Option to retain aspect ratio in free scale output and fullscreen

[pinntokuru]

Choosing Output->Scale->Free lets the user resize the clone window however they want, but the game window also gets stretched or squashed in the process. This means the feature is hard to use as any manual resizing disturbs the aspect ratio. Fullscreen in ultrawide monitors ends up being stretched as well.

Would like to have an option to resize the window/go fullscreen while retaining aspect ratio by dynamically adding black bars above or to the sides of the game display.

[ParanormalBanana]

I need this as well. I was trying to play a RPGMaker Ace game, and ShaderGlass is the solution to add filters to those games, but using fullscreen mode is incompatible with shaderglass, and borderless is impossible. So the idea is to leave it windowed and pixel perfect, and use ShaderGlass to go fullscreen with the desired shaders. Would be perfect except it isn't because as soon as you go "free scale" Shaderglass stops caring about aspect ratio, even if I try to set one in the dedicated menu.

This would be awesome :)