Bug 1280324, part 1 - Add functionality to the PrintTarget sub-classes to return reference DrawTargets. r=edwin

gfx/thebes/PrintTarget.cpp

@@ -75,6 +75,36 @@ PrintTarget::MakeDrawTarget(const IntSize& aSize,
   return dt.forget();
 }
 
+already_AddRefed<DrawTarget>
+PrintTarget::GetReferenceDrawTarget()
+{
+  if (!mRefDT) {
+    IntSize size(1, 1);
+
+    cairo_surface_t* surface =
+      cairo_surface_create_similar(mCairoSurface,
+                                   cairo_surface_get_content(mCairoSurface),
+                                   size.width, size.height);
+
+    if (cairo_surface_status(surface)) {
+      return nullptr;
+    }
+
+    RefPtr<DrawTarget> dt =
+      Factory::CreateDrawTargetForCairoSurface(surface, size);
+
+    // The DT addrefs the surface, so we need drop our own reference to it:
+    cairo_surface_destroy(surface);
+
+    if (!dt || !dt->IsValid()) {
+      return nullptr;
+    }
+
+    mRefDT = dt.forget();
+  }
+  return do_AddRef(mRefDT);
+}
+
 already_AddRefed<DrawTarget>
 PrintTarget::CreateRecordingDrawTarget(DrawEventRecorder* aRecorder,
                                        DrawTarget* aDrawTarget)

gfx/thebes/PrintTarget.h

@@ -111,6 +111,14 @@ public:
   MakeDrawTarget(const IntSize& aSize,
                  DrawEventRecorder* aRecorder = nullptr);
 
+  /**
+   * Returns a reference DrawTarget. Unlike MakeDrawTarget, this method is not
+   * restricted to being called between BeginPage()/EndPage() calls, and the
+   * returned DrawTarget it is still valid to use after EndPage() has been
+   * called.
+   */
+  virtual already_AddRefed<DrawTarget> GetReferenceDrawTarget();
+
 protected:
 
   // Only created via subclass's constructors
@@ -124,6 +132,7 @@ protected:
                             DrawTarget* aDrawTarget);
 
   cairo_surface_t* mCairoSurface;
+  RefPtr<DrawTarget> mRefDT; // reference DT
   IntSize mSize;
   bool mIsFinished;
 };

gfx/thebes/PrintTargetThebes.cpp

@@ -52,6 +52,20 @@ PrintTargetThebes::MakeDrawTarget(const IntSize& aSize,
   return dt.forget();
 }
 
+already_AddRefed<DrawTarget>
+PrintTargetThebes::GetReferenceDrawTarget()
+{
+  if (!mRefDT) {
+    RefPtr<gfx::DrawTarget> dt =
+      gfxPlatform::GetPlatform()->CreateDrawTargetForSurface(mGfxSurface, mSize);
+    if (!dt || !dt->IsValid()) {
+      return nullptr;
+    }
+    mRefDT = dt->CreateSimilarDrawTarget(IntSize(1,1), dt->GetFormat());
+  }
+  return do_AddRef(mRefDT);
+}
+
 nsresult
 PrintTargetThebes::BeginPrinting(const nsAString& aTitle,
                                  const nsAString& aPrintToFileName)

gfx/thebes/PrintTargetThebes.h

@@ -41,6 +41,8 @@ public:
   MakeDrawTarget(const IntSize& aSize,
                  DrawEventRecorder* aRecorder = nullptr) override;
 
+  virtual already_AddRefed<DrawTarget> GetReferenceDrawTarget() final;
+
 private:
 
   // Only created via CreateOrNull