widget/nsBaseDragService.cpp
author Chris H-C <chutten@mozilla.com>
Mon, 04 Jul 2016 11:16:05 -0400
changeset 312997 df28918fe2361f0b54ca9ce4773a29c4c0675d06
parent 310949 564549c354b038a465c0b3fc245da3cab8753eab
child 318173 bd7461a1ed09447f4d38b4911f0e83933f9d875b
permissions -rw-r--r--
bug 1218576 - Support remote accumulation via JS histograms. r=gfritzsche The JS histograms, too, need to dispatch their accumulations from child to parent. JSHistograms_Add now only supports histograms that are in gHistogramsMap or that were created in the parent process. After bug 1288745, maybe we'll be able to change this to be less convoluted. MozReview-Commit-ID: 3qTH89YKbGP

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsBaseDragService.h"
#include "nsITransferable.h"

#include "nsIServiceManager.h"
#include "nsITransferable.h"
#include "nsISupportsArray.h"
#include "nsSize.h"
#include "nsXPCOM.h"
#include "nsISupportsPrimitives.h"
#include "nsCOMPtr.h"
#include "nsIInterfaceRequestorUtils.h"
#include "nsIFrame.h"
#include "nsIDocument.h"
#include "nsIContent.h"
#include "nsIPresShell.h"
#include "nsViewManager.h"
#include "nsIDOMNode.h"
#include "nsIDOMDragEvent.h"
#include "nsISelection.h"
#include "nsISelectionPrivate.h"
#include "nsPresContext.h"
#include "nsIDOMDataTransfer.h"
#include "nsIImageLoadingContent.h"
#include "imgIContainer.h"
#include "imgIRequest.h"
#include "ImageRegion.h"
#include "nsRegion.h"
#include "nsXULPopupManager.h"
#include "nsMenuPopupFrame.h"
#include "SVGImageContext.h"
#include "mozilla/MouseEvents.h"
#include "mozilla/Preferences.h"
#include "mozilla/gfx/2D.h"
#include "mozilla/Unused.h"
#include "nsFrameLoader.h"
#include "TabParent.h"

#include "gfxContext.h"
#include "gfxPlatform.h"
#include <algorithm>

using namespace mozilla;
using namespace mozilla::dom;
using namespace mozilla::gfx;
using namespace mozilla::image;

#define DRAGIMAGES_PREF "nglayout.enable_drag_images"

nsBaseDragService::nsBaseDragService()
  : mCanDrop(false), mOnlyChromeDrop(false), mDoingDrag(false),
    mHasImage(false), mUserCancelled(false),
    mDragEventDispatchedToChildProcess(false),
    mDragAction(DRAGDROP_ACTION_NONE),
    mDragActionFromChildProcess(DRAGDROP_ACTION_UNINITIALIZED), mTargetSize(0,0),
    mContentPolicyType(nsIContentPolicy::TYPE_OTHER),
    mScreenX(-1), mScreenY(-1), mSuppressLevel(0),
    mInputSource(nsIDOMMouseEvent::MOZ_SOURCE_MOUSE)
{
}

nsBaseDragService::~nsBaseDragService()
{
}

NS_IMPL_ISUPPORTS(nsBaseDragService, nsIDragService, nsIDragSession)

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::SetCanDrop(bool aCanDrop)
{
  mCanDrop = aCanDrop;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::GetCanDrop(bool * aCanDrop)
{
  *aCanDrop = mCanDrop;
  return NS_OK;
}
//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::SetOnlyChromeDrop(bool aOnlyChrome)
{
  mOnlyChromeDrop = aOnlyChrome;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::GetOnlyChromeDrop(bool* aOnlyChrome)
{
  *aOnlyChrome = mOnlyChromeDrop;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::SetDragAction(uint32_t anAction)
{
  mDragAction = anAction;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::GetDragAction(uint32_t * anAction)
{
  *anAction = mDragAction;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::SetTargetSize(nsSize aDragTargetSize)
{
  mTargetSize = aDragTargetSize;
  return NS_OK;
}

//---------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::GetTargetSize(nsSize * aDragTargetSize)
{
  *aDragTargetSize = mTargetSize;
  return NS_OK;
}

//-------------------------------------------------------------------------

NS_IMETHODIMP
nsBaseDragService::GetNumDropItems(uint32_t * aNumItems)
{
  *aNumItems = 0;
  return NS_ERROR_FAILURE;
}


//
// GetSourceDocument
//
// Returns the DOM document where the drag was initiated. This will be
// nullptr if the drag began outside of our application.
//
NS_IMETHODIMP
nsBaseDragService::GetSourceDocument(nsIDOMDocument** aSourceDocument)
{
  *aSourceDocument = mSourceDocument.get();
  NS_IF_ADDREF(*aSourceDocument);

  return NS_OK;
}

//
// GetSourceNode
//
// Returns the DOM node where the drag was initiated. This will be
// nullptr if the drag began outside of our application.
//
NS_IMETHODIMP
nsBaseDragService::GetSourceNode(nsIDOMNode** aSourceNode)
{
  *aSourceNode = mSourceNode.get();
  NS_IF_ADDREF(*aSourceNode);

  return NS_OK;
}


//-------------------------------------------------------------------------

NS_IMETHODIMP
nsBaseDragService::GetData(nsITransferable * aTransferable,
                           uint32_t aItemIndex)
{
  return NS_ERROR_FAILURE;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::IsDataFlavorSupported(const char *aDataFlavor,
                                         bool *_retval)
{
  return NS_ERROR_FAILURE;
}

NS_IMETHODIMP
nsBaseDragService::GetDataTransfer(nsIDOMDataTransfer** aDataTransfer)
{
  *aDataTransfer = mDataTransfer;
  NS_IF_ADDREF(*aDataTransfer);
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::SetDataTransfer(nsIDOMDataTransfer* aDataTransfer)
{
  mDataTransfer = aDataTransfer;
  return NS_OK;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::InvokeDragSession(nsIDOMNode *aDOMNode,
                                     nsISupportsArray* aTransferableArray,
                                     nsIScriptableRegion* aDragRgn,
                                     uint32_t aActionType,
                                     nsContentPolicyType aContentPolicyType =
                                       nsIContentPolicy::TYPE_OTHER)
{
  PROFILER_LABEL_FUNC(js::ProfileEntry::Category::OTHER);

  NS_ENSURE_TRUE(aDOMNode, NS_ERROR_INVALID_ARG);
  NS_ENSURE_TRUE(mSuppressLevel == 0, NS_ERROR_FAILURE);

  // stash the document of the dom node
  aDOMNode->GetOwnerDocument(getter_AddRefs(mSourceDocument));
  mSourceNode = aDOMNode;
  mContentPolicyType = aContentPolicyType;
  mEndDragPoint = LayoutDeviceIntPoint(0, 0);

  // When the mouse goes down, the selection code starts a mouse
  // capture. However, this gets in the way of determining drag
  // feedback for things like trees because the event coordinates
  // are in the wrong coord system, so turn off mouse capture.
  nsIPresShell::ClearMouseCapture(nullptr);

  nsresult rv = InvokeDragSessionImpl(aTransferableArray,
                                      aDragRgn, aActionType);

  if (NS_FAILED(rv)) {
    mSourceNode = nullptr;
    mSourceDocument = nullptr;
  }

  return rv;
}

NS_IMETHODIMP
nsBaseDragService::InvokeDragSessionWithImage(nsIDOMNode* aDOMNode,
                                              nsISupportsArray* aTransferableArray,
                                              nsIScriptableRegion* aRegion,
                                              uint32_t aActionType,
                                              nsIDOMNode* aImage,
                                              int32_t aImageX, int32_t aImageY,
                                              nsIDOMDragEvent* aDragEvent,
                                              nsIDOMDataTransfer* aDataTransfer)
{
  NS_ENSURE_TRUE(aDragEvent, NS_ERROR_NULL_POINTER);
  NS_ENSURE_TRUE(aDataTransfer, NS_ERROR_NULL_POINTER);
  NS_ENSURE_TRUE(mSuppressLevel == 0, NS_ERROR_FAILURE);

  mDataTransfer = aDataTransfer;
  mSelection = nullptr;
  mHasImage = true;
  mDragPopup = nullptr;
  mImage = aImage;
  mImageOffset = CSSIntPoint(aImageX, aImageY);

  aDragEvent->GetScreenX(&mScreenX);
  aDragEvent->GetScreenY(&mScreenY);
  aDragEvent->GetMozInputSource(&mInputSource);

  nsresult rv = InvokeDragSession(aDOMNode, aTransferableArray,
                                  aRegion, aActionType,
                                  nsIContentPolicy::TYPE_INTERNAL_IMAGE);

  if (NS_FAILED(rv)) {
    mImage = nullptr;
    mHasImage = false;
    mDataTransfer = nullptr;
  }

  return rv;
}

NS_IMETHODIMP
nsBaseDragService::InvokeDragSessionWithSelection(nsISelection* aSelection,
                                                  nsISupportsArray* aTransferableArray,
                                                  uint32_t aActionType,
                                                  nsIDOMDragEvent* aDragEvent,
                                                  nsIDOMDataTransfer* aDataTransfer)
{
  NS_ENSURE_TRUE(aSelection, NS_ERROR_NULL_POINTER);
  NS_ENSURE_TRUE(aDragEvent, NS_ERROR_NULL_POINTER);
  NS_ENSURE_TRUE(mSuppressLevel == 0, NS_ERROR_FAILURE);

  mDataTransfer = aDataTransfer;
  mSelection = aSelection;
  mHasImage = true;
  mDragPopup = nullptr;
  mImage = nullptr;
  mImageOffset = CSSIntPoint();

  aDragEvent->GetScreenX(&mScreenX);
  aDragEvent->GetScreenY(&mScreenY);
  aDragEvent->GetMozInputSource(&mInputSource);

  // just get the focused node from the selection
  // XXXndeakin this should actually be the deepest node that contains both
  // endpoints of the selection
  nsCOMPtr<nsIDOMNode> node;
  aSelection->GetFocusNode(getter_AddRefs(node));

  nsresult rv = InvokeDragSession(node, aTransferableArray,
                                  nullptr, aActionType,
                                  nsIContentPolicy::TYPE_OTHER);

  if (NS_FAILED(rv)) {
    mHasImage = false;
    mSelection = nullptr;
    mDataTransfer = nullptr;
  }

  return rv;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::GetCurrentSession(nsIDragSession ** aSession)
{
  if (!aSession)
    return NS_ERROR_INVALID_ARG;

  // "this" also implements a drag session, so say we are one but only
  // if there is currently a drag going on.
  if (!mSuppressLevel && mDoingDrag) {
    *aSession = this;
    NS_ADDREF(*aSession);      // addRef because we're a "getter"
  }
  else
    *aSession = nullptr;

  return NS_OK;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::StartDragSession()
{
  if (mDoingDrag) {
    return NS_ERROR_FAILURE;
  }
  mDoingDrag = true;
  // By default dispatch drop also to content.
  mOnlyChromeDrop = false;

  return NS_OK;
}

void
nsBaseDragService::OpenDragPopup()
{
  if (mDragPopup) {
    nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
    if (pm) {
      pm->ShowPopupAtScreen(mDragPopup, mScreenX - mImageOffset.x,
                            mScreenY - mImageOffset.y, false, nullptr);
    }
  }
}

int32_t
nsBaseDragService::TakeChildProcessDragAction()
{
  // If the last event was dispatched to the child process, use the drag action
  // assigned from it instead and return it. DRAGDROP_ACTION_UNINITIALIZED is
  // returned otherwise.
  int32_t retval = DRAGDROP_ACTION_UNINITIALIZED;
  if (TakeDragEventDispatchedToChildProcess() &&
      mDragActionFromChildProcess != DRAGDROP_ACTION_UNINITIALIZED) {
    retval = mDragActionFromChildProcess;
  }

  return retval;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::EndDragSession(bool aDoneDrag)
{
  if (!mDoingDrag) {
    return NS_ERROR_FAILURE;
  }

  if (aDoneDrag && !mSuppressLevel) {
    FireDragEventAtSource(eDragEnd);
  }

  if (mDragPopup) {
    nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
    if (pm) {
      pm->HidePopup(mDragPopup, false, true, false, false);
    }
  }

  for (uint32_t i = 0; i < mChildProcesses.Length(); ++i) {
    mozilla::Unused << mChildProcesses[i]->SendEndDragSession(aDoneDrag,
                                                              mUserCancelled,
                                                              mEndDragPoint);
  }
  mChildProcesses.Clear();

  mDoingDrag = false;
  mCanDrop = false;

  // release the source we've been holding on to.
  mSourceDocument = nullptr;
  mSourceNode = nullptr;
  mSelection = nullptr;
  mDataTransfer = nullptr;
  mHasImage = false;
  mUserCancelled = false;
  mDragPopup = nullptr;
  mImage = nullptr;
  mImageOffset = CSSIntPoint();
  mScreenX = -1;
  mScreenY = -1;
  mEndDragPoint = LayoutDeviceIntPoint(0, 0);
  mInputSource = nsIDOMMouseEvent::MOZ_SOURCE_MOUSE;

  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::FireDragEventAtSource(EventMessage aEventMessage)
{
  if (mSourceNode && !mSuppressLevel) {
    nsCOMPtr<nsIDocument> doc = do_QueryInterface(mSourceDocument);
    if (doc) {
      nsCOMPtr<nsIPresShell> presShell = doc->GetShell();
      if (presShell) {
        nsEventStatus status = nsEventStatus_eIgnore;
        WidgetDragEvent event(true, aEventMessage, nullptr);
        event.inputSource = mInputSource;
        if (aEventMessage == eDragEnd) {
          event.mRefPoint = mEndDragPoint;
          event.mUserCancelled = mUserCancelled;
        }

        // Send the drag event to APZ, which needs to know about them to be
        // able to accurately detect the end of a drag gesture.
        if (nsPresContext* presContext = presShell->GetPresContext()) {
          if (nsCOMPtr<nsIWidget> widget = presContext->GetRootWidget()) {
            widget->DispatchEventToAPZOnly(&event);
          }
        }

        nsCOMPtr<nsIContent> content = do_QueryInterface(mSourceNode);
        return presShell->HandleDOMEventWithTarget(content, &event, &status);
      }
    }
  }

  return NS_OK;
}

/* This is used by Windows and Mac to update the position of a popup being
 * used as a drag image during the drag. This isn't used on GTK as it manages
 * the drag popup itself.
 */
NS_IMETHODIMP
nsBaseDragService::DragMoved(int32_t aX, int32_t aY)
{
  if (mDragPopup) {
    nsIFrame* frame = mDragPopup->GetPrimaryFrame();
    if (frame && frame->GetType() == nsGkAtoms::menuPopupFrame) {
      CSSIntPoint cssPos = RoundedToInt(LayoutDeviceIntPoint(aX, aY) /
          frame->PresContext()->CSSToDevPixelScale()) - mImageOffset;
      (static_cast<nsMenuPopupFrame *>(frame))->MoveTo(cssPos, true);
    }
  }

  return NS_OK;
}

static nsIPresShell*
GetPresShellForContent(nsIDOMNode* aDOMNode)
{
  nsCOMPtr<nsIContent> content = do_QueryInterface(aDOMNode);
  if (!content)
    return nullptr;

  nsCOMPtr<nsIDocument> document = content->GetUncomposedDoc();
  if (document) {
    document->FlushPendingNotifications(Flush_Display);

    return document->GetShell();
  }

  return nullptr;
}

nsresult
nsBaseDragService::DrawDrag(nsIDOMNode* aDOMNode,
                            nsIScriptableRegion* aRegion,
                            int32_t aScreenX, int32_t aScreenY,
                            nsIntRect* aScreenDragRect,
                            RefPtr<SourceSurface>* aSurface,
                            nsPresContext** aPresContext)
{
  *aSurface = nullptr;
  *aPresContext = nullptr;

  // use a default size, in case of an error.
  aScreenDragRect->x = aScreenX - mImageOffset.x;
  aScreenDragRect->y = aScreenY - mImageOffset.y;
  aScreenDragRect->width = 1;
  aScreenDragRect->height = 1;

  // if a drag image was specified, use that, otherwise, use the source node
  nsCOMPtr<nsIDOMNode> dragNode = mImage ? mImage.get() : aDOMNode;

  // get the presshell for the node being dragged. If the drag image is not in
  // a document or has no frame, get the presshell from the source drag node
  nsIPresShell* presShell = GetPresShellForContent(dragNode);
  if (!presShell && mImage)
    presShell = GetPresShellForContent(aDOMNode);
  if (!presShell)
    return NS_ERROR_FAILURE;

  *aPresContext = presShell->GetPresContext();

  nsCOMPtr<nsIFrameLoaderOwner> flo = do_QueryInterface(dragNode);
  if (flo) {
    RefPtr<nsFrameLoader> fl = flo->GetFrameLoader();
    if (fl) {
      mozilla::dom::TabParent* tp =
        static_cast<mozilla::dom::TabParent*>(fl->GetRemoteBrowser());
      if (tp) {
        int32_t x, y;
        tp->TakeDragVisualization(*aSurface, x, y);
        if (*aSurface) {
          if (mImage) {
            // Just clear the surface if chrome has overridden it with an image.
            *aSurface = nullptr;
          } else {
            nsIFrame* f = fl->GetOwnerContent()->GetPrimaryFrame();
            if (f) {
              aScreenDragRect->x = x;
              aScreenDragRect->y = y;
              aScreenDragRect->width = (*aSurface)->GetSize().width;
              aScreenDragRect->height = (*aSurface)->GetSize().height;
            }
            return NS_OK;
          }
        }
      }
    }
  }

  // convert mouse position to dev pixels of the prescontext
  int32_t sx = aScreenX, sy = aScreenY;
  ConvertToUnscaledDevPixels(*aPresContext, &sx, &sy);

  aScreenDragRect->x = sx - mImageOffset.x;
  aScreenDragRect->y = sy - mImageOffset.y;

  // check if drag images are disabled
  bool enableDragImages = Preferences::GetBool(DRAGIMAGES_PREF, true);

  // didn't want an image, so just set the screen rectangle to the frame size
  if (!enableDragImages || !mHasImage) {
    // if a region was specified, set the screen rectangle to the area that
    // the region occupies
    if (aRegion) {
      // the region's coordinates are relative to the root frame
      nsIFrame* rootFrame = presShell->GetRootFrame();
      if (rootFrame) {
        nsIntRect dragRect;
        aRegion->GetBoundingBox(&dragRect.x, &dragRect.y, &dragRect.width, &dragRect.height);
        dragRect = ToAppUnits(dragRect, nsPresContext::AppUnitsPerCSSPixel()).
                            ToOutsidePixels((*aPresContext)->AppUnitsPerDevPixel());

        nsIntRect screenRect = rootFrame->GetScreenRect();
        aScreenDragRect->SetRect(screenRect.x + dragRect.x, screenRect.y + dragRect.y,
                                 dragRect.width, dragRect.height);
      }
    }
    else {
      // otherwise, there was no region so just set the rectangle to
      // the size of the primary frame of the content.
      nsCOMPtr<nsIContent> content = do_QueryInterface(dragNode);
      nsIFrame* frame = content->GetPrimaryFrame();
      if (frame) {
        nsIntRect screenRect = frame->GetScreenRect();
        aScreenDragRect->SetRect(screenRect.x, screenRect.y,
                                 screenRect.width, screenRect.height);
      }
    }

    return NS_OK;
  }

  // draw the image for selections
  if (mSelection) {
    nsIntPoint pnt(aScreenDragRect->x, aScreenDragRect->y);
    *aSurface = presShell->RenderSelection(mSelection, pnt, aScreenDragRect,
        mImage ? 0 : nsIPresShell::RENDER_AUTO_SCALE);
    return NS_OK;
  }

  // if a custom image was specified, check if it is an image node and draw
  // using the source rather than the displayed image. But if mImage isn't
  // an image or canvas, fall through to RenderNode below.
  if (mImage) {
    nsCOMPtr<nsIContent> content = do_QueryInterface(dragNode);
    HTMLCanvasElement *canvas = HTMLCanvasElement::FromContentOrNull(content);
    if (canvas) {
      return DrawDragForImage(nullptr, canvas, sx, sy,
                              aScreenDragRect, aSurface);
    }

    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(dragNode);
    // for image nodes, create the drag image from the actual image data
    if (imageLoader) {
      return DrawDragForImage(imageLoader, nullptr, sx, sy,
                              aScreenDragRect, aSurface);
    }

    // If the image is a popup, use that as the image. This allows custom drag
    // images that can change during the drag, but means that any platform
    // default image handling won't occur.
    // XXXndeakin this should be chrome-only

    nsIFrame* frame = content->GetPrimaryFrame();
    if (frame && frame->GetType() == nsGkAtoms::menuPopupFrame) {
      mDragPopup = content;
    }
  }

  if (!mDragPopup) {
    // otherwise, just draw the node
    nsIntRegion clipRegion;
    uint32_t renderFlags = mImage ? 0 : nsIPresShell::RENDER_AUTO_SCALE;
    if (aRegion) {
      aRegion->GetRegion(&clipRegion);
    }

    if (renderFlags) {
      nsCOMPtr<nsIDOMNode> child;
      nsCOMPtr<nsIDOMNodeList> childList;
      uint32_t length;
      uint32_t count = 0;
      nsAutoString childNodeName;

      if (NS_SUCCEEDED(dragNode->GetChildNodes(getter_AddRefs(childList))) &&
          NS_SUCCEEDED(childList->GetLength(&length))) {
        // check every childnode for being a img-tag
        while (count < length) {
          if (NS_FAILED(childList->Item(count, getter_AddRefs(child))) ||
              NS_FAILED(child->GetNodeName(childNodeName))) {
            break;
          }
          // here the node is checked for being a img-tag
          if (childNodeName.LowerCaseEqualsLiteral("img")) {
            // if the dragnnode contains a image, set RENDER_IS_IMAGE flag
            renderFlags = renderFlags | nsIPresShell::RENDER_IS_IMAGE;
            break;
          }
          count++;
        }
      }
    }
    nsIntPoint pnt(aScreenDragRect->x, aScreenDragRect->y);
    *aSurface = presShell->RenderNode(dragNode, aRegion ? &clipRegion : nullptr,
                                    pnt, aScreenDragRect,
                                    renderFlags);
  }

  // if an image was specified, reposition the drag rectangle to
  // the supplied offset in mImageX and mImageY.
  if (mImage) {
    aScreenDragRect->x = sx - mImageOffset.x;
    aScreenDragRect->y = sy - mImageOffset.y;
  }

  return NS_OK;
}

nsresult
nsBaseDragService::DrawDragForImage(nsIImageLoadingContent* aImageLoader,
                                    HTMLCanvasElement* aCanvas,
                                    int32_t aScreenX, int32_t aScreenY,
                                    nsIntRect* aScreenDragRect,
                                    RefPtr<SourceSurface>* aSurface)
{
  nsCOMPtr<imgIContainer> imgContainer;
  if (aImageLoader) {
    nsCOMPtr<imgIRequest> imgRequest;
    nsresult rv = aImageLoader->GetRequest(nsIImageLoadingContent::CURRENT_REQUEST,
                                          getter_AddRefs(imgRequest));
    NS_ENSURE_SUCCESS(rv, rv);
    if (!imgRequest)
      return NS_ERROR_NOT_AVAILABLE;

    rv = imgRequest->GetImage(getter_AddRefs(imgContainer));
    NS_ENSURE_SUCCESS(rv, rv);
    if (!imgContainer)
      return NS_ERROR_NOT_AVAILABLE;

    // use the size of the image as the size of the drag image
    imgContainer->GetWidth(&aScreenDragRect->width);
    imgContainer->GetHeight(&aScreenDragRect->height);
  }
  else {
    NS_ASSERTION(aCanvas, "both image and canvas are null");
    nsIntSize sz = aCanvas->GetSize();
    aScreenDragRect->width = sz.width;
    aScreenDragRect->height = sz.height;
  }

  nsIntSize srcSize = aScreenDragRect->Size();
  nsIntSize destSize = srcSize;

  if (destSize.width == 0 || destSize.height == 0)
    return NS_ERROR_FAILURE;

  nsresult result = NS_OK;
  if (aImageLoader) {
    RefPtr<DrawTarget> dt =
      gfxPlatform::GetPlatform()->
        CreateOffscreenContentDrawTarget(destSize,
                                         SurfaceFormat::B8G8R8A8);
    if (!dt || !dt->IsValid())
      return NS_ERROR_FAILURE;

    RefPtr<gfxContext> ctx = gfxContext::CreateOrNull(dt);
    if (!ctx)
      return NS_ERROR_FAILURE;

    DrawResult res =
      imgContainer->Draw(ctx, destSize, ImageRegion::Create(destSize),
                         imgIContainer::FRAME_CURRENT,
                         SamplingFilter::GOOD, /* no SVGImageContext */ Nothing(),
                         imgIContainer::FLAG_SYNC_DECODE);
    if (res == DrawResult::BAD_IMAGE || res == DrawResult::BAD_ARGS) {
      return NS_ERROR_FAILURE;
    }
    *aSurface = dt->Snapshot();
  } else {
    *aSurface = aCanvas->GetSurfaceSnapshot();
  }

  return result;
}

void
nsBaseDragService::ConvertToUnscaledDevPixels(nsPresContext* aPresContext,
                                              int32_t* aScreenX, int32_t* aScreenY)
{
  int32_t adj = aPresContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom();
  *aScreenX = nsPresContext::CSSPixelsToAppUnits(*aScreenX) / adj;
  *aScreenY = nsPresContext::CSSPixelsToAppUnits(*aScreenY) / adj;
}

NS_IMETHODIMP
nsBaseDragService::Suppress()
{
  EndDragSession(false);
  ++mSuppressLevel;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::Unsuppress()
{
  --mSuppressLevel;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::UserCancelled()
{
  mUserCancelled = true;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::UpdateDragEffect()
{
  mDragActionFromChildProcess = mDragAction;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::DragEventDispatchedToChildProcess()
{
  mDragEventDispatchedToChildProcess = true;
  return NS_OK;
}

bool
nsBaseDragService::MaybeAddChildProcess(mozilla::dom::ContentParent* aChild)
{
  if (!mChildProcesses.Contains(aChild)) {
    mChildProcesses.AppendElement(aChild);
    return true;
  }
  return false;
}