src/gpu/geometry/GrQuadBuffer.h - skia - Git at Google

 /*
  * Copyright 2019 Google LLC
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef GrQuadBuffer_DEFINED
 #define GrQuadBuffer_DEFINED

 #include "include/private/SkTDArray.h"
 #include "src/gpu/geometry/GrQuad.h"

 template<typename T>
 class GrQuadBuffer {
 public:
     GrQuadBuffer()
             : fCount(0)
             , fDeviceType(GrQuad::Type::kAxisAligned)
             , fLocalType(GrQuad::Type::kAxisAligned) {
         // Pre-allocate space for 1 2D device-space quad, metadata, and header
         fData.reserve(this->entrySize(fDeviceType, nullptr));
     }

     // Reserves space for the given number of entries; if 'needsLocals' is true, space will be
     // reserved for each entry to also have a 2D local quad. The reserved space assumes 2D device
     // quad for simplicity. Since this buffer has a variable bitrate encoding for quads, this may
     // over or under reserve, but pre-allocating still helps when possible.
     GrQuadBuffer(int count, bool needsLocals = false)
             : fCount(0)
             , fDeviceType(GrQuad::Type::kAxisAligned)
             , fLocalType(GrQuad::Type::kAxisAligned) {
         int entrySize = this->entrySize(fDeviceType, needsLocals ? &fLocalType : nullptr);
         fData.reserve(count * entrySize);
     }

     // The number of device-space quads (and metadata, and optional local quads) that are in the
     // the buffer.
     int count() const { return fCount; }

     // The most general type for the device-space quads in this buffer
     GrQuad::Type deviceQuadType() const { return fDeviceType; }

     // The most general type for the local quads; if no local quads are ever added, this will
     // return kAxisAligned.
     GrQuad::Type localQuadType() const { return fLocalType; }

     // Append the given 'deviceQuad' to this buffer, with its associated 'metadata'. If 'localQuad'
     // is not null, the local coordinates will also be attached to the entry. When an entry
     // has local coordinates, during iteration, the Iter::hasLocals() will return true and its
     // Iter::localQuad() will be equivalent to the provided local coordinates. If 'localQuad' is
     // null then Iter::hasLocals() will report false for the added entry.
     void append(const GrQuad& deviceQuad, T&& metadata, const GrQuad* localQuad = nullptr);

     // Copies all entries from 'that' to this buffer
     void concat(const GrQuadBuffer<T>& that);

     // Provides a read-only iterator over a quad buffer, giving access to the device quad, metadata
     // and optional local quad.
     class Iter {
     public:
         Iter(const GrQuadBuffer<T>* buffer)
                 : fDeviceQuad(SkRect::MakeEmpty())
                 , fLocalQuad(SkRect::MakeEmpty())
                 , fBuffer(buffer)
                 , fCurrentEntry(nullptr)
                 , fNextEntry(buffer->fData.begin()) {
             SkDEBUGCODE(fExpectedCount = buffer->count();)
         }

         bool next();

         const T& metadata() const { this->validate(); return *(fBuffer->metadata(fCurrentEntry)); }

         // The returned pointer is mutable so that the object can be used for scratch calculations
         // during op preparation. However, any changes are not persisted in the GrQuadBuffer and
         // subsequent calls to next() will overwrite the state of the GrQuad.
         GrQuad* deviceQuad() { this->validate(); return &fDeviceQuad; }

         // If isLocalValid() returns false, this returns nullptr. Otherwise, the returned pointer
         // is mutable in the same manner as deviceQuad().
         GrQuad* localQuad() {
             this->validate();
             return this->isLocalValid() ? &fLocalQuad : nullptr;
         }

         bool isLocalValid() const {
             this->validate();
             return fBuffer->header(fCurrentEntry)->fHasLocals;
         }

     private:
         // Quads are stored locally so that calling code doesn't need to re-declare their own quads
         GrQuad fDeviceQuad;
         GrQuad fLocalQuad;

         const GrQuadBuffer<T>* fBuffer;
         // The pointer to the current entry to read metadata/header details from
         const char* fCurrentEntry;
         // The pointer to replace fCurrentEntry when next() is called, cached since it is calculated
         // automatically while unpacking the quad data.
         const char* fNextEntry;

         SkDEBUGCODE(int fExpectedCount;)

         void validate() const {
             SkDEBUGCODE(fBuffer->validate(fCurrentEntry, fExpectedCount);)
         }
     };

     Iter iterator() const { return Iter(this); }

     // Provides a *mutable* iterator over just the metadata stored in the quad buffer. This skips
     // unpacking the device and local quads into GrQuads and is intended for use during op
     // finalization, which may require rewriting state such as color.
     class MetadataIter {
     public:
         MetadataIter(GrQuadBuffer<T>* list)
                 : fBuffer(list)
                 , fCurrentEntry(nullptr) {
             SkDEBUGCODE(fExpectedCount = list->count();)
         }

         bool next();

         T& operator*() { this->validate(); return *(fBuffer->metadata(fCurrentEntry)); }

         T* operator->() { this->validate(); return fBuffer->metadata(fCurrentEntry); }

     private:
         GrQuadBuffer<T>* fBuffer;
         char* fCurrentEntry;

         SkDEBUGCODE(int fExpectedCount;)

         void validate() const {
             SkDEBUGCODE(fBuffer->validate(fCurrentEntry, fExpectedCount);)
         }
     };

     MetadataIter metadata() { return MetadataIter(this); }

 private:
     struct alignas(int32_t) Header {
         unsigned fDeviceType : 2;
         unsigned fLocalType  : 2; // Ignore if fHasLocals is false
         unsigned fHasLocals  : 1;
         // Known value to detect if iteration doesn't properly advance through the buffer
         SkDEBUGCODE(unsigned fSentinel : 27;)
     };
     static_assert(sizeof(Header) == sizeof(int32_t), "Header should be 4 bytes");

     static constexpr unsigned kSentinel = 0xbaffe;
     static constexpr int kMetaSize = sizeof(Header) + sizeof(T);
     static constexpr int k2DQuadFloats = 8;
     static constexpr int k3DQuadFloats = 12;

     // Each logical entry in the buffer is a variable length tuple storing device coordinates,
     // optional local coordinates, and metadata. An entry always has a header that defines the
     // quad types of device and local coordinates, and always has metadata of type T. The device
     // and local quads' data follows as a variable length array of floats:
     //  [ header    ] = 4 bytes
     //  [ metadata  ] = sizeof(T), assert alignof(T) == 4 so that pointer casts are valid
     //  [ device xs ] = 4 floats = 16 bytes
     //  [ device ys ] = 4 floats
     //  [ device ws ] = 4 floats or 0 floats depending on fDeviceType in header
     //  [ local xs  ] = 4 floats or 0 floats depending on fHasLocals in header
     //  [ local ys  ] = 4 floats or 0 floats depending on fHasLocals in header
     //  [ local ws  ] = 4 floats or 0 floats depending on fHasLocals and fLocalType in header
     // FIXME (michaelludwig) - Since this is intended only for ops, can we use the arena to
     //      allocate storage for the quad buffer? Since this is forward-iteration only, could also
     //      explore a linked-list structure for concatenating quads when batching ops
     SkTDArray<char> fData;

     int fCount; // Number of (device, local, metadata) entries
     GrQuad::Type fDeviceType; // Most general type of all entries
     GrQuad::Type fLocalType;

     inline int entrySize(GrQuad::Type deviceType, const GrQuad::Type* localType) const {
         int size = kMetaSize;
         size += (deviceType == GrQuad::Type::kPerspective ? k3DQuadFloats
                                                           : k2DQuadFloats) * sizeof(float);
         if (localType) {
             size += (*localType == GrQuad::Type::kPerspective ? k3DQuadFloats
                                                               : k2DQuadFloats) * sizeof(float);
         }
         return size;
     }
     inline int entrySize(const Header* header) const {
         if (header->fHasLocals) {
             GrQuad::Type localType = static_cast<GrQuad::Type>(header->fLocalType);
             return this->entrySize(static_cast<GrQuad::Type>(header->fDeviceType), &localType);
         } else {
             return this->entrySize(static_cast<GrQuad::Type>(header->fDeviceType), nullptr);
         }
     }

     // Helpers to access typed sections of the buffer, given the start of an entry
     inline Header* header(char* entry) {
         return static_cast<Header*>(static_cast<void*>(entry));
     }
     inline const Header* header(const char* entry) const {
         return static_cast<const Header*>(static_cast<const void*>(entry));
     }

     inline T* metadata(char* entry) {
         return static_cast<T*>(static_cast<void*>(entry + sizeof(Header)));
     }
     inline const T* metadata(const char* entry) const {
         return static_cast<const T*>(static_cast<const void*>(entry + sizeof(Header)));
     }

     inline float* coords(char* entry) {
         return static_cast<float*>(static_cast<void*>(entry + kMetaSize));
     }
     inline const float* coords(const char* entry) const {
         return static_cast<const float*>(static_cast<const void*>(entry + kMetaSize));
     }

     // Helpers to convert from coordinates to GrQuad and vice versa, returning pointer to the
     // next packed quad coordinates.
     float* packQuad(const GrQuad& quad, float* coords);
     const float* unpackQuad(GrQuad::Type type, const float* coords, GrQuad* quad) const;

 #ifdef SK_DEBUG
     void validate(const char* entry, int expectedCount) const;
 #endif
 };

 ///////////////////////////////////////////////////////////////////////////////////////////////////
 // Buffer implementation
 ///////////////////////////////////////////////////////////////////////////////////////////////////

 template<typename T>
 float* GrQuadBuffer<T>::packQuad(const GrQuad& quad, float* coords) {
     // Copies all 12 (or 8) floats at once, so requires the 3 arrays to be contiguous
     // FIXME(michaelludwig) - If this turns out not to be the case, just do 4 copies
     SkASSERT(quad.xs() + 4 == quad.ys() && quad.xs() + 8 == quad.ws());
     if (quad.hasPerspective()) {
         memcpy(coords, quad.xs(), k3DQuadFloats * sizeof(float));
         return coords + k3DQuadFloats;
     } else {
         memcpy(coords, quad.xs(), k2DQuadFloats * sizeof(float));
         return coords + k2DQuadFloats;
     }
 }

 template<typename T>
 const float* GrQuadBuffer<T>::unpackQuad(GrQuad::Type type, const float* coords, GrQuad* quad) const {
     SkASSERT(quad->xs() + 4 == quad->ys() && quad->xs() + 8 == quad->ws());
     if (type == GrQuad::Type::kPerspective) {
         // Fill in X, Y, and W in one go
         memcpy(quad->xs(), coords, k3DQuadFloats * sizeof(float));
         coords = coords + k3DQuadFloats;
     } else {
         // Fill in X and Y of the quad, the setQuadType() below will set Ws to 1 if needed
         memcpy(quad->xs(), coords, k2DQuadFloats * sizeof(float));
         coords = coords + k2DQuadFloats;
     }

     quad->setQuadType(type);
     return coords;
 }

 template<typename T>
 void GrQuadBuffer<T>::append(const GrQuad& deviceQuad, T&& metadata, const GrQuad* localQuad) {
     GrQuad::Type localType = localQuad ? localQuad->quadType() : GrQuad::Type::kAxisAligned;
     int entrySize = this->entrySize(deviceQuad.quadType(), localQuad ? &localType : nullptr);

     // Fill in the entry, as described in fData's declaration
     char* entry = fData.append(entrySize);
     // First the header
     Header* h = this->header(entry);
     h->fDeviceType = static_cast<unsigned>(deviceQuad.quadType());
     h->fHasLocals = static_cast<unsigned>(localQuad != nullptr);
     h->fLocalType = static_cast<unsigned>(localQuad ? localQuad->quadType()
                                                     : GrQuad::Type::kAxisAligned);
     SkDEBUGCODE(h->fSentinel = static_cast<unsigned>(kSentinel);)

     // Second, the fixed-size metadata
     static_assert(alignof(T) == 4, "Metadata must be 4 byte aligned");
     *(this->metadata(entry)) = std::move(metadata);

     // Then the variable blocks of x, y, and w float coordinates
     float* coords = this->coords(entry);
     coords = this->packQuad(deviceQuad, coords);
     if (localQuad) {
         coords = this->packQuad(*localQuad, coords);
     }
     SkASSERT((char*)coords - entry == entrySize);

     // Entry complete, update buffer-level state
     fCount++;
     if (deviceQuad.quadType() > fDeviceType) {
         fDeviceType = deviceQuad.quadType();
     }
     if (localQuad && localQuad->quadType() > fLocalType) {
         fLocalType = localQuad->quadType();
     }
 }

 template<typename T>
 void GrQuadBuffer<T>::concat(const GrQuadBuffer<T>& that) {
     fData.append(that.fData.count(), that.fData.begin());
     fCount += that.fCount;
     if (that.fDeviceType > fDeviceType) {
         fDeviceType = that.fDeviceType;
     }
     if (that.fLocalType > fLocalType) {
         fLocalType = that.fLocalType;
     }
 }

 #ifdef SK_DEBUG
 template<typename T>
 void GrQuadBuffer<T>::validate(const char* entry, int expectedCount) const {
     // Triggers if accessing before next() is called on an iterator
     SkASSERT(entry);
     // Triggers if accessing after next() returns false
     SkASSERT(entry < fData.end());
     // Triggers if elements have been added to the buffer while iterating entries
     SkASSERT(expectedCount == fCount);
     // Make sure the start of the entry looks like a header
     SkASSERT(this->header(entry)->fSentinel == kSentinel);
 }
 #endif

 ///////////////////////////////////////////////////////////////////////////////////////////////////
 // Iterator implementations
 ///////////////////////////////////////////////////////////////////////////////////////////////////

 template<typename T>
 bool GrQuadBuffer<T>::Iter::next() {
     SkASSERT(fNextEntry);
     if (fNextEntry >= fBuffer->fData.end()) {
         return false;
     }
     // There is at least one more entry, so store the current start for metadata access
     fCurrentEntry = fNextEntry;

     // And then unpack the device and optional local coordinates into fDeviceQuad and fLocalQuad
     const Header* h = fBuffer->header(fCurrentEntry);
     const float* coords = fBuffer->coords(fCurrentEntry);
     coords = fBuffer->unpackQuad(static_cast<GrQuad::Type>(h->fDeviceType), coords, &fDeviceQuad);
     if (h->fHasLocals) {
         coords = fBuffer->unpackQuad(static_cast<GrQuad::Type>(h->fLocalType), coords, &fLocalQuad);
     } // else localQuad() will return a nullptr so no need to reset fLocalQuad

     // At this point, coords points to the start of the next entry
     fNextEntry = static_cast<const char*>(static_cast<const void*>(coords));
     SkASSERT((fNextEntry - fCurrentEntry) == fBuffer->entrySize(h));
     return true;
 }

 template<typename T>
 bool GrQuadBuffer<T>::MetadataIter::next() {
     if (fCurrentEntry) {
         // Advance pointer by entry size
         if (fCurrentEntry < fBuffer->fData.end()) {
             const Header* h = fBuffer->header(fCurrentEntry);
             fCurrentEntry += fBuffer->entrySize(h);
         }
     } else {
         // First call to next
         fCurrentEntry = fBuffer->fData.begin();
     }
     // Nothing else is needed to do but report whether or not the updated pointer is valid
     return fCurrentEntry < fBuffer->fData.end();
 }
 #endif  // GrQuadBuffer_DEFINED
	/*
	* Copyright 2019 Google LLC
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/
	#ifndef GrQuadBuffer_DEFINED
	#define GrQuadBuffer_DEFINED

	#include "include/private/SkTDArray.h"
	#include "src/gpu/geometry/GrQuad.h"

	template<typename T>
	class GrQuadBuffer {
	public:
	GrQuadBuffer()
	: fCount(0)
	, fDeviceType(GrQuad::Type::kAxisAligned)
	, fLocalType(GrQuad::Type::kAxisAligned) {
	// Pre-allocate space for 1 2D device-space quad, metadata, and header
	fData.reserve(this->entrySize(fDeviceType, nullptr));
	}

	// Reserves space for the given number of entries; if 'needsLocals' is true, space will be
	// reserved for each entry to also have a 2D local quad. The reserved space assumes 2D device
	// quad for simplicity. Since this buffer has a variable bitrate encoding for quads, this may
	// over or under reserve, but pre-allocating still helps when possible.
	GrQuadBuffer(int count, bool needsLocals = false)
	: fCount(0)
	, fDeviceType(GrQuad::Type::kAxisAligned)
	, fLocalType(GrQuad::Type::kAxisAligned) {
	int entrySize = this->entrySize(fDeviceType, needsLocals ? &fLocalType : nullptr);
	fData.reserve(count * entrySize);
	}

	// The number of device-space quads (and metadata, and optional local quads) that are in the
	// the buffer.
	int count() const { return fCount; }

	// The most general type for the device-space quads in this buffer
	GrQuad::Type deviceQuadType() const { return fDeviceType; }

	// The most general type for the local quads; if no local quads are ever added, this will
	// return kAxisAligned.
	GrQuad::Type localQuadType() const { return fLocalType; }

	// Append the given 'deviceQuad' to this buffer, with its associated 'metadata'. If 'localQuad'
	// is not null, the local coordinates will also be attached to the entry. When an entry
	// has local coordinates, during iteration, the Iter::hasLocals() will return true and its
	// Iter::localQuad() will be equivalent to the provided local coordinates. If 'localQuad' is
	// null then Iter::hasLocals() will report false for the added entry.
	void append(const GrQuad& deviceQuad, T&& metadata, const GrQuad* localQuad = nullptr);

	// Copies all entries from 'that' to this buffer
	void concat(const GrQuadBuffer<T>& that);

	// Provides a read-only iterator over a quad buffer, giving access to the device quad, metadata
	// and optional local quad.
	class Iter {
	public:
	Iter(const GrQuadBuffer<T>* buffer)
	: fDeviceQuad(SkRect::MakeEmpty())
	, fLocalQuad(SkRect::MakeEmpty())
	, fBuffer(buffer)
	, fCurrentEntry(nullptr)
	, fNextEntry(buffer->fData.begin()) {
	SkDEBUGCODE(fExpectedCount = buffer->count();)
	}

	bool next();

	const T& metadata() const { this->validate(); return *(fBuffer->metadata(fCurrentEntry)); }

	// The returned pointer is mutable so that the object can be used for scratch calculations
	// during op preparation. However, any changes are not persisted in the GrQuadBuffer and
	// subsequent calls to next() will overwrite the state of the GrQuad.
	GrQuad* deviceQuad() { this->validate(); return &fDeviceQuad; }

	// If isLocalValid() returns false, this returns nullptr. Otherwise, the returned pointer
	// is mutable in the same manner as deviceQuad().
	GrQuad* localQuad() {
	this->validate();
	return this->isLocalValid() ? &fLocalQuad : nullptr;
	}

	bool isLocalValid() const {
	this->validate();
	return fBuffer->header(fCurrentEntry)->fHasLocals;
	}

	private:
	// Quads are stored locally so that calling code doesn't need to re-declare their own quads
	GrQuad fDeviceQuad;
	GrQuad fLocalQuad;

	const GrQuadBuffer<T>* fBuffer;
	// The pointer to the current entry to read metadata/header details from
	const char* fCurrentEntry;
	// The pointer to replace fCurrentEntry when next() is called, cached since it is calculated
	// automatically while unpacking the quad data.
	const char* fNextEntry;

	SkDEBUGCODE(int fExpectedCount;)

	void validate() const {
	SkDEBUGCODE(fBuffer->validate(fCurrentEntry, fExpectedCount);)
	}
	};

	Iter iterator() const { return Iter(this); }

	// Provides a mutable iterator over just the metadata stored in the quad buffer. This skips
	// unpacking the device and local quads into GrQuads and is intended for use during op
	// finalization, which may require rewriting state such as color.
	class MetadataIter {
	public:
	MetadataIter(GrQuadBuffer<T>* list)
	: fBuffer(list)
	, fCurrentEntry(nullptr) {
	SkDEBUGCODE(fExpectedCount = list->count();)
	}

	bool next();

	T& operator() { this->validate(); return (fBuffer->metadata(fCurrentEntry)); }

	T* operator->() { this->validate(); return fBuffer->metadata(fCurrentEntry); }

	private:
	GrQuadBuffer<T>* fBuffer;
	char* fCurrentEntry;

	SkDEBUGCODE(int fExpectedCount;)

	void validate() const {
	SkDEBUGCODE(fBuffer->validate(fCurrentEntry, fExpectedCount);)
	}
	};

	MetadataIter metadata() { return MetadataIter(this); }

	private:
	struct alignas(int32_t) Header {
	unsigned fDeviceType : 2;
	unsigned fLocalType : 2; // Ignore if fHasLocals is false
	unsigned fHasLocals : 1;
	// Known value to detect if iteration doesn't properly advance through the buffer
	SkDEBUGCODE(unsigned fSentinel : 27;)
	};
	static_assert(sizeof(Header) == sizeof(int32_t), "Header should be 4 bytes");

	static constexpr unsigned kSentinel = 0xbaffe;
	static constexpr int kMetaSize = sizeof(Header) + sizeof(T);
	static constexpr int k2DQuadFloats = 8;
	static constexpr int k3DQuadFloats = 12;

	// Each logical entry in the buffer is a variable length tuple storing device coordinates,
	// optional local coordinates, and metadata. An entry always has a header that defines the
	// quad types of device and local coordinates, and always has metadata of type T. The device
	// and local quads' data follows as a variable length array of floats:
	// [ header ] = 4 bytes
	// [ metadata ] = sizeof(T), assert alignof(T) == 4 so that pointer casts are valid
	// [ device xs ] = 4 floats = 16 bytes
	// [ device ys ] = 4 floats
	// [ device ws ] = 4 floats or 0 floats depending on fDeviceType in header
	// [ local xs ] = 4 floats or 0 floats depending on fHasLocals in header
	// [ local ys ] = 4 floats or 0 floats depending on fHasLocals in header
	// [ local ws ] = 4 floats or 0 floats depending on fHasLocals and fLocalType in header
	// FIXME (michaelludwig) - Since this is intended only for ops, can we use the arena to
	// allocate storage for the quad buffer? Since this is forward-iteration only, could also
	// explore a linked-list structure for concatenating quads when batching ops
	SkTDArray<char> fData;

	int fCount; // Number of (device, local, metadata) entries
	GrQuad::Type fDeviceType; // Most general type of all entries
	GrQuad::Type fLocalType;

	inline int entrySize(GrQuad::Type deviceType, const GrQuad::Type* localType) const {
	int size = kMetaSize;
	size += (deviceType == GrQuad::Type::kPerspective ? k3DQuadFloats
	: k2DQuadFloats) * sizeof(float);
	if (localType) {
	size += (*localType == GrQuad::Type::kPerspective ? k3DQuadFloats
	: k2DQuadFloats) * sizeof(float);
	}
	return size;
	}
	inline int entrySize(const Header* header) const {
	if (header->fHasLocals) {
	GrQuad::Type localType = static_cast<GrQuad::Type>(header->fLocalType);
	return this->entrySize(static_cast<GrQuad::Type>(header->fDeviceType), &localType);
	} else {
	return this->entrySize(static_cast<GrQuad::Type>(header->fDeviceType), nullptr);
	}
	}

	// Helpers to access typed sections of the buffer, given the start of an entry
	inline Header* header(char* entry) {
	return static_cast<Header>(static_cast<void>(entry));
	}
	inline const Header* header(const char* entry) const {
	return static_cast<const Header>(static_cast<const void>(entry));
	}

	inline T* metadata(char* entry) {
	return static_cast<T>(static_cast<void>(entry + sizeof(Header)));
	}
	inline const T* metadata(const char* entry) const {
	return static_cast<const T>(static_cast<const void>(entry + sizeof(Header)));
	}

	inline float* coords(char* entry) {
	return static_cast<float>(static_cast<void>(entry + kMetaSize));
	}
	inline const float* coords(const char* entry) const {
	return static_cast<const float>(static_cast<const void>(entry + kMetaSize));
	}

	// Helpers to convert from coordinates to GrQuad and vice versa, returning pointer to the
	// next packed quad coordinates.
	float* packQuad(const GrQuad& quad, float* coords);
	const float* unpackQuad(GrQuad::Type type, const float* coords, GrQuad* quad) const;

	#ifdef SK_DEBUG
	void validate(const char* entry, int expectedCount) const;
	#endif
	};

	///////////////////////////////////////////////////////////////////////////////////////////////////
	// Buffer implementation
	///////////////////////////////////////////////////////////////////////////////////////////////////

	template<typename T>
	float* GrQuadBuffer<T>::packQuad(const GrQuad& quad, float* coords) {
	// Copies all 12 (or 8) floats at once, so requires the 3 arrays to be contiguous
	// FIXME(michaelludwig) - If this turns out not to be the case, just do 4 copies
	SkASSERT(quad.xs() + 4 == quad.ys() && quad.xs() + 8 == quad.ws());
	if (quad.hasPerspective()) {
	memcpy(coords, quad.xs(), k3DQuadFloats * sizeof(float));
	return coords + k3DQuadFloats;
	} else {
	memcpy(coords, quad.xs(), k2DQuadFloats * sizeof(float));
	return coords + k2DQuadFloats;
	}
	}

	template<typename T>
	const float* GrQuadBuffer<T>::unpackQuad(GrQuad::Type type, const float* coords, GrQuad* quad) const {
	SkASSERT(quad->xs() + 4 == quad->ys() && quad->xs() + 8 == quad->ws());
	if (type == GrQuad::Type::kPerspective) {
	// Fill in X, Y, and W in one go
	memcpy(quad->xs(), coords, k3DQuadFloats * sizeof(float));
	coords = coords + k3DQuadFloats;
	} else {
	// Fill in X and Y of the quad, the setQuadType() below will set Ws to 1 if needed
	memcpy(quad->xs(), coords, k2DQuadFloats * sizeof(float));
	coords = coords + k2DQuadFloats;
	}

	quad->setQuadType(type);
	return coords;
	}

	template<typename T>
	void GrQuadBuffer<T>::append(const GrQuad& deviceQuad, T&& metadata, const GrQuad* localQuad) {
	GrQuad::Type localType = localQuad ? localQuad->quadType() : GrQuad::Type::kAxisAligned;
	int entrySize = this->entrySize(deviceQuad.quadType(), localQuad ? &localType : nullptr);

	// Fill in the entry, as described in fData's declaration
	char* entry = fData.append(entrySize);
	// First the header
	Header* h = this->header(entry);
	h->fDeviceType = static_cast<unsigned>(deviceQuad.quadType());
	h->fHasLocals = static_cast<unsigned>(localQuad != nullptr);
	h->fLocalType = static_cast<unsigned>(localQuad ? localQuad->quadType()
	: GrQuad::Type::kAxisAligned);
	SkDEBUGCODE(h->fSentinel = static_cast<unsigned>(kSentinel);)

	// Second, the fixed-size metadata
	static_assert(alignof(T) == 4, "Metadata must be 4 byte aligned");
	*(this->metadata(entry)) = std::move(metadata);

	// Then the variable blocks of x, y, and w float coordinates
	float* coords = this->coords(entry);
	coords = this->packQuad(deviceQuad, coords);
	if (localQuad) {
	coords = this->packQuad(*localQuad, coords);
	}
	SkASSERT((char*)coords - entry == entrySize);

	// Entry complete, update buffer-level state
	fCount++;
	if (deviceQuad.quadType() > fDeviceType) {
	fDeviceType = deviceQuad.quadType();
	}
	if (localQuad && localQuad->quadType() > fLocalType) {
	fLocalType = localQuad->quadType();
	}
	}

	template<typename T>
	void GrQuadBuffer<T>::concat(const GrQuadBuffer<T>& that) {
	fData.append(that.fData.count(), that.fData.begin());
	fCount += that.fCount;
	if (that.fDeviceType > fDeviceType) {
	fDeviceType = that.fDeviceType;
	}
	if (that.fLocalType > fLocalType) {
	fLocalType = that.fLocalType;
	}
	}

	#ifdef SK_DEBUG
	template<typename T>
	void GrQuadBuffer<T>::validate(const char* entry, int expectedCount) const {
	// Triggers if accessing before next() is called on an iterator
	SkASSERT(entry);
	// Triggers if accessing after next() returns false
	SkASSERT(entry < fData.end());
	// Triggers if elements have been added to the buffer while iterating entries
	SkASSERT(expectedCount == fCount);
	// Make sure the start of the entry looks like a header
	SkASSERT(this->header(entry)->fSentinel == kSentinel);
	}
	#endif

	///////////////////////////////////////////////////////////////////////////////////////////////////
	// Iterator implementations
	///////////////////////////////////////////////////////////////////////////////////////////////////

	template<typename T>
	bool GrQuadBuffer<T>::Iter::next() {
	SkASSERT(fNextEntry);
	if (fNextEntry >= fBuffer->fData.end()) {
	return false;
	}
	// There is at least one more entry, so store the current start for metadata access
	fCurrentEntry = fNextEntry;

	// And then unpack the device and optional local coordinates into fDeviceQuad and fLocalQuad
	const Header* h = fBuffer->header(fCurrentEntry);
	const float* coords = fBuffer->coords(fCurrentEntry);
	coords = fBuffer->unpackQuad(static_cast<GrQuad::Type>(h->fDeviceType), coords, &fDeviceQuad);
	if (h->fHasLocals) {
	coords = fBuffer->unpackQuad(static_cast<GrQuad::Type>(h->fLocalType), coords, &fLocalQuad);
	} // else localQuad() will return a nullptr so no need to reset fLocalQuad

	// At this point, coords points to the start of the next entry
	fNextEntry = static_cast<const char>(static_cast<const void>(coords));
	SkASSERT((fNextEntry - fCurrentEntry) == fBuffer->entrySize(h));
	return true;
	}

	template<typename T>
	bool GrQuadBuffer<T>::MetadataIter::next() {
	if (fCurrentEntry) {
	// Advance pointer by entry size
	if (fCurrentEntry < fBuffer->fData.end()) {
	const Header* h = fBuffer->header(fCurrentEntry);
	fCurrentEntry += fBuffer->entrySize(h);
	}
	} else {
	// First call to next
	fCurrentEntry = fBuffer->fData.begin();
	}
	// Nothing else is needed to do but report whether or not the updated pointer is valid
	return fCurrentEntry < fBuffer->fData.end();
	}
	#endif // GrQuadBuffer_DEFINED