Bug 343430. Reduce the area we scroll on Windows to reduce flicker by excluding areas that shouldn't be moving. On Linux, since we can't control the area we scroll, just disable accelerated scrolling in that case and repaint everything. r+sr=dbaron

view/src/nsScrollPortView.cpp

@@ -578,9 +578,33 @@ void nsScrollPortView::Scroll(nsView *aScrolledView, nsPoint aTwipsDelta, nsPoin
       // consistent with the view hierarchy.
       mViewManager->UpdateView(this, 0);
     } else { // if we can blit and have a scrollwidget then scroll.
+      nsRect* toScrollPtr = nsnull;
+
+#ifdef XP_WIN
+      nsRect toScroll;
+      if (!updateRegion.IsEmpty()) {
+        nsRegion regionToScroll;
+        regionToScroll.Sub(nsRect(nsPoint(0,0), GetBounds().Size()),
+                           updateRegion);
+        nsRegionRectIterator iter(regionToScroll);
+        nsRect biggestRect(0,0,0,0);
+        const nsRect* r;
+        for (r = iter.Next(); r; r = iter.Next()) {
+          if (r->width*r->height > biggestRect.width*biggestRect.height) {
+            biggestRect = *r;
+          }
+        }
+        regionToScroll.Sub(regionToScroll, biggestRect);
+        updateRegion.Or(updateRegion, regionToScroll);
+        toScrollPtr = &toScroll;
+        toScroll = biggestRect;
+        toScroll.ScaleRoundOut(1.0/aP2A);
+      }
+#endif
+
       // Scroll the contents of the widget by the specified amount, and scroll
       // the child widgets
-      scrollWidget->Scroll(aPixDelta.x, aPixDelta.y, nsnull);
+      scrollWidget->Scroll(aPixDelta.x, aPixDelta.y, toScrollPtr);
       mViewManager->UpdateViewAfterScroll(this, updateRegion);
     }
   }

view/src/nsViewManager.cpp

@@ -1628,8 +1628,12 @@ PRBool nsViewManager::CanScrollWithBitBlt(nsView* aView, nsPoint aDelta,
 
   aUpdateRegion->MoveBy(-displayOffset);
 
+#ifdef MOZ_WIDGET_GTK2
+  return aUpdateRegion->IsEmpty();
+#else
   return PR_TRUE;
-}                                            
+#endif
+}
 
 NS_IMETHODIMP nsViewManager::SetViewCheckChildEvents(nsIView *aView, PRBool aEnable)
 {

widget/src/windows/nsWindow.cpp

@@ -3278,7 +3278,7 @@ NS_METHOD nsWindow::Scroll(PRInt32 aDx, PRInt32 aDy, nsRect *aClipRect)
     trect.bottom = aClipRect->YMost();
   }
 
-  ::ScrollWindowEx(mWnd, aDx, aDy, (nsnull != aClipRect) ? &trect : NULL, NULL,
+  ::ScrollWindowEx(mWnd, aDx, aDy, NULL, (nsnull != aClipRect) ? &trect : NULL,
                    NULL, NULL, SW_INVALIDATE | SW_SCROLLCHILDREN);
   ::UpdateWindow(mWnd);
   return NS_OK;