src/gpu/GrBufferAllocPool.cpp - platform/external/skia - Gitiles

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */


 #include "GrBufferAllocPool.h"
 #include "GrBuffer.h"
 #include "GrCaps.h"
 #include "GrContext.h"
 #include "GrGpu.h"
 #include "GrResourceProvider.h"
 #include "GrTypes.h"

 #include "SkTraceEvent.h"

 #ifdef SK_DEBUG
     #define VALIDATE validate
 #else
     static void VALIDATE(bool = false) {}
 #endif

 static const size_t MIN_VERTEX_BUFFER_SIZE = 1 << 15;
 static const size_t MIN_INDEX_BUFFER_SIZE = 1 << 12;

 // page size
 #define GrBufferAllocPool_MIN_BLOCK_SIZE ((size_t)1 << 15)

 #define UNMAP_BUFFER(block)                                                               \
 do {                                                                                      \
     TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("skia.gpu"),                           \
                          "GrBufferAllocPool Unmapping Buffer",                            \
                          TRACE_EVENT_SCOPE_THREAD,                                        \
                          "percent_unwritten",                                             \
                          (float)((block).fBytesFree) / (block).fBuffer->gpuMemorySize()); \
     (block).fBuffer->unmap();                                                             \
 } while (false)

 GrBufferAllocPool::GrBufferAllocPool(GrGpu* gpu,
                                      GrBufferType bufferType,
                                      size_t blockSize)
     : fBlocks(8) {

     fGpu = SkRef(gpu);
     fCpuData = nullptr;
     fBufferType = bufferType;
     fBufferPtr = nullptr;
     fMinBlockSize = SkTMax(GrBufferAllocPool_MIN_BLOCK_SIZE, blockSize);

     fBytesInUse = 0;

     fBufferMapThreshold = gpu->caps()->bufferMapThreshold();
 }

 void GrBufferAllocPool::deleteBlocks() {
     if (fBlocks.count()) {
         GrBuffer* buffer = fBlocks.back().fBuffer;
         if (buffer->isMapped()) {
             UNMAP_BUFFER(fBlocks.back());
         }
     }
     while (!fBlocks.empty()) {
         this->destroyBlock();
     }
     SkASSERT(!fBufferPtr);
 }

 GrBufferAllocPool::~GrBufferAllocPool() {
     VALIDATE();
     this->deleteBlocks();
     sk_free(fCpuData);
     fGpu->unref();
 }

 void GrBufferAllocPool::reset() {
     VALIDATE();
     fBytesInUse = 0;
     this->deleteBlocks();

     // we may have created a large cpu mirror of a large VB. Reset the size to match our minimum.
     this->resetCpuData(fMinBlockSize);

     VALIDATE();
 }

 void GrBufferAllocPool::unmap() {
     VALIDATE();

     if (fBufferPtr) {
         BufferBlock& block = fBlocks.back();
         if (block.fBuffer->isMapped()) {
             UNMAP_BUFFER(block);
         } else {
             size_t flushSize = block.fBuffer->gpuMemorySize() - block.fBytesFree;
             this->flushCpuData(fBlocks.back(), flushSize);
         }
         fBufferPtr = nullptr;
     }
     VALIDATE();
 }

 #ifdef SK_DEBUG
 void GrBufferAllocPool::validate(bool unusedBlockAllowed) const {
     bool wasDestroyed = false;
     if (fBufferPtr) {
         SkASSERT(!fBlocks.empty());
         if (fBlocks.back().fBuffer->isMapped()) {
             GrBuffer* buf = fBlocks.back().fBuffer;
             SkASSERT(buf->mapPtr() == fBufferPtr);
         } else {
             SkASSERT(fCpuData == fBufferPtr);
         }
     } else {
         SkASSERT(fBlocks.empty() || !fBlocks.back().fBuffer->isMapped());
     }
     size_t bytesInUse = 0;
     for (int i = 0; i < fBlocks.count() - 1; ++i) {
         SkASSERT(!fBlocks[i].fBuffer->isMapped());
     }
     for (int i = 0; !wasDestroyed && i < fBlocks.count(); ++i) {
         if (fBlocks[i].fBuffer->wasDestroyed()) {
             wasDestroyed = true;
         } else {
             size_t bytes = fBlocks[i].fBuffer->gpuMemorySize() - fBlocks[i].fBytesFree;
             bytesInUse += bytes;
             SkASSERT(bytes || unusedBlockAllowed);
         }
     }

     if (!wasDestroyed) {
         SkASSERT(bytesInUse == fBytesInUse);
         if (unusedBlockAllowed) {
             SkASSERT((fBytesInUse && !fBlocks.empty()) ||
                      (!fBytesInUse && (fBlocks.count() < 2)));
         } else {
             SkASSERT((0 == fBytesInUse) == fBlocks.empty());
         }
     }
 }
 #endif

 void* GrBufferAllocPool::makeSpace(size_t size,
                                    size_t alignment,
                                    const GrBuffer** buffer,
                                    size_t* offset) {
     VALIDATE();

     SkASSERT(buffer);
     SkASSERT(offset);

     if (fBufferPtr) {
         BufferBlock& back = fBlocks.back();
         size_t usedBytes = back.fBuffer->gpuMemorySize() - back.fBytesFree;
         size_t pad = GrSizeAlignUpPad(usedBytes, alignment);
         if ((size + pad) <= back.fBytesFree) {
             memset((void*)(reinterpret_cast<intptr_t>(fBufferPtr) + usedBytes), 0, pad);
             usedBytes += pad;
             *offset = usedBytes;
             *buffer = back.fBuffer;
             back.fBytesFree -= size + pad;
             fBytesInUse += size + pad;
             VALIDATE();
             return (void*)(reinterpret_cast<intptr_t>(fBufferPtr) + usedBytes);
         }
     }

     // We could honor the space request using by a partial update of the current
     // VB (if there is room). But we don't currently use draw calls to GL that
     // allow the driver to know that previously issued draws won't read from
     // the part of the buffer we update. Also, the GL buffer implementation
     // may be cheating on the actual buffer size by shrinking the buffer on
     // updateData() if the amount of data passed is less than the full buffer
     // size.

     if (!this->createBlock(size)) {
         return nullptr;
     }
     SkASSERT(fBufferPtr);

     *offset = 0;
     BufferBlock& back = fBlocks.back();
     *buffer = back.fBuffer;
     back.fBytesFree -= size;
     fBytesInUse += size;
     VALIDATE();
     return fBufferPtr;
 }

 void GrBufferAllocPool::putBack(size_t bytes) {
     VALIDATE();

     while (bytes) {
         // caller shouldn't try to put back more than they've taken
         SkASSERT(!fBlocks.empty());
         BufferBlock& block = fBlocks.back();
         size_t bytesUsed = block.fBuffer->gpuMemorySize() - block.fBytesFree;
         if (bytes >= bytesUsed) {
             bytes -= bytesUsed;
             fBytesInUse -= bytesUsed;
             // if we locked a vb to satisfy the make space and we're releasing
             // beyond it, then unmap it.
             if (block.fBuffer->isMapped()) {
                 UNMAP_BUFFER(block);
             }
             this->destroyBlock();
         } else {
             block.fBytesFree += bytes;
             fBytesInUse -= bytes;
             bytes = 0;
             break;
         }
     }

     VALIDATE();
 }

 bool GrBufferAllocPool::createBlock(size_t requestSize) {

     size_t size = SkTMax(requestSize, fMinBlockSize);
     SkASSERT(size >= GrBufferAllocPool_MIN_BLOCK_SIZE);

     VALIDATE();

     BufferBlock& block = fBlocks.push_back();

     block.fBuffer = this->getBuffer(size);
     if (!block.fBuffer) {
         fBlocks.pop_back();
         return false;
     }

     block.fBytesFree = block.fBuffer->gpuMemorySize();
     if (fBufferPtr) {
         SkASSERT(fBlocks.count() > 1);
         BufferBlock& prev = fBlocks.fromBack(1);
         if (prev.fBuffer->isMapped()) {
             UNMAP_BUFFER(prev);
         } else {
             this->flushCpuData(prev, prev.fBuffer->gpuMemorySize() - prev.fBytesFree);
         }
         fBufferPtr = nullptr;
     }

     SkASSERT(!fBufferPtr);

     // If the buffer is CPU-backed we map it because it is free to do so and saves a copy.
     // Otherwise when buffer mapping is supported we map if the buffer size is greater than the
     // threshold.
     bool attemptMap = block.fBuffer->isCPUBacked();
     if (!attemptMap && GrCaps::kNone_MapFlags != fGpu->caps()->mapBufferFlags()) {
         attemptMap = size > fBufferMapThreshold;
     }

     if (attemptMap) {
         fBufferPtr = block.fBuffer->map();
     }

     if (!fBufferPtr) {
         fBufferPtr = this->resetCpuData(block.fBytesFree);
     }

     VALIDATE(true);

     return true;
 }

 void GrBufferAllocPool::destroyBlock() {
     SkASSERT(!fBlocks.empty());

     BufferBlock& block = fBlocks.back();

     SkASSERT(!block.fBuffer->isMapped());
     block.fBuffer->unref();
     fBlocks.pop_back();
     fBufferPtr = nullptr;
 }

 void* GrBufferAllocPool::resetCpuData(size_t newSize) {
     sk_free(fCpuData);
     if (newSize) {
         if (fGpu->caps()->mustClearUploadedBufferData()) {
             fCpuData = sk_calloc(newSize);
         } else {
             fCpuData = sk_malloc_throw(newSize);
         }
     } else {
         fCpuData = nullptr;
     }
     return fCpuData;
 }


 void GrBufferAllocPool::flushCpuData(const BufferBlock& block, size_t flushSize) {
     GrBuffer* buffer = block.fBuffer;
     SkASSERT(buffer);
     SkASSERT(!buffer->isMapped());
     SkASSERT(fCpuData == fBufferPtr);
     SkASSERT(flushSize <= buffer->gpuMemorySize());
     VALIDATE(true);

     if (GrCaps::kNone_MapFlags != fGpu->caps()->mapBufferFlags() &&
         flushSize > fBufferMapThreshold) {
         void* data = buffer->map();
         if (data) {
             memcpy(data, fBufferPtr, flushSize);
             UNMAP_BUFFER(block);
             return;
         }
     }
     buffer->updateData(fBufferPtr, flushSize);
     VALIDATE(true);
 }

 GrBuffer* GrBufferAllocPool::getBuffer(size_t size) {

     GrResourceProvider* rp = fGpu->getContext()->resourceProvider();

     // Shouldn't have to use this flag (https://bug.skia.org/4156)
     static const uint32_t kFlags = GrResourceProvider::kNoPendingIO_Flag;
     return rp->createBuffer(size, fBufferType, kDynamic_GrAccessPattern, kFlags);
 }

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

 GrVertexBufferAllocPool::GrVertexBufferAllocPool(GrGpu* gpu)
     : GrBufferAllocPool(gpu, kVertex_GrBufferType, MIN_VERTEX_BUFFER_SIZE) {
 }

 void* GrVertexBufferAllocPool::makeSpace(size_t vertexSize,
                                          int vertexCount,
                                          const GrBuffer** buffer,
                                          int* startVertex) {

     SkASSERT(vertexCount >= 0);
     SkASSERT(buffer);
     SkASSERT(startVertex);

     size_t offset = 0; // assign to suppress warning
     void* ptr = INHERITED::makeSpace(vertexSize * vertexCount,
                                      vertexSize,
                                      buffer,
                                      &offset);

     SkASSERT(0 == offset % vertexSize);
     *startVertex = static_cast<int>(offset / vertexSize);
     return ptr;
 }

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

 GrIndexBufferAllocPool::GrIndexBufferAllocPool(GrGpu* gpu)
     : GrBufferAllocPool(gpu, kIndex_GrBufferType, MIN_INDEX_BUFFER_SIZE) {
 }

 void* GrIndexBufferAllocPool::makeSpace(int indexCount,
                                         const GrBuffer** buffer,
                                         int* startIndex) {

     SkASSERT(indexCount >= 0);
     SkASSERT(buffer);
     SkASSERT(startIndex);

     size_t offset = 0; // assign to suppress warning
     void* ptr = INHERITED::makeSpace(indexCount * sizeof(uint16_t),
                                      sizeof(uint16_t),
                                      buffer,
                                      &offset);

     SkASSERT(0 == offset % sizeof(uint16_t));
     *startIndex = static_cast<int>(offset / sizeof(uint16_t));
     return ptr;
 }
	/*
	* Copyright 2010 Google Inc.
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/


	#include "GrBufferAllocPool.h"
	#include "GrBuffer.h"
	#include "GrCaps.h"
	#include "GrContext.h"
	#include "GrGpu.h"
	#include "GrResourceProvider.h"
	#include "GrTypes.h"

	#include "SkTraceEvent.h"

	#ifdef SK_DEBUG
	#define VALIDATE validate
	#else
	static void VALIDATE(bool = false) {}
	#endif

	static const size_t MIN_VERTEX_BUFFER_SIZE = 1 << 15;
	static const size_t MIN_INDEX_BUFFER_SIZE = 1 << 12;

	// page size
	#define GrBufferAllocPool_MIN_BLOCK_SIZE ((size_t)1 << 15)

	#define UNMAP_BUFFER(block) \
	do { \
	TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("skia.gpu"), \
	"GrBufferAllocPool Unmapping Buffer", \
	TRACE_EVENT_SCOPE_THREAD, \
	"percent_unwritten", \
	(float)((block).fBytesFree) / (block).fBuffer->gpuMemorySize()); \
	(block).fBuffer->unmap(); \
	} while (false)

	GrBufferAllocPool::GrBufferAllocPool(GrGpu* gpu,
	GrBufferType bufferType,
	size_t blockSize)
	: fBlocks(8) {

	fGpu = SkRef(gpu);
	fCpuData = nullptr;
	fBufferType = bufferType;
	fBufferPtr = nullptr;
	fMinBlockSize = SkTMax(GrBufferAllocPool_MIN_BLOCK_SIZE, blockSize);

	fBytesInUse = 0;

	fBufferMapThreshold = gpu->caps()->bufferMapThreshold();
	}

	void GrBufferAllocPool::deleteBlocks() {
	if (fBlocks.count()) {
	GrBuffer* buffer = fBlocks.back().fBuffer;
	if (buffer->isMapped()) {
	UNMAP_BUFFER(fBlocks.back());
	}
	}
	while (!fBlocks.empty()) {
	this->destroyBlock();
	}
	SkASSERT(!fBufferPtr);
	}

	GrBufferAllocPool::~GrBufferAllocPool() {
	VALIDATE();
	this->deleteBlocks();
	sk_free(fCpuData);
	fGpu->unref();
	}

	void GrBufferAllocPool::reset() {
	VALIDATE();
	fBytesInUse = 0;
	this->deleteBlocks();

	// we may have created a large cpu mirror of a large VB. Reset the size to match our minimum.
	this->resetCpuData(fMinBlockSize);

	VALIDATE();
	}

	void GrBufferAllocPool::unmap() {
	VALIDATE();

	if (fBufferPtr) {
	BufferBlock& block = fBlocks.back();
	if (block.fBuffer->isMapped()) {
	UNMAP_BUFFER(block);
	} else {
	size_t flushSize = block.fBuffer->gpuMemorySize() - block.fBytesFree;
	this->flushCpuData(fBlocks.back(), flushSize);
	}
	fBufferPtr = nullptr;
	}
	VALIDATE();
	}

	#ifdef SK_DEBUG
	void GrBufferAllocPool::validate(bool unusedBlockAllowed) const {
	bool wasDestroyed = false;
	if (fBufferPtr) {
	SkASSERT(!fBlocks.empty());
	if (fBlocks.back().fBuffer->isMapped()) {
	GrBuffer* buf = fBlocks.back().fBuffer;
	SkASSERT(buf->mapPtr() == fBufferPtr);
	} else {
	SkASSERT(fCpuData == fBufferPtr);
	}
	} else {
	SkASSERT(fBlocks.empty() \|\| !fBlocks.back().fBuffer->isMapped());
	}
	size_t bytesInUse = 0;
	for (int i = 0; i < fBlocks.count() - 1; ++i) {
	SkASSERT(!fBlocks[i].fBuffer->isMapped());
	}
	for (int i = 0; !wasDestroyed && i < fBlocks.count(); ++i) {
	if (fBlocks[i].fBuffer->wasDestroyed()) {
	wasDestroyed = true;
	} else {
	size_t bytes = fBlocks[i].fBuffer->gpuMemorySize() - fBlocks[i].fBytesFree;
	bytesInUse += bytes;
	SkASSERT(bytes \|\| unusedBlockAllowed);
	}
	}

	if (!wasDestroyed) {
	SkASSERT(bytesInUse == fBytesInUse);
	if (unusedBlockAllowed) {
	SkASSERT((fBytesInUse && !fBlocks.empty()) \|\|
	(!fBytesInUse && (fBlocks.count() < 2)));
	} else {
	SkASSERT((0 == fBytesInUse) == fBlocks.empty());
	}
	}
	}
	#endif

	void* GrBufferAllocPool::makeSpace(size_t size,
	size_t alignment,
	const GrBuffer** buffer,
	size_t* offset) {
	VALIDATE();

	SkASSERT(buffer);
	SkASSERT(offset);

	if (fBufferPtr) {
	BufferBlock& back = fBlocks.back();
	size_t usedBytes = back.fBuffer->gpuMemorySize() - back.fBytesFree;
	size_t pad = GrSizeAlignUpPad(usedBytes, alignment);
	if ((size + pad) <= back.fBytesFree) {
	memset((void*)(reinterpret_cast<intptr_t>(fBufferPtr) + usedBytes), 0, pad);
	usedBytes += pad;
	*offset = usedBytes;
	*buffer = back.fBuffer;
	back.fBytesFree -= size + pad;
	fBytesInUse += size + pad;
	VALIDATE();
	return (void*)(reinterpret_cast<intptr_t>(fBufferPtr) + usedBytes);
	}
	}

	// We could honor the space request using by a partial update of the current
	// VB (if there is room). But we don't currently use draw calls to GL that
	// allow the driver to know that previously issued draws won't read from
	// the part of the buffer we update. Also, the GL buffer implementation
	// may be cheating on the actual buffer size by shrinking the buffer on
	// updateData() if the amount of data passed is less than the full buffer
	// size.

	if (!this->createBlock(size)) {
	return nullptr;
	}
	SkASSERT(fBufferPtr);

	*offset = 0;
	BufferBlock& back = fBlocks.back();
	*buffer = back.fBuffer;
	back.fBytesFree -= size;
	fBytesInUse += size;
	VALIDATE();
	return fBufferPtr;
	}

	void GrBufferAllocPool::putBack(size_t bytes) {
	VALIDATE();

	while (bytes) {
	// caller shouldn't try to put back more than they've taken
	SkASSERT(!fBlocks.empty());
	BufferBlock& block = fBlocks.back();
	size_t bytesUsed = block.fBuffer->gpuMemorySize() - block.fBytesFree;
	if (bytes >= bytesUsed) {
	bytes -= bytesUsed;
	fBytesInUse -= bytesUsed;
	// if we locked a vb to satisfy the make space and we're releasing
	// beyond it, then unmap it.
	if (block.fBuffer->isMapped()) {
	UNMAP_BUFFER(block);
	}
	this->destroyBlock();
	} else {
	block.fBytesFree += bytes;
	fBytesInUse -= bytes;
	bytes = 0;
	break;
	}
	}

	VALIDATE();
	}

	bool GrBufferAllocPool::createBlock(size_t requestSize) {

	size_t size = SkTMax(requestSize, fMinBlockSize);
	SkASSERT(size >= GrBufferAllocPool_MIN_BLOCK_SIZE);

	VALIDATE();

	BufferBlock& block = fBlocks.push_back();

	block.fBuffer = this->getBuffer(size);
	if (!block.fBuffer) {
	fBlocks.pop_back();
	return false;
	}

	block.fBytesFree = block.fBuffer->gpuMemorySize();
	if (fBufferPtr) {
	SkASSERT(fBlocks.count() > 1);
	BufferBlock& prev = fBlocks.fromBack(1);
	if (prev.fBuffer->isMapped()) {
	UNMAP_BUFFER(prev);
	} else {
	this->flushCpuData(prev, prev.fBuffer->gpuMemorySize() - prev.fBytesFree);
	}
	fBufferPtr = nullptr;
	}

	SkASSERT(!fBufferPtr);

	// If the buffer is CPU-backed we map it because it is free to do so and saves a copy.
	// Otherwise when buffer mapping is supported we map if the buffer size is greater than the
	// threshold.
	bool attemptMap = block.fBuffer->isCPUBacked();
	if (!attemptMap && GrCaps::kNone_MapFlags != fGpu->caps()->mapBufferFlags()) {
	attemptMap = size > fBufferMapThreshold;
	}

	if (attemptMap) {
	fBufferPtr = block.fBuffer->map();
	}

	if (!fBufferPtr) {
	fBufferPtr = this->resetCpuData(block.fBytesFree);
	}

	VALIDATE(true);

	return true;
	}

	void GrBufferAllocPool::destroyBlock() {
	SkASSERT(!fBlocks.empty());

	BufferBlock& block = fBlocks.back();

	SkASSERT(!block.fBuffer->isMapped());
	block.fBuffer->unref();
	fBlocks.pop_back();
	fBufferPtr = nullptr;
	}

	void* GrBufferAllocPool::resetCpuData(size_t newSize) {
	sk_free(fCpuData);
	if (newSize) {
	if (fGpu->caps()->mustClearUploadedBufferData()) {
	fCpuData = sk_calloc(newSize);
	} else {
	fCpuData = sk_malloc_throw(newSize);
	}
	} else {
	fCpuData = nullptr;
	}
	return fCpuData;
	}


	void GrBufferAllocPool::flushCpuData(const BufferBlock& block, size_t flushSize) {
	GrBuffer* buffer = block.fBuffer;
	SkASSERT(buffer);
	SkASSERT(!buffer->isMapped());
	SkASSERT(fCpuData == fBufferPtr);
	SkASSERT(flushSize <= buffer->gpuMemorySize());
	VALIDATE(true);

	if (GrCaps::kNone_MapFlags != fGpu->caps()->mapBufferFlags() &&
	flushSize > fBufferMapThreshold) {
	void* data = buffer->map();
	if (data) {
	memcpy(data, fBufferPtr, flushSize);
	UNMAP_BUFFER(block);
	return;
	}
	}
	buffer->updateData(fBufferPtr, flushSize);
	VALIDATE(true);
	}

	GrBuffer* GrBufferAllocPool::getBuffer(size_t size) {

	GrResourceProvider* rp = fGpu->getContext()->resourceProvider();

	// Shouldn't have to use this flag (https://bug.skia.org/4156)
	static const uint32_t kFlags = GrResourceProvider::kNoPendingIO_Flag;
	return rp->createBuffer(size, fBufferType, kDynamic_GrAccessPattern, kFlags);
	}

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

	GrVertexBufferAllocPool::GrVertexBufferAllocPool(GrGpu* gpu)
	: GrBufferAllocPool(gpu, kVertex_GrBufferType, MIN_VERTEX_BUFFER_SIZE) {
	}

	void* GrVertexBufferAllocPool::makeSpace(size_t vertexSize,
	int vertexCount,
	const GrBuffer** buffer,
	int* startVertex) {

	SkASSERT(vertexCount >= 0);
	SkASSERT(buffer);
	SkASSERT(startVertex);

	size_t offset = 0; // assign to suppress warning
	void* ptr = INHERITED::makeSpace(vertexSize * vertexCount,
	vertexSize,
	buffer,
	&offset);

	SkASSERT(0 == offset % vertexSize);
	*startVertex = static_cast<int>(offset / vertexSize);
	return ptr;
	}

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

	GrIndexBufferAllocPool::GrIndexBufferAllocPool(GrGpu* gpu)
	: GrBufferAllocPool(gpu, kIndex_GrBufferType, MIN_INDEX_BUFFER_SIZE) {
	}

	void* GrIndexBufferAllocPool::makeSpace(int indexCount,
	const GrBuffer** buffer,
	int* startIndex) {

	SkASSERT(indexCount >= 0);
	SkASSERT(buffer);
	SkASSERT(startIndex);

	size_t offset = 0; // assign to suppress warning
	void* ptr = INHERITED::makeSpace(indexCount * sizeof(uint16_t),
	sizeof(uint16_t),
	buffer,
	&offset);

	SkASSERT(0 == offset % sizeof(uint16_t));
	*startIndex = static_cast<int>(offset / sizeof(uint16_t));
	return ptr;
	}