When to use PresentationParameters.BackBufferWidth vs .Viewport.Width
Had to shorten the calls to make the question more readable but... When is correct or incorrect to use on or the other ? I guess in most cases is the same as you just have the one Viewport but if going split screen I guess you ll have more
Usually you want the viewport size, as this is the region within which rendering actually takes place. If you ever add anything like split-screen or picture-in-picture rendering, then you must use the viewport. So you may as well use it to begin with. You should use the backbuffer size only when that is what you actually want. For example, you want the backbuffer when taking screenshots, or setting viewport positions. I've got a more detailed answer to a very similar question over on the game dev site.
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