Bug 1475139 part 12 - Expose drawSnapshot API to <browser>. r=nika

This commit initially exposes the drawSnapshot API off of <browser>. This
is done by adding a WebIDL binding to FrameLoader and wrapping it in
browser.xml.

Differential Revision: https://phabricator.services.mozilla.com/D6791

--HG--
extra : rebase_source : 9f819b13c102edf42ab2bb2466578751a7a2f647

dom/base/nsFrameLoader.cpp

@@ -80,8 +80,11 @@
 #include "mozilla/dom/ChromeMessageSender.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/FrameLoaderBinding.h"
+#include "mozilla/gfx/CrossProcessPaint.h"
 #include "mozilla/jsipc/CrossProcessObjectWrappers.h"
 #include "mozilla/layout/RenderFrameParent.h"
+#include "mozilla/ServoCSSParser.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsGenericHTMLFrameElement.h"
 #include "GeckoProfiler.h"
 
@@ -3103,6 +3106,64 @@ nsFrameLoader::Print(uint64_t aOuterWindowID,
 #endif
 }
 
+already_AddRefed<mozilla::dom::Promise>
+nsFrameLoader::DrawSnapshot(double aX,
+                            double aY,
+                            double aW,
+                            double aH,
+                            double aScale,
+                            const nsAString& aBackgroundColor,
+                            mozilla::ErrorResult& aRv)
+{
+  RefPtr<nsIGlobalObject> global = GetOwnerContent()->GetOwnerGlobal();
+  RefPtr<Promise> promise = Promise::Create(global, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  RefPtr<nsIDocument> document = GetOwnerContent()->GetOwnerDocument();
+  if (NS_WARN_IF(!document)) {
+    aRv = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+  nsIPresShell* presShell = document->GetShell();
+  if (NS_WARN_IF(!presShell)) {
+    aRv = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+
+  nscolor color;
+  css::Loader* loader = document->CSSLoader();
+  ServoStyleSet* set = presShell->StyleSet();
+  if (NS_WARN_IF(!ServoCSSParser::ComputeColor(set,
+                                               NS_RGB(0, 0, 0),
+                                               aBackgroundColor,
+                                               &color,
+                                               nullptr,
+                                               loader))) {
+    aRv = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+
+  gfx::IntRect rect = gfx::IntRect::RoundOut(gfx::Rect(aX, aY, aW, aH));
+
+  if (IsRemoteFrame()) {
+    gfx::CrossProcessPaint::StartRemote(mRemoteBrowser->GetTabId(),
+                                        rect,
+                                        aScale,
+                                        color,
+                                        promise);
+  } else {
+    gfx::CrossProcessPaint::StartLocal(mDocShell,
+                                       rect,
+                                       aScale,
+                                       color,
+                                       promise);
+  }
+
+  return promise.forget();
+}
+
 already_AddRefed<nsITabParent>
 nsFrameLoader::GetTabParent()
 {

dom/base/nsFrameLoader.h

@@ -171,6 +171,15 @@ public:
              nsIWebProgressListener* aProgressListener,
              mozilla::ErrorResult& aRv);
 
+  already_AddRefed<mozilla::dom::Promise>
+  DrawSnapshot(double aX,
+               double aY,
+               double aW,
+               double aH,
+               double aScale,
+               const nsAString& aBackgroundColor,
+               mozilla::ErrorResult& aRv);
+
   void StartPersistence(uint64_t aOuterWindowID,
                         nsIWebBrowserPersistDocumentReceiver* aRecv,
                         mozilla::ErrorResult& aRv);

dom/webidl/FrameLoader.webidl

@@ -108,6 +108,30 @@ interface FrameLoader {
              nsIPrintSettings aPrintSettings,
              optional nsIWebProgressListener? aProgressListener = null);
 
+  /**
+   * Renders a region of the frame into an image bitmap.
+   *
+   * @param x
+   * @param y
+   * @param w
+   * @param h Specify the area of the window to render, in CSS
+   * pixels. This is relative to the current scroll position.
+   * @param scale The scale to render the window at. Use devicePixelRatio
+   * to have comparable rendering to the OS.
+   * @param backgroundColor The background color to use.
+   *
+   * This API can only be used in the parent process, as content processes
+   * cannot access the rendering of out of process iframes. This API works
+   * with remote and local frames.
+   */
+  [Throws]
+  Promise<ImageBitmap> drawSnapshot(double x,
+                                    double y,
+                                    double w,
+                                    double h,
+                                    double scale,
+                                    DOMString backgroundColor);
+
   /**
    * If false, then the subdocument is not clipped to its CSS viewport, and the
    * subdocument's viewport scrollbar(s) are not rendered.

toolkit/content/widgets/browser.xml

@@ -1904,6 +1904,24 @@
         </body>
       </method>
 
+      <method name="drawSnapshot">
+        <parameter name="x"/>
+        <parameter name="y"/>
+        <parameter name="w"/>
+        <parameter name="h"/>
+        <parameter name="scale"/>
+        <parameter name="backgroundColor"/>
+        <body>
+          <![CDATA[
+            if (!this.frameLoader) {
+              throw Components.Exception("No frame loader.",
+                                         Cr.NS_ERROR_FAILURE);
+            }
+            return this.frameLoader.drawSnapshot(x, y, w, h, scale, backgroundColor);
+          ]]>
+        </body>
+      </method>
+
       <method name="dropLinks">
         <parameter name="aLinksCount"/>
         <parameter name="aLinks"/>