Plugin Power Saver: Implement srcset syntax for posters.

components/plugins/renderer/webview_plugin.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/plugins/renderer/webview_plugin.h"
 
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/numerics/safe_conversions.h"
 #include "content/public/common/web_preferences.h"
@@ skipping 91 matching lines @@
 
 void WebViewPlugin::RestoreTitleText() {
   if (container_)
     container_->element().setAttribute("title", old_title_);
 }
 
 WebPluginContainer* WebViewPlugin::container() const { return container_; }
 
 bool WebViewPlugin::initialize(WebPluginContainer* container) {
   container_ = container;
-  if (container_)
+  if (container_) {
     old_title_ = container_->element().getAttribute("title");
+
+    // Propagate device scale to inner webview to load the correct resource
+    // when images have a "srcset" attribute.
+    web_view_->setDeviceScaleFactor(container_->deviceScaleFactor());
+  }
   return true;
 }
 
 void WebViewPlugin::destroy() {
   if (delegate_) {
     delegate_->PluginDestroyed();
     delegate_ = NULL;
   }
   container_ = NULL;
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
 NPObject* WebViewPlugin::scriptableObject() { return NULL; }
 
 struct _NPP* WebViewPlugin::pluginNPP() { return NULL; }
 
 bool WebViewPlugin::getFormValue(WebString& value) { return false; }
 
 void WebViewPlugin::paint(WebCanvas* canvas, const WebRect& rect) {
   gfx::Rect paint_rect = gfx::IntersectRects(rect_, rect);
   if (paint_rect.IsEmpty())
     return;
 
   paint_rect.Offset(-rect_.x(), -rect_.y());
 
   canvas->translate(SkIntToScalar(rect_.x()), SkIntToScalar(rect_.y()));
   canvas->save();
 
+  // Before actually painting, remove device scaling, as it would otherwise
+  // be applied twice.
+  web_view_->setDeviceScaleFactor(1);

[jbroman, 2015/03/06 20:25:49]

Changing the device scale factor of the page like this seems wrong (if nothing
else, it forces a style recalc).

Rather, I would think applying a scale by 1/dsf to the canvas (to counter the
one in blink::PageWidgetDelegate::paint) is reasonable.

(In my ideal world, it would be the caller of WebViewImpl::paint that's
responsible for setting up the initial scale, but that's not how things are at
present.)

[tommycli, 2015/03/06 21:30:55]

Done. Okay cool. That's the same thing as bauerb said, so I'm going to go with
that.

+
   web_view_->layout();
   web_view_->paint(canvas, paint_rect);
 
+  // Reapply the container's device scale factor for resource loading.

[tommycli, 2015/03/06 00:19:23]

Not sure if this is actually needed. It doesn't seem to have an effect in my
testing, but it seems like it would be good.

[jbroman, 2015/03/06 20:25:49]

See above.

[tommycli, 2015/03/06 21:30:55]

Done.

+  if (container_)
+    web_view_->setDeviceScaleFactor(container_->deviceScaleFactor());
+
   canvas->restore();
 }
 
 // Coordinates are relative to the containing window.
 void WebViewPlugin::updateGeometry(const WebRect& frame_rect,
                                    const WebRect& clip_rect,
                                    const WebVector<WebRect>& cut_out_rects,
                                    bool is_visible) {
   if (static_cast<gfx::Rect>(frame_rect) != rect_) {
     rect_ = frame_rect;
@@ skipping 87 matching lines @@
 void WebViewPlugin::didClearWindowObject(WebLocalFrame* frame) {
   if (delegate_)
     delegate_->BindWebFrame(frame);
 }
 
 void WebViewPlugin::didReceiveResponse(WebLocalFrame* frame,
                                        unsigned identifier,
                                        const WebURLResponse& response) {
   WebFrameClient::didReceiveResponse(frame, identifier, response);
 }