如何应用alpha蒙版或剪贴蒙版，使除矩形以外的所有内容都变得模糊？我照常做:GraphicsEffect->EffectFactory->Brush->SettoSpriteVisualvargraphicsEffect=newBlendEffect{Mode=BlendEffectMode.Multiply,Background=newColorSourceEffect{Name="Tint",Color=Windows.UI.Color.FromArgb(50,0,255,0),},Foreground=newGaussianBlurEffect(){Name="Blur",So