gecko-dev/widget/nsBaseDragService.cpp

/* -*- 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 "nsArrayUtils.h"
#include "nsIServiceManager.h"
#include "nsITransferable.h"
#include "nsSize.h"
#include "nsXPCOM.h"
#include "nsISupportsPrimitives.h"
#include "nsCOMPtr.h"
#include "nsIInterfaceRequestorUtils.h"
#include "nsIFrame.h"
#include "nsFrameLoaderOwner.h"
#include "mozilla/dom/Document.h"
#include "nsIContent.h"
#include "nsViewManager.h"
#include "nsINode.h"
#include "nsPresContext.h"
#include "nsIImageLoadingContent.h"
#include "imgIContainer.h"
#include "imgIRequest.h"
#include "ImageRegion.h"
#include "nsQueryObject.h"
#include "nsRegion.h"
#include "nsXULPopupManager.h"
#include "nsMenuPopupFrame.h"
#include "SVGImageContext.h"
#ifdef MOZ_XUL
#  include "nsTreeBodyFrame.h"
#endif
#include "mozilla/MouseEvents.h"
#include "mozilla/Preferences.h"
#include "mozilla/PresShell.h"
#include "mozilla/dom/BindingDeclarations.h"
#include "mozilla/dom/DataTransferItemList.h"
#include "mozilla/dom/DataTransfer.h"
#include "mozilla/dom/DragEvent.h"
#include "mozilla/dom/MouseEventBinding.h"
#include "mozilla/dom/Selection.h"
#include "mozilla/gfx/2D.h"
#include "mozilla/Unused.h"
#include "nsFrameLoader.h"
#include "BrowserParent.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),
      mContentPolicyType(nsIContentPolicy::TYPE_OTHER),
      mSuppressLevel(0),
      mInputSource(MouseEvent_Binding::MOZ_SOURCE_MOUSE) {}

nsBaseDragService::~nsBaseDragService() = default;

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::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(Document** 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(nsINode** aSourceNode) {
  *aSourceNode = do_AddRef(mSourceNode).take();
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::GetTriggeringPrincipal(nsIPrincipal** aPrincipal) {
  NS_IF_ADDREF(*aPrincipal = mTriggeringPrincipal);
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::SetTriggeringPrincipal(nsIPrincipal* aPrincipal) {
  mTriggeringPrincipal = aPrincipal;
  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::GetDataTransferXPCOM(DataTransfer** aDataTransfer) {
  *aDataTransfer = mDataTransfer;
  NS_IF_ADDREF(*aDataTransfer);
  return NS_OK;
}

NS_IMETHODIMP
nsBaseDragService::SetDataTransferXPCOM(DataTransfer* aDataTransfer) {
  NS_ENSURE_STATE(aDataTransfer);
  mDataTransfer = aDataTransfer;
  return NS_OK;
}

DataTransfer* nsBaseDragService::GetDataTransfer() { return mDataTransfer; }

void nsBaseDragService::SetDataTransfer(DataTransfer* aDataTransfer) {
  mDataTransfer = aDataTransfer;
}

//-------------------------------------------------------------------------
NS_IMETHODIMP
nsBaseDragService::InvokeDragSession(
    nsINode* aDOMNode, nsIPrincipal* aPrincipal, nsIArray* aTransferableArray,
    uint32_t aActionType,
    nsContentPolicyType aContentPolicyType = nsIContentPolicy::TYPE_OTHER) {
  AUTO_PROFILER_LABEL("nsBaseDragService::InvokeDragSession", OTHER);

  // If you're hitting this, a test is causing the browser to attempt to enter
  // the drag-drop native nested event loop, which will put the browser in a
  // state that won't run tests properly until there's manual intervention
  // to exit the drag-drop loop (either by moving the mouse or hitting escape),
  // which can't be done from script since we're in the nested loop.
  //
  // The best way to avoid this is to catch the dragstart event on the item
  // being dragged, and then to call preventDefault() and stopPropagating() on
  // it. Alternatively, use EventUtils.synthesizeDragStart, which will do this
  // for you.
  if (XRE_IsParentProcess()) {
    MOZ_ASSERT(
        !xpc::IsInAutomation(),
        "About to start drag-drop native loop on which will prevent later "
        "tests from running properly.");
  }

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

  // stash the document of the dom node
  mSourceDocument = aDOMNode->OwnerDoc();
  mTriggeringPrincipal = aPrincipal;
  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.
  PresShell::ClearMouseCapture(nullptr);

  uint32_t length = 0;
  mozilla::Unused << aTransferableArray->GetLength(&length);
  for (uint32_t i = 0; i < length; ++i) {
    nsCOMPtr<nsITransferable> trans = do_QueryElementAt(aTransferableArray, i);
    if (trans) {
      // Set the requestingPrincipal on the transferable.
      trans->SetRequestingPrincipal(mSourceNode->NodePrincipal());
      trans->SetContentPolicyType(mContentPolicyType);
    }
  }

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

  if (NS_FAILED(rv)) {
    // Set mDoingDrag so that EndDragSession cleans up and sends the dragend
    // event after the aborted drag.
    mDoingDrag = true;
    EndDragSession(true, 0);
  }

  return rv;
}

NS_IMETHODIMP
nsBaseDragService::InvokeDragSessionWithImage(
    nsINode* aDOMNode, nsIPrincipal* aPrincipal, nsIArray* aTransferableArray,
    uint32_t aActionType, nsINode* aImage, int32_t aImageX, int32_t aImageY,
    DragEvent* aDragEvent, DataTransfer* 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);
  mDragStartData = nullptr;

  mScreenPosition.x = aDragEvent->ScreenX(CallerType::System);
  mScreenPosition.y = aDragEvent->ScreenY(CallerType::System);
  mInputSource = aDragEvent->MozInputSource();

  // If dragging within a XUL tree and no custom drag image was
  // set, the region argument to InvokeDragSessionWithImage needs
  // to be set to the area encompassing the selected rows of the
  // tree to ensure that the drag feedback gets clipped to those
  // rows. For other content, region should be null.
  mRegion = Nothing();
#ifdef MOZ_XUL
  if (aDOMNode && aDOMNode->IsContent() && !aImage) {
    if (aDOMNode->NodeInfo()->Equals(nsGkAtoms::treechildren,
                                     kNameSpaceID_XUL)) {
      nsTreeBodyFrame* treeBody =
          do_QueryFrame(aDOMNode->AsContent()->GetPrimaryFrame());
      if (treeBody) {
        mRegion = treeBody->GetSelectionRegion();
      }
    }
  }
#endif

  nsresult rv =
      InvokeDragSession(aDOMNode, aPrincipal, aTransferableArray, aActionType,
                        nsIContentPolicy::TYPE_INTERNAL_IMAGE);
  mRegion = Nothing();
  return rv;
}

NS_IMETHODIMP
nsBaseDragService::InvokeDragSessionWithRemoteImage(
    nsINode* aDOMNode, nsIPrincipal* aPrincipal, nsIArray* aTransferableArray,
    uint32_t aActionType, RemoteDragStartData* aDragStartData,
    DragEvent* aDragEvent, DataTransfer* 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 = nullptr;
  mDragStartData = aDragStartData;
  mImageOffset = CSSIntPoint(0, 0);

  mScreenPosition.x = aDragEvent->ScreenX(CallerType::System);
  mScreenPosition.y = aDragEvent->ScreenY(CallerType::System);
  mInputSource = aDragEvent->MozInputSource();

  nsresult rv =
      InvokeDragSession(aDOMNode, aPrincipal, aTransferableArray, aActionType,
                        nsIContentPolicy::TYPE_INTERNAL_IMAGE);
  mRegion = Nothing();
  return rv;
}

NS_IMETHODIMP
nsBaseDragService::InvokeDragSessionWithSelection(Selection* aSelection,
                                                  nsIPrincipal* aPrincipal,
                                                  nsIArray* aTransferableArray,
                                                  uint32_t aActionType,
                                                  DragEvent* aDragEvent,
                                                  DataTransfer* 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();
  mDragStartData = nullptr;
  mRegion = Nothing();

  mScreenPosition.x = aDragEvent->ScreenX(CallerType::System);
  mScreenPosition.y = aDragEvent->ScreenY(CallerType::System);
  mInputSource = aDragEvent->MozInputSource();

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

  return InvokeDragSession(node, aPrincipal, aTransferableArray, aActionType,
                           nsIContentPolicy::TYPE_OTHER);
}

//-------------------------------------------------------------------------
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, mScreenPosition.x - mImageOffset.x,
                            mScreenPosition.y - 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, uint32_t aKeyModifiers) {
  if (!mDoingDrag) {
    return NS_ERROR_FAILURE;
  }

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

  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, aKeyModifiers);
    // Continue sending input events with input priority when stopping the dnd
    // session.
    mChildProcesses[i]->SetInputPriorityEventEnabled(true);
  }
  mChildProcesses.Clear();

  // mDataTransfer and the items it owns are going to die anyway, but we
  // explicitly deref the contained data here so that we don't have to wait for
  // CC to reclaim the memory.
  if (XRE_IsParentProcess()) {
    DiscardInternalTransferData();
  }

  mDoingDrag = false;
  mCanDrop = false;

  // release the source we've been holding on to.
  mSourceDocument = nullptr;
  mSourceNode = nullptr;
  mTriggeringPrincipal = nullptr;
  mSelection = nullptr;
  mDataTransfer = nullptr;
  mHasImage = false;
  mUserCancelled = false;
  mDragPopup = nullptr;
  mDragStartData = nullptr;
  mImage = nullptr;
  mImageOffset = CSSIntPoint();
  mScreenPosition = CSSIntPoint();
  mEndDragPoint = LayoutDeviceIntPoint(0, 0);
  mInputSource = MouseEvent_Binding::MOZ_SOURCE_MOUSE;
  mRegion = Nothing();

  return NS_OK;
}

void nsBaseDragService::DiscardInternalTransferData() {
  if (mDataTransfer && mSourceNode) {
    MOZ_ASSERT(mDataTransfer);

    DataTransferItemList* items = mDataTransfer->Items();
    for (size_t i = 0; i < items->Length(); i++) {
      bool found;
      DataTransferItem* item = items->IndexedGetter(i, found);

      // Non-OTHER items may still be needed by JS. Skip them.
      if (!found || item->Kind() != DataTransferItem::KIND_OTHER) {
        continue;
      }

      nsCOMPtr<nsIVariant> variant = item->DataNoSecurityCheck();
      nsCOMPtr<nsIWritableVariant> writable = do_QueryInterface(variant);

      if (writable) {
        writable->SetAsEmpty();
      }
    }
  }
}

NS_IMETHODIMP
nsBaseDragService::FireDragEventAtSource(EventMessage aEventMessage,
                                         uint32_t aKeyModifiers) {
  if (mSourceNode && mSourceDocument && !mSuppressLevel) {
    RefPtr<PresShell> presShell = mSourceDocument->GetPresShell();
    if (presShell) {
      nsEventStatus status = nsEventStatus_eIgnore;
      WidgetDragEvent event(true, aEventMessage, nullptr);
      event.mInputSource = mInputSource;
      if (aEventMessage == eDragEnd) {
        event.mRefPoint = mEndDragPoint;
        event.mUserCancelled = mUserCancelled;
      }
      event.mModifiers = aKeyModifiers;
      // 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->IsMenuPopupFrame()) {
      CSSIntPoint cssPos =
          RoundedToInt(LayoutDeviceIntPoint(aX, aY) /
                       frame->PresContext()->CSSToDevPixelScale()) -
          mImageOffset;
      (static_cast<nsMenuPopupFrame*>(frame))->MoveTo(cssPos, true);
    }
  }

  return NS_OK;
}

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

  RefPtr<Document> document = content->GetComposedDoc();
  if (document) {
    document->FlushPendingNotifications(FlushType::Display);
    return document->GetPresShell();
  }

  return nullptr;
}

nsresult nsBaseDragService::DrawDrag(nsINode* aDOMNode,
                                     const Maybe<CSSIntRegion>& aRegion,
                                     CSSIntPoint aScreenPosition,
                                     LayoutDeviceIntRect* aScreenDragRect,
                                     RefPtr<SourceSurface>* aSurface,
                                     nsPresContext** aPresContext) {
  *aSurface = nullptr;
  *aPresContext = nullptr;

  // use a default size, in case of an error.
  aScreenDragRect->SetRect(aScreenPosition.x - mImageOffset.x,
                           aScreenPosition.y - mImageOffset.y, 1, 1);

  // if a drag image was specified, use that, otherwise, use the source node
  nsCOMPtr<nsINode> 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
  PresShell* presShell = GetPresShellForContent(dragNode);
  if (!presShell && mImage) {
    presShell = GetPresShellForContent(aDOMNode);
  }
  if (!presShell) {
    return NS_ERROR_FAILURE;
  }

  *aPresContext = presShell->GetPresContext();

  if (mDragStartData) {
    if (mImage) {
      // Just clear the surface if chrome has overridden it with an image.
      *aSurface = nullptr;
    } else {
      *aSurface = mDragStartData->TakeVisualization(aScreenDragRect);
    }

    mDragStartData = nullptr;
    return NS_OK;
  }

  // convert mouse position to dev pixels of the prescontext
  CSSIntPoint screenPosition(aScreenPosition);
  screenPosition.x -= mImageOffset.x;
  screenPosition.y -= mImageOffset.y;
  LayoutDeviceIntPoint screenPoint =
      ConvertToUnscaledDevPixels(*aPresContext, screenPosition);
  aScreenDragRect->MoveTo(screenPoint.x, screenPoint.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
    CSSIntRect dragRect;
    if (aRegion) {
      // the region's coordinates are relative to the root frame
      dragRect = aRegion->GetBounds();

      nsIFrame* rootFrame = presShell->GetRootFrame();
      CSSIntRect screenRect = rootFrame->GetScreenRect();
      dragRect.MoveBy(screenRect.TopLeft());
    } 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) {
        dragRect = frame->GetScreenRect();
      }
    }

    nsIntRect dragRectDev =
        ToAppUnits(dragRect, AppUnitsPerCSSPixel())
            .ToOutsidePixels((*aPresContext)->AppUnitsPerDevPixel());
    aScreenDragRect->SizeTo(dragRectDev.Width(), dragRectDev.Height());
    return NS_OK;
  }

  // draw the image for selections
  if (mSelection) {
    LayoutDeviceIntPoint pnt(aScreenDragRect->TopLeft());
    *aSurface = presShell->RenderSelection(
        mSelection, pnt, aScreenDragRect,
        mImage ? RenderImageFlags::None : RenderImageFlags::AutoScale);
    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::FromNodeOrNull(content);
    if (canvas) {
      return DrawDragForImage(*aPresContext, nullptr, canvas, aScreenDragRect,
                              aSurface);
    }

    nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(dragNode);
    // for image nodes, create the drag image from the actual image data
    if (imageLoader) {
      return DrawDragForImage(*aPresContext, imageLoader, nullptr,
                              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->IsMenuPopupFrame()) {
      mDragPopup = content;
    }
  }

  if (!mDragPopup) {
    // otherwise, just draw the node
    RenderImageFlags renderFlags =
        mImage ? RenderImageFlags::None : RenderImageFlags::AutoScale;
    if (renderFlags != RenderImageFlags::None) {
      // check if the dragged node itself is an img element
      if (dragNode->NodeName().LowerCaseEqualsLiteral("img")) {
        renderFlags = renderFlags | RenderImageFlags::IsImage;
      } else {
        nsINodeList* childList = dragNode->ChildNodes();
        uint32_t length = childList->Length();
        // check every childnode for being an img element
        // XXXbz why don't we need to check descendants recursively?
        for (uint32_t count = 0; count < length; ++count) {
          if (childList->Item(count)->NodeName().LowerCaseEqualsLiteral(
                  "img")) {
            // if the dragnode contains an image, set RenderImageFlags::IsImage
            // flag
            renderFlags = renderFlags | RenderImageFlags::IsImage;
            break;
          }
        }
      }
    }
    LayoutDeviceIntPoint pnt(aScreenDragRect->TopLeft());
    *aSurface = presShell->RenderNode(dragNode, aRegion, pnt, aScreenDragRect,
                                      renderFlags);
  }

  // If an image was specified, reset the position from the offset that was
  // supplied.
  if (mImage) {
    aScreenDragRect->MoveTo(screenPoint.x, screenPoint.y);
  }

  return NS_OK;
}

nsresult nsBaseDragService::DrawDragForImage(
    nsPresContext* aPresContext, nsIImageLoadingContent* aImageLoader,
    HTMLCanvasElement* aCanvas, LayoutDeviceIntRect* 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
    int32_t imageWidth, imageHeight;
    rv = imgContainer->GetWidth(&imageWidth);
    NS_ENSURE_SUCCESS(rv, rv);

    rv = imgContainer->GetHeight(&imageHeight);
    NS_ENSURE_SUCCESS(rv, rv);

    aScreenDragRect->SizeTo(aPresContext->CSSPixelsToDevPixels(imageWidth),
                            aPresContext->CSSPixelsToDevPixels(imageHeight));
  } else {
    // XXX The canvas size should be converted to dev pixels.
    NS_ASSERTION(aCanvas, "both image and canvas are null");
    nsIntSize sz = aCanvas->GetSize();
    aScreenDragRect->SizeTo(sz.width, sz.height);
  }

  nsIntSize destSize;
  destSize.width = aScreenDragRect->Width();
  destSize.height = aScreenDragRect->Height();
  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;

    ImgDrawResult res =
        imgContainer->Draw(ctx, destSize, ImageRegion::Create(destSize),
                           imgIContainer::FRAME_CURRENT, SamplingFilter::GOOD,
                           /* no SVGImageContext */ Nothing(),
                           imgIContainer::FLAG_SYNC_DECODE, 1.0);
    if (res == ImgDrawResult::BAD_IMAGE || res == ImgDrawResult::BAD_ARGS ||
        res == ImgDrawResult::NOT_SUPPORTED) {
      return NS_ERROR_FAILURE;
    }
    *aSurface = dt->Snapshot();
  } else {
    *aSurface = aCanvas->GetSurfaceSnapshot();
  }

  return result;
}

LayoutDeviceIntPoint nsBaseDragService::ConvertToUnscaledDevPixels(
    nsPresContext* aPresContext, CSSIntPoint aScreenPosition) {
  int32_t adj =
      aPresContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom();
  return LayoutDeviceIntPoint(
      nsPresContext::CSSPixelsToAppUnits(aScreenPosition.x) / adj,
      nsPresContext::CSSPixelsToAppUnits(aScreenPosition.y) / adj);
}

NS_IMETHODIMP
nsBaseDragService::Suppress() {
  EndDragSession(false, 0);
  ++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::UpdateDragImage(nsINode* aImage, int32_t aImageX,
                                   int32_t aImageY) {
  // Don't change the image if this is a drag from another source or if there
  // is a drag popup.
  if (!mSourceNode || mDragPopup) return NS_OK;

  mImage = aImage;
  mImageOffset = CSSIntPoint(aImageX, aImageY);
  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;
}