@Watercolor_Games It's not a PictureBox. It's a custom GraphicsDeviceControl, which inherits from a regular System.Windows.Forms.Control. The contents of the back buffer is presented though a 'SwapChainRenderTarget', which just inherits from RenderTarget2D. So it's also possible to have different render targets and work with complex Effects / shaders.
You can treat MonoGame.Forms basically the same you would do with your MonoGame game, but so far I didn't work out a control-resize-solution regarding to the drawn content on the SwapChainRenderTarget. In the moment there are also other limitations (see below).
@SNaidamast Thanks :] MonoGame.Forms is build with in mind of having a simple solution of integrating a MonoGame render window / control to a WindowsForms project to create you own editor environment. Theoretically you could host a game into a form now, yes, but there are some things currently missing in MonoGame.Forms. For example: GamePad and Keyboard controls. When I have time in the future I could imagine to implement keyboard funtionallity, where the key presses are recognised. In the moment you have only the option to use the left, right and middle mouse button.
You asked if it's possible to use windows forms controls (UI) in relation to game mechanics. The answer is yes of course! It's already in the sample project. Just take a look. This is a key feature, because it should be possible to create a complex editor environment, which has this Forms-Control-MonoGame-Mechanics-relation . But you couldn't use your MonoGame game with a reference to MonoGame.Forms to create your ingame UI. You rather would host you game inside a forms project to use the forms controls capabilities. But as I sad you would have some limitations.
Regarding ratio scaling: I didn't try this so far, because I didn't need this feature in the past. But this project is open source, so it's possible for everyone to work on that an then share it with a nice PR
I'm generally open for good ideas, which enhance this project; thanks at all for you nice input so far!