ClipState::kWideOpen) {
	// No visible clip elements when empty or wide open
	return this->end();
	}
	int count = fElements.count() - this->currentSaveRecord().oldestElementIndex();
	return ElementIter(fElements.ritems().begin(), count);
	}

	ClipStack::ElementIter ClipStack::end() const {
	return ElementIter(fElements.ritems().end(), 0);
	}

	} // namespace skgpu::graphite

	#endif // skgpu_graphite_ClipStack_DEFINED