Create the drag image at target scale factor when possible.

third_party/WebKit/Source/core/page/DragController.cpp

 /*
  * Copyright (C) 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 28 matching lines @@
 #include "core/dom/Text.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/editing/DragCaretController.h"
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/Editor.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/serializers/Serialization.h"
 #include "core/events/TextEvent.h"
 #include "core/fetch/ImageResource.h"
 #include "core/fetch/ResourceFetcher.h"
+#include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLAnchorElement.h"
 #include "core/html/HTMLFormElement.h"
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLPlugInElement.h"
 #include "core/input/EventHandler.h"
 #include "core/layout/LayoutTheme.h"
 #include "core/layout/LayoutView.h"
@@ skipping 710 matching lines @@
 static IntPoint dragLocationForSelectionDrag(LocalFrame* sourceFrame)
 {
     IntRect draggingRect = enclosingIntRect(sourceFrame->selection().bounds());
     int xpos = draggingRect.maxX();
     xpos = draggingRect.x() < xpos ? draggingRect.x() : xpos;
     int ypos = draggingRect.maxY();
     ypos = draggingRect.y() < ypos ? draggingRect.y() : ypos;
     return IntPoint(xpos, ypos);
 }
 
-static const IntSize& maxDragImageSize()
+static const IntSize maxDragImageSize(float deviceScaleFactor)
 {
 #if OS(MACOSX)
     // Match Safari's drag image size.
     static const IntSize maxDragImageSize(400, 400);
 #else
     static const IntSize maxDragImageSize(200, 200);
 #endif
-    return maxDragImageSize;
+    IntSize maxSizeInPixels = maxDragImageSize;
+    maxSizeInPixels.scale(deviceScaleFactor);
+    return maxSizeInPixels;
 }
 
-static PassOwnPtr<DragImage> dragImageForImage(Element* element, Image* image, const IntPoint& dragOrigin, const IntPoint& imageLocation, const IntSize& imageSizeInDIP, IntPoint& dragLocation)
+static PassOwnPtr<DragImage> dragImageForImage(Element* element, Image* image, float deviceScaleFactor, const IntPoint& dragOrigin, const IntPoint& imageElementLocation, const IntSize& imageElementSizeInPixels, IntPoint& dragLocation)
 {
     OwnPtr<DragImage> dragImage;
     IntPoint origin;
 
     InterpolationQuality interpolationQuality = element->ensureComputedStyle()->imageRendering() == ImageRenderingPixelated ? InterpolationNone : InterpolationHigh;
     RespectImageOrientationEnum shouldRespectImageOrientation = LayoutObject::shouldRespectImageOrientation(element->layoutObject());
     ImageOrientation orientation;
 
     if (shouldRespectImageOrientation == RespectImageOrientation && image->isBitmapImage())
         orientation = toBitmapImage(image)->currentFrameOrientation();
 
-    if (image->size().height() * image->size().width() <= MaxOriginalImageArea
+    IntSize imageSize = orientation.usesWidthAsHeight() ? image->size().transposedSize() : image->size();
+
+    FloatSize imageScale = DragImage::clampedImageScale(imageSize, imageElementSizeInPixels, maxDragImageSize(deviceScaleFactor));
+
+    if (imageSize.area() <= MaxOriginalImageArea
         && (dragImage = DragImage::create(image, shouldRespectImageOrientation,
-            1 /* deviceScaleFactor */, interpolationQuality, DragImageAlpha,
-            DragImage::clampedImageScale(orientation.usesWidthAsHeight() ? image->size().transposedSize() : image->size(), imageSizeInDIP, maxDragImageSize())))) {
-        IntSize originalSize = imageSizeInDIP;
-        origin = imageLocation;
+            deviceScaleFactor, interpolationQuality, DragImageAlpha, imageScale))) {
+        IntSize originalSize = imageElementSizeInPixels;
+        origin = imageElementLocation;
 
         IntSize newSize = dragImage->size();
 
         // Properly orient the drag image and orient it differently if it's smaller than the original
         float scale = newSize.width() / (float)originalSize.width();
         float dx = origin.x() - dragOrigin.x();
         dx *= scale;
         origin.setX((int)(dx + 0.5));
         float dy = origin.y() - dragOrigin.y();
         dy *= scale;
@@ skipping 59 matching lines @@
             return false;
         Element* element = toElement(node);
         Image* image = getImage(element);
         if (!image || image->isNull())
             return false;
         // We shouldn't be starting a drag for an image that can't provide an extension.
         // This is an early detection for problems encountered later upon drop.
         ASSERT(!image->filenameExtension().isEmpty());
         if (!dragImage) {
             const IntRect& imageRect = hitTestResult.imageRect();
-            const IntSize& imageSizeInDIP = src->page()->chromeClient().viewportToScreen(imageRect).size();
+            IntSize imageSizeInPixels = imageRect.size();
+            // TODO(oshima): Remove this scaling and simply pass imageRect to dragImageForImage
+            // once all platforms are migrated to use zoom for dsf.
+            imageSizeInPixels.scale(src->host()->deviceScaleFactor());

[oshima, 2016/01/27 19:01:09]

This is same as what LocalFrame is doing here:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+
+            float screenDeviceScaleFactor = src->page()->chromeClient().screenInfo().deviceScaleFactor;
             // Pass the selected image size in DIP becasue dragImageForImage clips the image in DIP.
             // The coordinates of the locations are in Viewport coordinates, and they're converted in the Blink client.
             // TODO(oshima): Currently, the dragged image on high DPI is scaled and can be blurry because of this.
             // Consider to clip in the screen coordinates to use high resolution image on high DPI screens.
-            dragImage = dragImageForImage(element, image, dragOrigin, imageRect.location(), imageSizeInDIP, dragLocation);
+            dragImage = dragImageForImage(element, image, screenDeviceScaleFactor, dragOrigin, imageRect.location(), imageSizeInPixels, dragLocation);
         }
         doSystemDrag(dragImage.get(), dragLocation, dragOrigin, dataTransfer, src, false);
     } else if (state.m_dragType == DragSourceActionLink) {
         if (linkURL.isEmpty())
             return false;
         if (src->selection().isCaret() && src->selection().isContentEditable()) {
             // a user can initiate a drag on a link without having any text
             // selected.  In this case, we should expand the selection to
             // the enclosing anchor element
             if (Node* node = enclosingAnchorElement(src->selection().base()))
@@ skipping 63 matching lines @@
 
 DEFINE_TRACE(DragController)
 {
     visitor->trace(m_page);
     visitor->trace(m_documentUnderMouse);
     visitor->trace(m_dragInitiator);
     visitor->trace(m_fileInputElementUnderMouse);
 }
 
 } // namespace blink