fixed mask problems when resizing the viewPort while sharing the rend…

…er context

See: http://forum.starling-framework.org/topic/starling-away3d-integration-displayobjectmask-error

starling/src/starling/core/Starling.as

@@ -44,6 +44,7 @@ package starling.core
     import starling.events.TouchProcessor;
     import starling.rendering.Painter;
     import starling.utils.Align;
+    import starling.utils.RectangleUtil;
     import starling.utils.SystemUtil;
 
     /** Dispatched when a new render context is created. The 'data' property references the context. */
@@ -454,29 +455,22 @@ package starling.core
             // the last set viewport is stored in a variable; that way, people can modify the
             // viewPort directly (without a copy) and we still know if it has changed.
 
-            if (forceUpdate ||
-                _previousViewPort.width  != _viewPort.width  ||
-                _previousViewPort.height != _viewPort.height ||
-                _previousViewPort.x != _viewPort.x ||
-                _previousViewPort.y != _viewPort.y)
+            if (forceUpdate || !RectangleUtil.compare(_viewPort, _previousViewPort))
             {
                 _previousViewPort.setTo(_viewPort.x, _viewPort.y, _viewPort.width, _viewPort.height);
-                
+
                 // Constrained mode requires that the viewport is within the native stage bounds;
                 // thus, we use a clipped viewport when configuring the back buffer. (In baseline
                 // mode, that's not necessary, but it does not hurt either.)
-                
+
                 _clippedViewPort = _viewPort.intersection(
                     new Rectangle(0, 0, _nativeStage.stageWidth, _nativeStage.stageHeight));
-
-                if (!shareContext)
-                {
-                    var contentScaleFactor:Number =
-                            _supportHighResolutions ? _nativeStage.contentsScaleFactor : 1.0;
 
-                    _painter.configureBackBuffer(_clippedViewPort, contentScaleFactor,
-                        _antiAliasing, true);
-                }
+                var contentScaleFactor:Number =
+                        _supportHighResolutions ? _nativeStage.contentsScaleFactor : 1.0;
+
+                _painter.configureBackBuffer(_clippedViewPort, contentScaleFactor,
+                    _antiAliasing, true);
             }
         }
 

starling/src/starling/rendering/Painter.as

@@ -186,6 +186,10 @@ package starling.rendering
         /** Sets the viewport dimensions and other attributes of the rendering buffer.
          *  Starling will call this method internally, so most apps won't need to mess with this.
          *
+         *  <p>Beware: if <code>shareContext</code> is enabled, the method will only update the
+         *  painter's context-related information (like the size of the back buffer), but won't
+         *  make any actual changes to the context.</p>
+         *
          * @param viewPort                the position and size of the area that should be rendered
          *                                into, in pixels.
          * @param contentScaleFactor      only relevant for Desktop (!) HiDPI screens. If you want
@@ -200,28 +204,31 @@ package starling.rendering
         public function configureBackBuffer(viewPort:Rectangle, contentScaleFactor:Number,
                                             antiAlias:int, enableDepthAndStencil:Boolean):void
         {
-            enableDepthAndStencil &&= SystemUtil.supportsDepthAndStencil;
+            if (!_shareContext)
+            {
+                enableDepthAndStencil &&= SystemUtil.supportsDepthAndStencil;
 
-            // Changing the stage3D position might move the back buffer to invalid bounds
-            // temporarily. To avoid problems, we set it to the smallest possible size first.
+                // Changing the stage3D position might move the back buffer to invalid bounds
+                // temporarily. To avoid problems, we set it to the smallest possible size first.
 
-            if (_context.profile == "baselineConstrained")
-                _context.configureBackBuffer(32, 32, antiAlias, enableDepthAndStencil);
+                if (_context.profile == "baselineConstrained")
+                    _context.configureBackBuffer(32, 32, antiAlias, enableDepthAndStencil);
 
-            // If supporting HiDPI mode would exceed the maximum buffer size
-            // (can happen e.g in software mode), we stick to the low resolution.
+                // If supporting HiDPI mode would exceed the maximum buffer size
+                // (can happen e.g in software mode), we stick to the low resolution.
 
-            if (viewPort.width  * contentScaleFactor > _context.maxBackBufferWidth ||
-                viewPort.height * contentScaleFactor > _context.maxBackBufferHeight)
-            {
-                contentScaleFactor = 1.0;
-            }
+                if (viewPort.width  * contentScaleFactor > _context.maxBackBufferWidth ||
+                    viewPort.height * contentScaleFactor > _context.maxBackBufferHeight)
+                {
+                    contentScaleFactor = 1.0;
+                }
 
-            _stage3D.x = viewPort.x;
-            _stage3D.y = viewPort.y;
+                _stage3D.x = viewPort.x;
+                _stage3D.y = viewPort.y;
 
-            _context.configureBackBuffer(viewPort.width, viewPort.height,
+                _context.configureBackBuffer(viewPort.width, viewPort.height,
                     antiAlias, enableDepthAndStencil, contentScaleFactor != 1.0);
+            }
 
             _backBufferWidth  = viewPort.width;
             _backBufferHeight = viewPort.height;