src/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

   1 /*
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   6  * are met:
   7  *
   8  * 1.  Redistributions of source code must retain the above copyright
   9  *     notice, this list of conditions and the following disclaimer.
  10  * 2.  Redistributions in binary form must reproduce the above copyright
  11  *     notice, this list of conditions and the following disclaimer in the
  12  *     documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  15  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  17  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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  25
  26 #include "config.h"
  27
  28 #include "platform/graphics/Canvas2DLayerBridge.h"
  29
  30 #include "GrContext.h"
  31 #include "SkDevice.h"
  32 #include "SkSurface.h"
  33 #include "platform/TraceEvent.h"
  34 #include "platform/graphics/Canvas2DLayerManager.h"
  35 #include "platform/graphics/GraphicsLayer.h"
  36 #include "public/platform/Platform.h"
  37 #include "public/platform/WebCompositorSupport.h"
  38 #include "public/platform/WebGraphicsContext3D.h"
  39 #include "public/platform/WebGraphicsContext3DProvider.h"
  40 #include "wtf/RefCountedLeakCounter.h"
  41
  42 namespace {
  43 enum {
  44     InvalidMailboxIndex = -1,
  45 };
  46
  47 DEFINE_DEBUG_ONLY_GLOBAL(WTF::RefCountedLeakCounter, canvas2DLayerBridgeInstanceCounter, ("Canvas2DLayerBridge"));
  48 }
  49
  50 namespace blink {
  51
  52 static PassRefPtr<SkSurface> createSkSurface(GrContext* gr, const IntSize& size, int msaaSampleCount = 0)
  53 {
  54     if (!gr)
  55         return nullptr;
  56     gr->resetContext();
  57     SkImageInfo info = SkImageInfo::MakeN32Premul(size.width(), size.height());
  58     return adoptRef(SkSurface::NewRenderTarget(gr, info,  msaaSampleCount));
  59 }
  60
  61 PassRefPtr<Canvas2DLayerBridge> Canvas2DLayerBridge::create(const IntSize& size, OpacityMode opacityMode, int msaaSampleCount)
  62 {
  63     TRACE_EVENT_INSTANT0("test_gpu", "Canvas2DLayerBridgeCreation");
  64     OwnPtr<WebGraphicsContext3DProvider> contextProvider = adoptPtr(Platform::current()->createSharedOffscreenGraphicsContext3DProvider());
  65     if (!contextProvider)
  66         return nullptr;
  67     RefPtr<SkSurface> surface(createSkSurface(contextProvider->grContext(), size, msaaSampleCount));
  68     if (!surface)
  69         return nullptr;
  70     RefPtr<Canvas2DLayerBridge> layerBridge;
  71     OwnPtr<SkDeferredCanvas> canvas = adoptPtr(SkDeferredCanvas::Create(surface.get()));
  72     layerBridge = adoptRef(new Canvas2DLayerBridge(contextProvider.release(), canvas.release(), surface.release(), msaaSampleCount, opacityMode));
  73     return layerBridge.release();
  74 }
  75
  76 Canvas2DLayerBridge::Canvas2DLayerBridge(PassOwnPtr<WebGraphicsContext3DProvider> contextProvider, PassOwnPtr<SkDeferredCanvas> canvas, PassRefPtr<SkSurface> surface, int msaaSampleCount, OpacityMode opacityMode)
  77     : m_canvas(canvas)
  78     , m_surface(surface)
  79     , m_contextProvider(contextProvider)
  80     , m_imageBuffer(0)
  81     , m_msaaSampleCount(msaaSampleCount)
  82     , m_bytesAllocated(0)
  83     , m_didRecordDrawCommand(false)
  84     , m_isSurfaceValid(true)
  85     , m_framesPending(0)
  86     , m_framesSinceMailboxRelease(0)
  87     , m_destructionInProgress(false)
  88     , m_rateLimitingEnabled(false)
  89     , m_isHidden(false)
  90     , m_next(0)
  91     , m_prev(0)
  92     , m_lastImageId(0)
  93     , m_releasedMailboxInfoIndex(InvalidMailboxIndex)
  94 {
  95     ASSERT(m_canvas);
  96     ASSERT(m_surface);
  97     ASSERT(m_contextProvider);
  98     // Used by browser tests to detect the use of a Canvas2DLayerBridge.
  99     TRACE_EVENT_INSTANT0("test_gpu", "Canvas2DLayerBridgeCreation");
 100     m_layer = adoptPtr(Platform::current()->compositorSupport()->createExternalTextureLayer(this));
 101     m_layer->setOpaque(opacityMode == Opaque);
 102     m_layer->setBlendBackgroundColor(opacityMode != Opaque);
 103     GraphicsLayer::registerContentsLayer(m_layer->layer());
 104     m_layer->setRateLimitContext(m_rateLimitingEnabled);
 105     m_canvas->setNotificationClient(this);
 106 #ifndef NDEBUG
 107     canvas2DLayerBridgeInstanceCounter.increment();
 108 #endif
 109 }
 110
 111 Canvas2DLayerBridge::~Canvas2DLayerBridge()
 112 {
 113     ASSERT(m_destructionInProgress);
 114     ASSERT(!Canvas2DLayerManager::get().isInList(this));
 115     m_layer.clear();
 116     freeReleasedMailbox();
 117 #if ENABLE(ASSERT)
 118     Vector<MailboxInfo>::iterator mailboxInfo;
 119     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); ++mailboxInfo) {
 120         ASSERT(mailboxInfo->m_status != MailboxInUse);
 121         ASSERT(mailboxInfo->m_status != MailboxReleased || m_contextProvider->context3d()->isContextLost() || !m_isSurfaceValid);
 122     }
 123 #endif
 124     m_mailboxes.clear();
 125 #ifndef NDEBUG
 126     canvas2DLayerBridgeInstanceCounter.decrement();
 127 #endif
 128 }
 129
 130 void Canvas2DLayerBridge::beginDestruction()
 131 {
 132     ASSERT(!m_destructionInProgress);
 133     setRateLimitingEnabled(false);
 134     m_canvas->silentFlush();
 135     m_imageBuffer = 0;
 136     freeTransientResources();
 137     setIsHidden(true);
 138     m_destructionInProgress = true;
 139     GraphicsLayer::unregisterContentsLayer(m_layer->layer());
 140     m_canvas->setNotificationClient(0);
 141     m_surface.clear();
 142     m_canvas.clear();
 143     m_layer->clearTexture();
 144     // Orphaning the layer is required to trigger the recration of a new layer
 145     // in the case where destruction is caused by a canvas resize. Test:
 146     // virtual/gpu/fast/canvas/canvas-resize-after-paint-without-layout.html
 147     m_layer->layer()->removeFromParent();
 148     // To anyone who ever hits this assert: Please update crbug.com/344666
 149     // with repro steps.
 150     ASSERT(!m_bytesAllocated);
 151 }
 152
 153 void Canvas2DLayerBridge::setIsHidden(bool hidden)
 154 {
 155     ASSERT(!m_destructionInProgress);
 156     bool newHiddenValue = hidden || m_destructionInProgress;
 157     if (m_isHidden == newHiddenValue)
 158         return;
 159
 160     m_isHidden = newHiddenValue;
 161     if (isHidden()) {
 162         freeTransientResources();
 163     }
 164 }
 165
 166 void Canvas2DLayerBridge::willAccessPixels()
 167 {
 168     // A readback operation may alter the texture parameters, which may affect
 169     // the compositor's behavior. Therefore, we must trigger copy-on-write
 170     // even though we are not technically writing to the texture, only to its
 171     // parameters.
 172     m_surface->notifyContentWillChange(SkSurface::kRetain_ContentChangeMode);
 173 }
 174
 175 void Canvas2DLayerBridge::freeTransientResources()
 176 {
 177     ASSERT(!m_destructionInProgress);
 178     if (!m_isSurfaceValid)
 179         return;
 180     freeReleasedMailbox();
 181     flush();
 182     freeMemoryIfPossible(bytesAllocated());
 183     ASSERT(!hasTransientResources());
 184 }
 185
 186 bool Canvas2DLayerBridge::hasTransientResources() const
 187 {
 188     return !m_destructionInProgress && (hasReleasedMailbox() || bytesAllocated());
 189 }
 190
 191 void Canvas2DLayerBridge::limitPendingFrames()
 192 {
 193     ASSERT(!m_destructionInProgress);
 194     if (isHidden()) {
 195         freeTransientResources();
 196         return;
 197     }
 198     if (m_didRecordDrawCommand) {
 199         m_framesPending++;
 200         m_didRecordDrawCommand = false;
 201         if (m_framesPending > 1) {
 202             // Turn on the rate limiter if this layer tends to accumulate a
 203             // non-discardable multi-frame backlog of draw commands.
 204             setRateLimitingEnabled(true);
 205         }
 206         if (m_rateLimitingEnabled) {
 207             flush();
 208         }
 209     }
 210     ++m_framesSinceMailboxRelease;
 211     if (releasedMailboxHasExpired()) {
 212         freeReleasedMailbox();
 213     }
 214 }
 215
 216 void Canvas2DLayerBridge::prepareForDraw()
 217 {
 218     ASSERT(!m_destructionInProgress);
 219     ASSERT(m_layer);
 220     if (!checkSurfaceValid()) {
 221         if (m_canvas) {
 222             // drop pending commands because there is no surface to draw to
 223             m_canvas->silentFlush();
 224         }
 225         return;
 226     }
 227     context()->makeContextCurrent();
 228 }
 229
 230 void Canvas2DLayerBridge::storageAllocatedForRecordingChanged(size_t bytesAllocated)
 231 {
 232     ASSERT(!m_destructionInProgress);
 233     intptr_t delta = (intptr_t)bytesAllocated - (intptr_t)m_bytesAllocated;
 234     m_bytesAllocated = bytesAllocated;
 235     Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this, delta);
 236 }
 237
 238 size_t Canvas2DLayerBridge::storageAllocatedForRecording()
 239 {
 240     return m_canvas->storageAllocatedForRecording();
 241 }
 242
 243 void Canvas2DLayerBridge::flushedDrawCommands()
 244 {
 245     ASSERT(!m_destructionInProgress);
 246     storageAllocatedForRecordingChanged(storageAllocatedForRecording());
 247     m_framesPending = 0;
 248 }
 249
 250 void Canvas2DLayerBridge::skippedPendingDrawCommands()
 251 {
 252     ASSERT(!m_destructionInProgress);
 253     // Stop triggering the rate limiter if SkDeferredCanvas is detecting
 254     // and optimizing overdraw.
 255     setRateLimitingEnabled(false);
 256     flushedDrawCommands();
 257 }
 258
 259 void Canvas2DLayerBridge::setRateLimitingEnabled(bool enabled)
 260 {
 261     ASSERT(!m_destructionInProgress);
 262     if (m_rateLimitingEnabled != enabled) {
 263         m_rateLimitingEnabled = enabled;
 264         m_layer->setRateLimitContext(m_rateLimitingEnabled);
 265     }
 266 }
 267
 268 size_t Canvas2DLayerBridge::freeMemoryIfPossible(size_t bytesToFree)
 269 {
 270     ASSERT(!m_destructionInProgress);
 271     size_t bytesFreed = m_canvas->freeMemoryIfPossible(bytesToFree);
 272     m_bytesAllocated -= bytesFreed;
 273     if (bytesFreed)
 274         Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this, -((intptr_t)bytesFreed));
 275     return bytesFreed;
 276 }
 277
 278 void Canvas2DLayerBridge::flush()
 279 {
 280     ASSERT(!m_destructionInProgress);
 281     if (m_canvas->hasPendingCommands()) {
 282         TRACE_EVENT0("cc", "Canvas2DLayerBridge::flush");
 283         freeReleasedMailbox(); // To avoid unnecessary triple-buffering
 284         m_canvas->flush();
 285     }
 286 }
 287
 288 bool Canvas2DLayerBridge::releasedMailboxHasExpired()
 289 {
 290     // This heuristic indicates that the canvas is not being
 291     // actively presented by the compositor (3 frames rendered since
 292     // last mailbox release), suggesting that double buffering is not required.
 293     return hasReleasedMailbox() && m_framesSinceMailboxRelease > 2;
 294 }
 295
 296 Canvas2DLayerBridge::MailboxInfo* Canvas2DLayerBridge::releasedMailboxInfo()
 297 {
 298     return hasReleasedMailbox() ? &m_mailboxes[m_releasedMailboxInfoIndex] : 0;
 299 }
 300
 301 bool Canvas2DLayerBridge::hasReleasedMailbox() const
 302 {
 303     return m_releasedMailboxInfoIndex != InvalidMailboxIndex;
 304 }
 305
 306 void Canvas2DLayerBridge::freeReleasedMailbox()
 307 {
 308     if (!m_isSurfaceValid || m_contextProvider->context3d()->isContextLost())
 309         return;
 310     MailboxInfo* mailboxInfo = releasedMailboxInfo();
 311     if (!mailboxInfo)
 312         return;
 313
 314     ASSERT(mailboxInfo->m_status == MailboxReleased);
 315     if (mailboxInfo->m_mailbox.syncPoint) {
 316         context()->waitSyncPoint(mailboxInfo->m_mailbox.syncPoint);
 317         mailboxInfo->m_mailbox.syncPoint = 0;
 318     }
 319     // Invalidate texture state in case the compositor altered it since the copy-on-write.
 320     if (mailboxInfo->m_image) {
 321         if (isHidden() || releasedMailboxHasExpired())
 322             mailboxInfo->m_image->getTexture()->resetFlag(static_cast<GrTextureFlags>(GrTexture::kReturnToCache_FlagBit));
 323         mailboxInfo->m_image->getTexture()->textureParamsModified();
 324         mailboxInfo->m_image.clear();
 325     }
 326     mailboxInfo->m_status = MailboxAvailable;
 327     m_releasedMailboxInfoIndex = InvalidMailboxIndex;
 328     Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this);
 329 }
 330
 331 WebGraphicsContext3D* Canvas2DLayerBridge::context()
 332 {
 333     // Check on m_layer is necessary because context() may be called during
 334     // the destruction of m_layer
 335     if (m_layer && !m_destructionInProgress)
 336         checkSurfaceValid(); // To ensure rate limiter is disabled if context is lost.
 337     return m_contextProvider ? m_contextProvider->context3d() : 0;
 338 }
 339
 340 bool Canvas2DLayerBridge::checkSurfaceValid()
 341 {
 342     ASSERT(!m_destructionInProgress);
 343     if (m_destructionInProgress || !m_isSurfaceValid)
 344         return false;
 345     if (m_contextProvider->context3d()->isContextLost()) {
 346         m_isSurfaceValid = false;
 347         m_surface.clear();
 348         if (m_imageBuffer)
 349             m_imageBuffer->notifySurfaceInvalid();
 350         setRateLimitingEnabled(false);
 351     }
 352     return m_isSurfaceValid;
 353 }
 354
 355 bool Canvas2DLayerBridge::restoreSurface()
 356 {
 357     ASSERT(!m_destructionInProgress);
 358     if (m_destructionInProgress)
 359         return false;
 360     ASSERT(m_layer && !m_isSurfaceValid);
 361
 362     WebGraphicsContext3D* sharedContext = 0;
 363     // We must clear the mailboxes before calling m_layer->clearTexture() to prevent
 364     // re-entry via mailboxReleased from operating on defunct GrContext objects.
 365     m_mailboxes.clear();
 366     m_releasedMailboxInfoIndex = InvalidMailboxIndex;
 367     m_layer->clearTexture();
 368     m_contextProvider = adoptPtr(Platform::current()->createSharedOffscreenGraphicsContext3DProvider());
 369     if (m_contextProvider)
 370         sharedContext = m_contextProvider->context3d();
 371
 372     if (sharedContext && !sharedContext->isContextLost()) {
 373         IntSize size(m_canvas->getTopDevice()->width(), m_canvas->getTopDevice()->height());
 374         RefPtr<SkSurface> surface(createSkSurface(m_contextProvider->grContext(), size, m_msaaSampleCount));
 375         if (surface.get()) {
 376             m_surface = surface.release();
 377             m_canvas->setSurface(m_surface.get());
 378             m_isSurfaceValid = true;
 379             // FIXME: draw sad canvas picture into new buffer crbug.com/243842
 380         }
 381     }
 382
 383     return m_isSurfaceValid;
 384 }
 385
 386 bool Canvas2DLayerBridge::prepareMailbox(WebExternalTextureMailbox* outMailbox, WebExternalBitmap* bitmap)
 387 {
 388     if (m_destructionInProgress) {
 389         // It can be hit in the following sequence.
 390         // 1. Canvas draws something.
 391         // 2. The compositor begins the frame.
 392         // 3. Javascript makes a context be lost.
 393         // 4. Here.
 394         return false;
 395     }
 396     if (bitmap) {
 397         // Using accelerated 2d canvas with software renderer, which
 398         // should only happen in tests that use fake graphics contexts
 399         // or in Android WebView in software mode. In this case, we do
 400         // not care about producing any results for this canvas.
 401         m_canvas->silentFlush();
 402         m_lastImageId = 0;
 403         return false;
 404     }
 405     if (!checkSurfaceValid())
 406         return false;
 407
 408     WebGraphicsContext3D* webContext = context();
 409
 410     // Release to skia textures that were previouosly released by the
 411     // compositor. We do this before acquiring the next snapshot in
 412     // order to cap maximum gpu memory consumption.
 413     webContext->makeContextCurrent();
 414     flush();
 415
 416     RefPtr<SkImage> image = adoptRef(m_canvas->newImageSnapshot());
 417
 418     // Early exit if canvas was not drawn to since last prepareMailbox
 419     if (image->uniqueID() == m_lastImageId)
 420         return false;
 421     m_lastImageId = image->uniqueID();
 422
 423     MailboxInfo* mailboxInfo = createMailboxInfo();
 424     mailboxInfo->m_status = MailboxInUse;
 425     mailboxInfo->m_image = image;
 426
 427     ASSERT(mailboxInfo->m_mailbox.syncPoint == 0);
 428     ASSERT(mailboxInfo->m_image.get());
 429
 430     // set m_parentLayerBridge to make sure 'this' stays alive as long as it has
 431     // live mailboxes
 432     ASSERT(!mailboxInfo->m_parentLayerBridge);
 433     mailboxInfo->m_parentLayerBridge = this;
 434     *outMailbox = mailboxInfo->m_mailbox;
 435
 436     GrContext* grContext = m_contextProvider->grContext();
 437     if (!grContext)
 438         return true; // for testing: skip gl stuff when using a mock graphics context.
 439
 440     ASSERT(mailboxInfo->m_image->getTexture());
 441
 442     // Because of texture sharing with the compositor, we must invalidate
 443     // the state cached in skia so that the deferred copy on write
 444     // in SkSurface_Gpu does not make any false assumptions.
 445     mailboxInfo->m_image->getTexture()->textureParamsModified();
 446
 447     webContext->bindTexture(GL_TEXTURE_2D, mailboxInfo->m_image->getTexture()->getTextureHandle());
 448     webContext->texParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 449     webContext->texParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 450     webContext->texParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 451     webContext->texParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 452     webContext->produceTextureCHROMIUM(GL_TEXTURE_2D, mailboxInfo->m_mailbox.name);
 453     if (isHidden()) {
 454         // With hidden canvases, we release the SkImage immediately because
 455         // there is no need for animations to be double buffered.
 456         mailboxInfo->m_image.clear();
 457     } else {
 458         webContext->flush();
 459         mailboxInfo->m_mailbox.syncPoint = webContext->insertSyncPoint();
 460     }
 461     webContext->bindTexture(GL_TEXTURE_2D, 0);
 462     // Because we are changing the texture binding without going through skia,
 463     // we must dirty the context.
 464     grContext->resetContext(kTextureBinding_GrGLBackendState);
 465
 466     return true;
 467 }
 468
 469 Canvas2DLayerBridge::MailboxInfo* Canvas2DLayerBridge::createMailboxInfo() {
 470     ASSERT(!m_destructionInProgress);
 471     MailboxInfo* mailboxInfo;
 472     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); mailboxInfo++) {
 473         if (mailboxInfo->m_status == MailboxAvailable) {
 474             return mailboxInfo;
 475         }
 476     }
 477
 478     // No available mailbox: create one.
 479     m_mailboxes.grow(m_mailboxes.size() + 1);
 480     mailboxInfo = &m_mailboxes.last();
 481     context()->genMailboxCHROMIUM(mailboxInfo->m_mailbox.name);
 482     // Worst case, canvas is triple buffered.  More than 3 active mailboxes
 483     // means there is a problem.
 484     // For the single-threaded case, this value needs to be at least
 485     // kMaxSwapBuffersPending+1 (in render_widget.h).
 486     // Because of crbug.com/247874, it needs to be kMaxSwapBuffersPending+2.
 487     // TODO(piman): fix this.
 488     ASSERT(m_mailboxes.size() <= 4);
 489     ASSERT(mailboxInfo < m_mailboxes.end());
 490     return mailboxInfo;
 491 }
 492
 493 void Canvas2DLayerBridge::mailboxReleased(const WebExternalTextureMailbox& mailbox, bool lostResource)
 494 {
 495     freeReleasedMailbox(); // Never have more than one mailbox in the released state.
 496     bool contextLost = !m_isSurfaceValid || m_contextProvider->context3d()->isContextLost();
 497     Vector<MailboxInfo>::iterator mailboxInfo;
 498     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); ++mailboxInfo) {
 499         if (nameEquals(mailboxInfo->m_mailbox, mailbox)) {
 500             mailboxInfo->m_mailbox.syncPoint = mailbox.syncPoint;
 501             ASSERT(mailboxInfo->m_status == MailboxInUse);
 502             ASSERT(mailboxInfo->m_parentLayerBridge.get() == this);
 503
 504             if (contextLost) {
 505                 // No need to clean up the mailbox resource, but make sure the
 506                 // mailbox can also be reusable once the context is restored.
 507                 mailboxInfo->m_status = MailboxAvailable;
 508                 m_releasedMailboxInfoIndex = InvalidMailboxIndex;
 509                 Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this);
 510             } else if (lostResource) {
 511                 // In case of the resource is lost, we need to delete the backing
 512                 // texture and remove the mailbox from list to avoid reusing it
 513                 // in future.
 514                 if (mailboxInfo->m_image) {
 515                     GrTexture* texture = mailboxInfo->m_image->getTexture();
 516                     if (texture) {
 517                         texture->resetFlag(static_cast<GrTextureFlags>(GrTexture::kReturnToCache_FlagBit));
 518                         texture->textureParamsModified();
 519                     }
 520                     mailboxInfo->m_image.clear();
 521                 }
 522                 if (m_destructionInProgress) {
 523                     mailboxInfo->m_status = MailboxAvailable; // To satisfy assert in destructor
 524
 525                     // The following line may trigger self destruction. We do not care about
 526                     // not cleaning up m_mailboxes during destruction sequence because
 527                     // mailboxes will not be recycled after this point. Calling remove()
 528                     // could trigger a memory use after free, so we just clear the self
 529                     // reference to be safe, and we let the Canvas2DLayerBridge destructor
 530                     // take care of freeing m_mailboxes.
 531                     mailboxInfo->m_parentLayerBridge.clear();
 532                 } else {
 533                     size_t i = mailboxInfo - m_mailboxes.begin();
 534                     m_mailboxes.remove(i); // indirectly clears mailboxInfo->m_parentLayerBridge
 535                     Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this);
 536                 }
 537                 // mailboxInfo is not valid from this point, so we return immediately.
 538                 return;
 539             } else {
 540                 mailboxInfo->m_status = MailboxReleased;
 541                 m_releasedMailboxInfoIndex = mailboxInfo - m_mailboxes.begin();
 542                 m_framesSinceMailboxRelease = 0;
 543                 if (isHidden()) {
 544                     freeReleasedMailbox();
 545                 } else {
 546                     ASSERT(!m_destructionInProgress);
 547                     Canvas2DLayerManager::get().layerTransientResourceAllocationChanged(this);
 548                 }
 549             }
 550             // Trigger Canvas2DLayerBridge self-destruction if this is the
 551             // last live mailbox and the layer bridge is not externally
 552             // referenced.
 553             mailboxInfo->m_parentLayerBridge.clear();
 554             return;
 555         }
 556     }
 557 }
 558
 559 WebLayer* Canvas2DLayerBridge::layer() const
 560 {
 561     ASSERT(!m_destructionInProgress);
 562     ASSERT(m_layer);
 563     return m_layer->layer();
 564 }
 565
 566 void Canvas2DLayerBridge::finalizeFrame(const FloatRect &dirtyRect)
 567 {
 568     ASSERT(!m_destructionInProgress);
 569     Canvas2DLayerManager::get().layerDidDraw(this);
 570     m_layer->layer()->invalidateRect(dirtyRect);
 571     m_didRecordDrawCommand = true;
 572 }
 573
 574 Platform3DObject Canvas2DLayerBridge::getBackingTexture()
 575 {
 576     ASSERT(!m_destructionInProgress);
 577     if (!checkSurfaceValid())
 578         return 0;
 579     m_canvas->flush();
 580     context()->flush();
 581     GrRenderTarget* renderTarget = m_canvas->getTopDevice()->accessRenderTarget();
 582     if (renderTarget) {
 583         return renderTarget->asTexture()->getTextureHandle();
 584     }
 585     return 0;
 586 }
 587
 588 Canvas2DLayerBridge::MailboxInfo::MailboxInfo(const MailboxInfo& other) {
 589     // This copy constructor should only be used for Vector reallocation
 590     // Assuming 'other' is to be destroyed, we transfer m_image and
 591     // m_parentLayerBridge ownership rather than do a refcount dance.
 592     memcpy(&m_mailbox, &other.m_mailbox, sizeof(m_mailbox));
 593     m_image = const_cast<MailboxInfo*>(&other)->m_image.release();
 594     m_parentLayerBridge = const_cast<MailboxInfo*>(&other)->m_parentLayerBridge.release();
 595     m_status = other.m_status;
 596 }
 597
 598 } // namespace blink