BACKENDS: SDL - GMM and game resolution doesn't scale together for enhanced graphics on small screens

[dafioram]

If the player selects a graphics mode that is larger than their screen resolution then the game resolution won't scale, but the GMM will which leads to the GMM shrinking relative to the game.

Before PR1007 the game screen would also enlarge so the GMM and game scaled together. It also makes the GMM letters not very sharp, but can be improved by turning on Filter graphics.

This is easy to reproduce in a VM.

1. Start up VM and make it have a small resolution (window it).
2. Start up scummvm and set it to HQ3x to maximize game resolution.
3. Start a game and hit ctrl+f5 and you should see a small GMM.

I guess if the scaling isn't possible the GMM should probably revert to the lower resolution.

[csnover]

I’m not sure what magic is needed to get the GUI to render using the device resolution in the SurfaceSdl renderer as it does with the OpenGL renderer, but that would be the preferred solution for this problem since then you’re guaranteed that the overlay will fit and be sharp. Since there is already code to make the GUI work correctly in OpenGL, I assume/hope this is just a matter of doing the research to see what that renderer is doing and then duplicate it in SurfaceSdl (and by “duplicate”, I mean make it common code in WindowedGraphicsManager :)).