content/html/content/src/nsHTMLCanvasElement.cpp
author Robert O'Callahan <robert@ocallahan.org>
Mon, 28 Mar 2011 12:59:47 +1300
changeset 63981 d9c2c2e76a37a8f6f5c337e7a445dd4a9ec4d197
parent 63873 873390caf174749f8efe0ba26a4e183e5c8049a9
child 64162 8c373f9e40569a81d1f8c34a73c3fd8e86814fa8
child 64432 a5440993101cabc2810122acf28e0962f72e9623
permissions -rw-r--r--
Bug 622072. Part 3: Support empty transactions for canvas layers. r=tnikkel The basic idea is that whenever a layer transaction updates the window, we clear out the invalidation state for the canvas rendering context, using a DidTransactionCallback registered on the layer(s) for the canvas, which calls MakeContextClean. The DidTransactionCallbacks are directed to the user data attached to the Layer, which holds a strong reference to the canvas element. This ensures that the element lives as long as the layer. Layers are destroyed when the presentation is torn down (including if the frame is destroyed), so we can't have a leak here. The reference to the canvas element is only strong because the layer might briefly outlive the frame (the layer won't be destroyed until the next paint of the window). This patch moves responsibility for calling CanvasLayer::Updated and nsFrame::MarkLayersActive from the canvas context to nsHTMLCanvasElement::InvalidateFrame. We call Updated on the retained CanvasLayer, if there is one; any other CanvasLayers created for this canvas would only be used once, and have Updated called on them in BuildLayer when created.

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is
 *   Vladimir Vukicevic <vladimir@pobox.com>
 * Portions created by the Initial Developer are Copyright (C) 2005
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#include "nsHTMLCanvasElement.h"

#include "plbase64.h"
#include "nsNetUtil.h"
#include "prmem.h"
#include "nsDOMFile.h"
#include "CheckedInt.h"

#include "nsIScriptSecurityManager.h"
#include "nsIXPConnect.h"
#include "jsapi.h"
#include "nsJSUtils.h"

#include "nsFrameManager.h"
#include "nsDisplayList.h"
#include "ImageLayers.h"
#include "BasicLayers.h"
#include "imgIEncoder.h"

#include "nsIWritablePropertyBag2.h"

#define DEFAULT_CANVAS_WIDTH 300
#define DEFAULT_CANVAS_HEIGHT 150

using namespace mozilla;
using namespace mozilla::dom;
using namespace mozilla::layers;

nsGenericHTMLElement*
NS_NewHTMLCanvasElement(already_AddRefed<nsINodeInfo> aNodeInfo,
                        FromParser aFromParser)
{
  return new nsHTMLCanvasElement(aNodeInfo);
}

nsHTMLCanvasElement::nsHTMLCanvasElement(already_AddRefed<nsINodeInfo> aNodeInfo)
  : nsGenericHTMLElement(aNodeInfo), mWriteOnly(PR_FALSE)
{
}

nsHTMLCanvasElement::~nsHTMLCanvasElement()
{
}

NS_IMPL_CYCLE_COLLECTION_CLASS(nsHTMLCanvasElement)
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsHTMLCanvasElement,
                                                  nsGenericHTMLElement)
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mCurrentContext)
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END

NS_IMPL_ADDREF_INHERITED(nsHTMLCanvasElement, nsGenericElement)
NS_IMPL_RELEASE_INHERITED(nsHTMLCanvasElement, nsGenericElement)

DOMCI_NODE_DATA(HTMLCanvasElement, nsHTMLCanvasElement)

NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(nsHTMLCanvasElement)
  NS_HTML_CONTENT_INTERFACE_TABLE2(nsHTMLCanvasElement,
                                   nsIDOMHTMLCanvasElement,
                                   nsICanvasElementExternal)
  NS_HTML_CONTENT_INTERFACE_TABLE_TO_MAP_SEGUE(nsHTMLCanvasElement,
                                               nsGenericHTMLElement)
NS_HTML_CONTENT_INTERFACE_TABLE_TAIL_CLASSINFO(HTMLCanvasElement)

NS_IMPL_ELEMENT_CLONE(nsHTMLCanvasElement)

nsIntSize
nsHTMLCanvasElement::GetWidthHeight()
{
  nsIntSize size(0,0);
  const nsAttrValue* value;

  if ((value = GetParsedAttr(nsGkAtoms::width)) &&
      value->Type() == nsAttrValue::eInteger)
  {
      size.width = value->GetIntegerValue();
  }

  if ((value = GetParsedAttr(nsGkAtoms::height)) &&
      value->Type() == nsAttrValue::eInteger)
  {
      size.height = value->GetIntegerValue();
  }

  if (size.width <= 0)
    size.width = DEFAULT_CANVAS_WIDTH;
  if (size.height <= 0)
    size.height = DEFAULT_CANVAS_HEIGHT;

  return size;
}

NS_IMPL_UINT_ATTR_DEFAULT_VALUE(nsHTMLCanvasElement, Width, width, DEFAULT_CANVAS_WIDTH)
NS_IMPL_UINT_ATTR_DEFAULT_VALUE(nsHTMLCanvasElement, Height, height, DEFAULT_CANVAS_HEIGHT)
NS_IMPL_BOOL_ATTR(nsHTMLCanvasElement, MozOpaque, moz_opaque)

nsresult
nsHTMLCanvasElement::SetAttr(PRInt32 aNameSpaceID, nsIAtom* aName,
                             nsIAtom* aPrefix, const nsAString& aValue,
                             PRBool aNotify)
{
  nsresult rv = nsGenericHTMLElement::SetAttr(aNameSpaceID, aName, aPrefix, aValue,
                                              aNotify);
  if (NS_SUCCEEDED(rv) && mCurrentContext &&
      (aName == nsGkAtoms::width || aName == nsGkAtoms::height || aName == nsGkAtoms::moz_opaque))
  {
    rv = UpdateContext();
    NS_ENSURE_SUCCESS(rv, rv);
  }

  return rv;
}

nsresult
nsHTMLCanvasElement::CopyInnerTo(nsGenericElement* aDest) const
{
  nsresult rv = nsGenericHTMLElement::CopyInnerTo(aDest);
  NS_ENSURE_SUCCESS(rv, rv);
  if (aDest->GetOwnerDoc()->IsStaticDocument()) {
    nsHTMLCanvasElement* dest = static_cast<nsHTMLCanvasElement*>(aDest);
    nsCOMPtr<nsISupports> cxt;
    dest->GetContext(NS_LITERAL_STRING("2d"), JSVAL_VOID, getter_AddRefs(cxt));
    nsCOMPtr<nsIDOMCanvasRenderingContext2D> context2d = do_QueryInterface(cxt);
    if (context2d) {
      context2d->DrawImage(const_cast<nsHTMLCanvasElement*>(this),
                           0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0);
    }
  }
  return rv;
}

nsChangeHint
nsHTMLCanvasElement::GetAttributeChangeHint(const nsIAtom* aAttribute,
                                            PRInt32 aModType) const
{
  nsChangeHint retval =
    nsGenericHTMLElement::GetAttributeChangeHint(aAttribute, aModType);
  if (aAttribute == nsGkAtoms::width ||
      aAttribute == nsGkAtoms::height)
  {
    NS_UpdateHint(retval, NS_STYLE_HINT_REFLOW);
  } else if (aAttribute == nsGkAtoms::moz_opaque)
  {
    NS_UpdateHint(retval, NS_STYLE_HINT_VISUAL);
  }
  return retval;
}

PRBool
nsHTMLCanvasElement::ParseAttribute(PRInt32 aNamespaceID,
                                    nsIAtom* aAttribute,
                                    const nsAString& aValue,
                                    nsAttrValue& aResult)
{
  if (aNamespaceID == kNameSpaceID_None &&
      (aAttribute == nsGkAtoms::width || aAttribute == nsGkAtoms::height)) {
    return aResult.ParseNonNegativeIntValue(aValue);
  }

  return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                              aResult);
}


// nsHTMLCanvasElement::toDataURL

NS_IMETHODIMP
nsHTMLCanvasElement::ToDataURL(const nsAString& aType, const nsAString& aParams,
                               PRUint8 optional_argc, nsAString& aDataURL)
{
  // do a trust check if this is a write-only canvas
  // or if we're trying to use the 2-arg form
  if ((mWriteOnly || optional_argc >= 2) &&
      !nsContentUtils::IsCallerTrustedForRead()) {
    return NS_ERROR_DOM_SECURITY_ERR;
  }

  return ToDataURLImpl(aType, aParams, aDataURL);
}


// nsHTMLCanvasElement::toDataURLAs
//
// Native-callers only

NS_IMETHODIMP
nsHTMLCanvasElement::ToDataURLAs(const nsAString& aMimeType,
                                 const nsAString& aEncoderOptions,
                                 nsAString& aDataURL)
{
  return ToDataURLImpl(aMimeType, aEncoderOptions, aDataURL);
}

nsresult
nsHTMLCanvasElement::ExtractData(const nsAString& aType,
                                 const nsAString& aOptions,
                                 char*& aResult,
                                 PRUint32& aSize,
                                 bool& aFellBackToPNG)
{
  // note that if we don't have a current context, the spec says we're
  // supposed to just return transparent black pixels of the canvas
  // dimensions.
  nsRefPtr<gfxImageSurface> emptyCanvas;
  nsIntSize size = GetWidthHeight();
  if (!mCurrentContext) {
    emptyCanvas = new gfxImageSurface(gfxIntSize(size.width, size.height), gfxASurface::ImageFormatARGB32);
  }

  nsresult rv;

  // get image bytes
  nsCOMPtr<nsIInputStream> imgStream;
  nsCAutoString encoderType;
  encoderType.Assign(NS_ConvertUTF16toUTF8(aType));

 try_again:
  if (mCurrentContext) {
    rv = mCurrentContext->GetInputStream(nsPromiseFlatCString(encoderType).get(),
                                         nsPromiseFlatString(aOptions).get(),
                                         getter_AddRefs(imgStream));
  } else {
    // no context, so we have to encode the empty image we created above
    nsCString enccid("@mozilla.org/image/encoder;2?type=");
    enccid += encoderType;

    nsCOMPtr<imgIEncoder> encoder = do_CreateInstance(nsPromiseFlatCString(enccid).get(), &rv);
    if (NS_SUCCEEDED(rv) && encoder) {
      rv = encoder->InitFromData(emptyCanvas->Data(),
                                 size.width * size.height * 4,
                                 size.width,
                                 size.height,
                                 size.width * 4,
                                 imgIEncoder::INPUT_FORMAT_HOSTARGB,
                                 aOptions);
      if (NS_SUCCEEDED(rv)) {
        imgStream = do_QueryInterface(encoder);
      }
    } else {
      rv = NS_ERROR_FAILURE;
    }
  }

  if (NS_FAILED(rv) && !aFellBackToPNG) {
    // Try image/png instead.
    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
    aFellBackToPNG = true;
    encoderType.AssignLiteral("image/png");
    goto try_again;
  }

  // at this point, we either need to succeed or bail.
  NS_ENSURE_SUCCESS(rv, rv);

  // Generally, there will be only one chunk of data, and it will be available
  // for us to read right away, so optimize this case.
  PRUint32 bufSize;
  rv = imgStream->Available(&bufSize);
  CheckedUint32 safeBufSize(bufSize);
  NS_ENSURE_SUCCESS(rv, rv);

  // ...leave a little extra room so we can call read again and make sure we
  // got everything. 16 bytes for better padding (maybe)
  safeBufSize += 16;
  NS_ENSURE_TRUE(safeBufSize.valid(), NS_ERROR_FAILURE);
  aSize = 0;
  aResult = (char*)PR_Malloc(safeBufSize.value());
  if (!aResult)
    return NS_ERROR_OUT_OF_MEMORY;
  PRUint32 numReadThisTime = 0;
  while ((rv = imgStream->Read(&aResult[aSize], safeBufSize.value() - aSize,
                               &numReadThisTime)) == NS_OK &&
         numReadThisTime > 0) {
    aSize += numReadThisTime;
    if (aSize == safeBufSize.value()) {
      // need a bigger buffer, just double
      safeBufSize *= 2;
      if (!safeBufSize.valid()) {
        PR_Free(aResult);
        return NS_ERROR_FAILURE;
      }
      char* newImgData = (char*)PR_Realloc(aResult, safeBufSize.value());
      if (! newImgData) {
        PR_Free(aResult);
        return NS_ERROR_OUT_OF_MEMORY;
      }
      aResult = newImgData;
    }
  }

  return NS_OK;
}

nsresult
nsHTMLCanvasElement::ToDataURLImpl(const nsAString& aMimeType,
                                   const nsAString& aEncoderOptions,
                                   nsAString& aDataURL)
{
  bool fallbackToPNG = false;

  PRUint32 imgSize = 0;
  char* imgData;

  nsresult rv = ExtractData(aMimeType, aEncoderOptions, imgData,
                            imgSize, fallbackToPNG);
  NS_ENSURE_SUCCESS(rv, rv);

  // base 64, result will be NULL terminated
  char* encodedImg = PL_Base64Encode(imgData, imgSize, nsnull);
  PR_Free(imgData);
  if (!encodedImg) // not sure why this would fail
    return NS_ERROR_OUT_OF_MEMORY;

  // build data URL string
  if (fallbackToPNG)
    aDataURL = NS_LITERAL_STRING("data:image/png;base64,") +
      NS_ConvertUTF8toUTF16(encodedImg);
  else
    aDataURL = NS_LITERAL_STRING("data:") + aMimeType +
      NS_LITERAL_STRING(";base64,") + NS_ConvertUTF8toUTF16(encodedImg);

  PR_Free(encodedImg);

  return NS_OK;
}

NS_IMETHODIMP
nsHTMLCanvasElement::MozGetAsFile(const nsAString& aName,
                                  const nsAString& aType,
                                  PRUint8 optional_argc,
                                  nsIDOMFile** aResult)
{
  // do a trust check if this is a write-only canvas
  if ((mWriteOnly) &&
      !nsContentUtils::IsCallerTrustedForRead()) {
    return NS_ERROR_DOM_SECURITY_ERR;
  }

  return MozGetAsFileImpl(aName, aType, aResult);
}

nsresult
nsHTMLCanvasElement::MozGetAsFileImpl(const nsAString& aName,
                                      const nsAString& aType,
                                      nsIDOMFile** aResult)
{
  bool fallbackToPNG = false;
  PRUint32 imgSize = 0;
  char* imgData;

  nsresult rv = ExtractData(aType, EmptyString(), imgData,
                            imgSize, fallbackToPNG);
  NS_ENSURE_SUCCESS(rv, rv);

  nsAutoString type(aType);
  if (fallbackToPNG) {
    type.AssignLiteral("image/png");
  }

  // The DOMFile takes ownership of the buffer
  nsRefPtr<nsDOMMemoryFile> file =
    new nsDOMMemoryFile((void*)imgData, imgSize, aName, type);

  return CallQueryInterface(file, aResult);
}

nsresult
nsHTMLCanvasElement::GetContextHelper(const nsAString& aContextId,
                                      nsICanvasRenderingContextInternal **aContext)
{
  NS_ENSURE_ARG(aContext);

  NS_LossyConvertUTF16toASCII ctxId(aContextId);

  // check that ctxId is clamped to A-Za-z0-9_-
  for (PRUint32 i = 0; i < ctxId.Length(); i++) {
    if ((ctxId[i] < 'A' || ctxId[i] > 'Z') &&
        (ctxId[i] < 'a' || ctxId[i] > 'z') &&
        (ctxId[i] < '0' || ctxId[i] > '9') &&
        (ctxId[i] != '-') &&
        (ctxId[i] != '_'))
    {
      // XXX ERRMSG we need to report an error to developers here! (bug 329026)
      return NS_OK;
    }
  }

  nsCString ctxString("@mozilla.org/content/canvas-rendering-context;1?id=");
  ctxString.Append(ctxId);

  nsresult rv;
  nsCOMPtr<nsICanvasRenderingContextInternal> ctx =
    do_CreateInstance(nsPromiseFlatCString(ctxString).get(), &rv);
  if (rv == NS_ERROR_OUT_OF_MEMORY) {
    *aContext = nsnull;
    return NS_ERROR_OUT_OF_MEMORY;
  }
  if (NS_FAILED(rv)) {
    *aContext = nsnull;
    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
    return NS_OK;
  }

  rv = ctx->SetCanvasElement(this);
  if (NS_FAILED(rv)) {
    *aContext = nsnull;
    return rv;
  }

  *aContext = ctx.forget().get();

  return rv;
}

NS_IMETHODIMP
nsHTMLCanvasElement::GetContext(const nsAString& aContextId,
                                const jsval& aContextOptions,
                                nsISupports **aContext)
{
  nsresult rv;

  if (mCurrentContextId.IsEmpty()) {
    rv = GetContextHelper(aContextId, getter_AddRefs(mCurrentContext));
    NS_ENSURE_SUCCESS(rv, rv);
    if (!mCurrentContext) {
      return NS_OK;
    }

    // Ensure that the context participates in CC.  Note that returning a
    // CC participant from QI doesn't addref.
    nsXPCOMCycleCollectionParticipant *cp = nsnull;
    CallQueryInterface(mCurrentContext, &cp);
    if (!cp) {
      mCurrentContext = nsnull;
      return NS_ERROR_FAILURE;
    }

    rv = mCurrentContext->SetCanvasElement(this);
    if (NS_FAILED(rv)) {
      mCurrentContext = nsnull;
      return rv;
    }

    nsCOMPtr<nsIPropertyBag> contextProps;
    if (!JSVAL_IS_NULL(aContextOptions) &&
        !JSVAL_IS_VOID(aContextOptions))
    {
      JSContext *cx = nsContentUtils::GetCurrentJSContext();

      nsCOMPtr<nsIWritablePropertyBag2> newProps;

      // note: if any contexts end up supporting something other
      // than objects, e.g. plain strings, then we'll need to expand
      // this to know how to create nsISupportsStrings etc.
      if (JSVAL_IS_OBJECT(aContextOptions)) {
        newProps = do_CreateInstance("@mozilla.org/hash-property-bag;1");

        JSObject *opts = JSVAL_TO_OBJECT(aContextOptions);
        JSIdArray *props = JS_Enumerate(cx, opts);
        for (int i = 0; props && i < props->length; ++i) {
          jsid propid = props->vector[i];
          jsval propname, propval;
          if (!JS_IdToValue(cx, propid, &propname) ||
              !JS_GetPropertyById(cx, opts, propid, &propval))
          {
            continue;
          }

          JSString *propnameString = JS_ValueToString(cx, propname);
          nsDependentJSString pstr;
          if (!propnameString || !pstr.init(cx, propnameString)) {
            mCurrentContext = nsnull;
            return NS_ERROR_FAILURE;
          }

          if (JSVAL_IS_BOOLEAN(propval)) {
            newProps->SetPropertyAsBool(pstr, propval == JSVAL_TRUE ? PR_TRUE : PR_FALSE);
          } else if (JSVAL_IS_INT(propval)) {
            newProps->SetPropertyAsInt32(pstr, JSVAL_TO_INT(propval));
          } else if (JSVAL_IS_DOUBLE(propval)) {
            newProps->SetPropertyAsDouble(pstr, JSVAL_TO_DOUBLE(propval));
          } else if (JSVAL_IS_STRING(propval)) {
            JSString *propvalString = JS_ValueToString(cx, propval);
            nsDependentJSString vstr;
            if (!propvalString || !vstr.init(cx, propvalString)) {
              mCurrentContext = nsnull;
              return NS_ERROR_FAILURE;
            }

            newProps->SetPropertyAsAString(pstr, vstr);
          }
        }
      }

      contextProps = newProps;
    }

    rv = UpdateContext(contextProps);
    if (NS_FAILED(rv)) {
      mCurrentContext = nsnull;
      return rv;
    }

    mCurrentContextId.Assign(aContextId);
  } else if (!mCurrentContextId.Equals(aContextId)) {
    //XXX eventually allow for more than one active context on a given canvas
    return NS_OK;
  }

  NS_ADDREF (*aContext = mCurrentContext);
  return NS_OK;
}

NS_IMETHODIMP
nsHTMLCanvasElement::MozGetIPCContext(const nsAString& aContextId,
                                      nsISupports **aContext)
{
#ifdef MOZ_IPC
  if(!nsContentUtils::IsCallerTrustedForRead()) {
    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
    return NS_ERROR_DOM_SECURITY_ERR;
  }

  // We only support 2d shmem contexts for now.
  if (!aContextId.Equals(NS_LITERAL_STRING("2d")))
    return NS_ERROR_INVALID_ARG;

  nsresult rv;

  if (mCurrentContextId.IsEmpty()) {
    rv = GetContextHelper(aContextId, getter_AddRefs(mCurrentContext));
    NS_ENSURE_SUCCESS(rv, rv);
    if (!mCurrentContext) {
      return NS_OK;
    }

    mCurrentContext->SetIsIPC(PR_TRUE);

    rv = UpdateContext();
    if (NS_FAILED(rv)) {
      mCurrentContext = nsnull;
      return rv;
    }

    mCurrentContextId.Assign(aContextId);
  } else if (!mCurrentContextId.Equals(aContextId)) {
    //XXX eventually allow for more than one active context on a given canvas
    return NS_ERROR_INVALID_ARG;
  }

  NS_ADDREF (*aContext = mCurrentContext);
  return NS_OK;
#else
  return NS_ERROR_NOT_IMPLEMENTED;
#endif
}

nsresult
nsHTMLCanvasElement::UpdateContext(nsIPropertyBag *aNewContextOptions)
{
  if (!mCurrentContext)
    return NS_OK;

  nsresult rv = NS_OK;

  rv = mCurrentContext->SetIsOpaque(GetIsOpaque());
  if (NS_FAILED(rv))
    return rv;

  rv = mCurrentContext->SetContextOptions(aNewContextOptions);
  if (NS_FAILED(rv))
    return rv;

  nsIntSize sz = GetWidthHeight();
  rv = mCurrentContext->SetDimensions(sz.width, sz.height);
  if (NS_FAILED(rv))
    return rv;

  return rv;
}

nsIFrame *
nsHTMLCanvasElement::GetPrimaryCanvasFrame()
{
  return GetPrimaryFrame(Flush_Frames);
}

nsIntSize
nsHTMLCanvasElement::GetSize()
{
  return GetWidthHeight();
}

PRBool
nsHTMLCanvasElement::IsWriteOnly()
{
  return mWriteOnly;
}

void
nsHTMLCanvasElement::SetWriteOnly()
{
  mWriteOnly = PR_TRUE;
}

void
nsHTMLCanvasElement::InvalidateFrame(const gfxRect* damageRect)
{
  // We don't need to flush anything here; if there's no frame or if
  // we plan to reframe we don't need to invalidate it anyway.
  nsIFrame *frame = GetPrimaryFrame();
  if (!frame)
    return;

  frame->MarkLayersActive();

  nsRect invalRect;
  nsRect contentArea = frame->GetContentRect();
  if (damageRect) {
    nsIntSize size = GetWidthHeight();

    // damageRect and size are in CSS pixels; contentArea is in appunits
    // We want a rect in appunits; so avoid doing pixels-to-appunits and
    // vice versa conversion here.
    gfxRect realRect(*damageRect);
    realRect.Scale(contentArea.width / gfxFloat(size.width),
                   contentArea.height / gfxFloat(size.height));
    realRect.RoundOut();

    // then make it a nsRect
    invalRect = nsRect(realRect.X(), realRect.Y(),
                       realRect.Width(), realRect.Height());
  } else {
    invalRect = nsRect(nsPoint(0, 0), contentArea.Size());
  }
  invalRect.MoveBy(contentArea.TopLeft() - frame->GetPosition());

  Layer* layer = frame->InvalidateLayer(invalRect, nsDisplayItem::TYPE_CANVAS);
  if (layer) {
    static_cast<CanvasLayer*>(layer)->Updated();
  }
}

PRInt32
nsHTMLCanvasElement::CountContexts()
{
  if (mCurrentContext)
    return 1;

  return 0;
}

nsICanvasRenderingContextInternal *
nsHTMLCanvasElement::GetContextAtIndex (PRInt32 index)
{
  if (mCurrentContext && index == 0)
    return mCurrentContext.get();

  return NULL;
}

PRBool
nsHTMLCanvasElement::GetIsOpaque()
{
  return HasAttr(kNameSpaceID_None, nsGkAtoms::moz_opaque);
}

already_AddRefed<CanvasLayer>
nsHTMLCanvasElement::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                    CanvasLayer *aOldLayer,
                                    LayerManager *aManager)
{
  if (!mCurrentContext)
    return nsnull;

  return mCurrentContext->GetCanvasLayer(aBuilder, aOldLayer, aManager);
}

void
nsHTMLCanvasElement::MarkContextClean()
{
  if (!mCurrentContext)
    return;

  mCurrentContext->MarkContextClean();
}

NS_IMETHODIMP_(nsIntSize)
nsHTMLCanvasElement::GetSizeExternal()
{
  return GetWidthHeight();
}

NS_IMETHODIMP
nsHTMLCanvasElement::RenderContextsExternal(gfxContext *aContext, gfxPattern::GraphicsFilter aFilter)
{
  if (!mCurrentContext)
    return NS_OK;

  return mCurrentContext->Render(aContext, aFilter);
}