Creating PNG images from web content to be used by OverviewMode navigation

athena/content/content_proxy.cc

Index: athena/content/content_proxy.cc
diff --git a/athena/content/content_proxy.cc b/athena/content/content_proxy.cc
index a63aa35ed08ddf20da32a8e2ab0e3595d071db28..7dce0e9266ec0ede53b7d2f90095e9215afa6245 100644
--- a/athena/content/content_proxy.cc
+++ b/athena/content/content_proxy.cc
@@ -6,32 +6,74 @@
 
 #include "athena/activity/public/activity.h"
 #include "athena/activity/public/activity_view_model.h"
+#include "base/bind.h"
+#include "base/threading/worker_pool.h"
+#include "content/public/browser/render_view_host.h"
+#include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "ui/aura/window.h"
-#include "ui/views/background.h"
+#include "ui/gfx/codec/png_codec.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/image/image.h"
+#include "ui/gfx/image/image_png_rep.h"
 #include "ui/views/controls/webview/webview.h"
 #include "ui/views/widget/widget.h"
 
 namespace athena {
 
+// Encodes an A8 SkBitmap to grayscale PNG in a worker thread.
+class ProxyImageData : public base::RefCountedThreadSafe<ProxyImageData> {
+ public:
+  ProxyImageData() {
+  }
+
+  void EncodeImage(const SkBitmap& bitmap, base::Closure callback) {
+    if (!base::WorkerPool::PostTaskAndReply(FROM_HERE,
+            base::Bind(&ProxyImageData::EncodeOnWorker,
+                       this,
+                       bitmap),
+            callback,
+            true)) {
+      // When coming here, the resulting image will be empty.
+      DCHECK(false) << "Cannot start bitmap encode task.";
+      callback.Run();
+    }
+  }
+
+  scoped_refptr<base::RefCountedBytes> data() const { return data_; }
+
+ private:
+  friend class base::RefCountedThreadSafe<ProxyImageData>;
+  virtual ~ProxyImageData() {
+  }
+
+  void EncodeOnWorker(const SkBitmap& bitmap) {
+    DCHECK_EQ(bitmap.colorType(), kAlpha_8_SkColorType);
+    // Encode the A8 bitmap to grayscale PNG treating alpha as color intensity.
+    std::vector<unsigned char> data;
+    if (gfx::PNGCodec::EncodeA8SkBitmap(bitmap, &data))
+      data_ = new base::RefCountedBytes(data);
+  }
+
+  scoped_refptr<base::RefCountedBytes> data_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProxyImageData);
+};
+
 ContentProxy::ContentProxy(views::WebView* web_view, Activity* activity)
     : web_view_(web_view),
-      window_(activity->GetWindow()),
-      background_color_(
-          activity->GetActivityViewModel()->GetRepresentativeColor()),
-      content_loaded_(true) {
+      content_visible_(true),
+      content_loaded_(true),
+      content_creation_called_(false),
+      proxy_content_to_image_factory_(this) {
+  // Note: The content will be hidden once the image got created.
   CreateProxyContent();
-  HideOriginalContent();
 }
 
 ContentProxy::~ContentProxy() {
   // If we still have a connection to the original Activity, we make it visible
   // again.
   ShowOriginalContent();
-  // At this point we should either have no view - or the view should not be
-  // shown by its parent anymore.
-  DCHECK(!proxy_content_.get() || !proxy_content_->parent());
-  proxy_content_.reset();
 }
 
 void ContentProxy::ContentWillUnload() {
@@ -39,39 +81,33 @@ void ContentProxy::ContentWillUnload() {
 }
 
 gfx::ImageSkia ContentProxy::GetContentImage() {
-  // For the time being we keep this here and return an empty image.
-  return image_;
+  // While we compress to PNG, we use the original read back.
+  if (!raw_image_.isNull() || !png_data_.get())
+    return raw_image_;
+
+  // Otherwise we convert the PNG.
+  std::vector<gfx::ImagePNGRep> image_reps;
+  image_reps.push_back(gfx::ImagePNGRep(png_data_, 0.0f));
+  return *(gfx::Image(image_reps).ToImageSkia());
 }
 
 void ContentProxy::EvictContent() {
-  HideProxyContent();
-  CreateSolidProxyContent();
-  ShowProxyContent();
+  raw_image_ = gfx::ImageSkia();
+  png_data_->Release();
 }
 
-void ContentProxy::Reparent(aura::Window* new_parent_window) {
-  if (new_parent_window == window_)
-    return;
-
+void ContentProxy::OnPreContentDestroyed() {
   // Since we are breaking now the connection to the old content, we make the
   // content visible again before we continue.
   // Note: Since the owning window is invisible, it does not matter that we
   // make the web content visible if the window gets destroyed shortly after.
   ShowOriginalContent();
 
-  // Transfer the |proxy_content_| to the passed window.
-  window_ = new_parent_window;
   web_view_ = NULL;
-
-  // Move the view to the new window and show it there.
-  HideOriginalContent();
 }
 
 void ContentProxy::ShowOriginalContent() {
-  // Hide our content.
-  HideProxyContent();
-
-  if (web_view_) {
+  if (web_view_ && !content_visible_) {
     // Show the original |web_view_| again.
     web_view_->SetFastResize(false);
     // If the content is loaded, we ask it to relayout itself since the
@@ -81,52 +117,73 @@ void ContentProxy::ShowOriginalContent() {
       web_view_->Layout();
     web_view_->GetWebContents()->GetNativeView()->Show();
     web_view_->SetVisible(true);
+    content_visible_ = true;
   }
 }
 
 void ContentProxy::HideOriginalContent() {
-  if (web_view_) {
+  if (web_view_ && content_visible_) {
     // Hide the |web_view_|.
     // TODO(skuhne): We might consider removing the view from the window while
     // it's hidden - it should work the same way as show/hide and does not have
-    // any window re-ordering effect.
+    // any window re-ordering effect. Furthermore we want possibly to suppress
+    // any resizing of content (not only fast resize) here to avoid jank on
+    // rotation.
     web_view_->GetWebContents()->GetNativeView()->Hide();
     web_view_->SetVisible(false);
     // Don't allow the content to get resized with window size changes.
     web_view_->SetFastResize(true);
+    content_visible_ = false;
   }
-
-  // Show our replacement content.
-  ShowProxyContent();
 }
 
 void ContentProxy::CreateProxyContent() {
-  // For the time being we create only a solid color here.
-  // TODO(skuhne): Replace with copying the drawn content into |proxy_content_|
-  // instead.
-  CreateSolidProxyContent();
-}
+  DCHECK(!content_creation_called_);
+  content_creation_called_ = true;
+  // Unit tests might not have a |web_view_|.
+  if (!web_view_)
+    return;
 
-void ContentProxy::CreateSolidProxyContent() {
-  proxy_content_.reset(new views::View());
-  proxy_content_->set_owned_by_client();
-  proxy_content_->set_background(
-      views::Background::CreateSolidBackground(background_color_));
+  content::RenderViewHost* host =
+      web_view_->GetWebContents()->GetRenderViewHost();
+  DCHECK(host && host->GetView());
+  gfx::Size source = host->GetView()->GetViewBounds().size();
+  gfx::Size target = gfx::Size(source.width() / 2, source.height() / 2);
+  host->CopyFromBackingStore(
+      gfx::Rect(),
+      target,
+      base::Bind(&ContentProxy::OnContentImageRead,
+                 proxy_content_to_image_factory_.GetWeakPtr()),
+      kAlpha_8_SkColorType);
 }
 
-void ContentProxy::ShowProxyContent() {
-  views::Widget* widget = views::Widget::GetWidgetForNativeWindow(window_);
-  DCHECK(widget);
-  views::View* client_view = widget->client_view();
-  // Place the view in front of all others.
-  client_view->AddChildView(proxy_content_.get());
-  proxy_content_->SetSize(client_view->bounds().size());
+void ContentProxy::OnContentImageRead(bool success, const SkBitmap& bitmap) {
+  // Now we can hide the content. Note that after hiding we are freeing memory
+  // and if something goes wrong we will end up with an empty page.
+  HideOriginalContent();
+
+  if (!success || bitmap.empty() || bitmap.isNull())
+    return;
+
+  // While we are encoding the image, we keep the current image as reference
+  // to have something for the overview mode to grab. Once we have the encoded
+  // PNG, we will get rid of this.
+  raw_image_ = gfx::ImageSkia::CreateFrom1xBitmap(bitmap);
+
+  scoped_refptr<ProxyImageData> png_image = new ProxyImageData();
+  png_image->EncodeImage(
+      bitmap,
+      base::Bind(&ContentProxy::OnContentImageEncodeComplete,
+                 proxy_content_to_image_factory_.GetWeakPtr(),
+                 png_image));
 }
 
-void ContentProxy::HideProxyContent() {
-  views::Widget* widget = views::Widget::GetWidgetForNativeWindow(window_);
-  views::View* client_view = widget->client_view();
-  client_view->RemoveChildView(proxy_content_.get());
+void ContentProxy::OnContentImageEncodeComplete(
+    scoped_refptr<ProxyImageData> image) {
+  png_data_ = image->data();
+
+  // From now on we decode the image as needed to save memory.
+  raw_image_ = gfx::ImageSkia();
 }
 
 }  // namespace athena