do not calc renderView.contentScaleFactor when MTIImageView is not in an on-screen window
do not calc renderView.contentScaleFactor when MTIImageView is not in an on-screen window

MetalPetal/MetalPetal,MetalPetal/MetalPetal,MetalPetal/MetalPetal,MetalPetal/MetalPetal,MetalPetal/MetalPetal