C4d: Constrain viewport to film aspect ratio

When working with Maxon Cinema 4d, many times I adjust the size of the viewport (even while using Layouts). I would love to have a checkbox in eacht viewport to Constrain Viewport to Film Aspect Ratio, defined by Width and Height in Render Settings. So when your render settings are 16:9, checked viewports are 16:9, no matter what happens.