Display, viewport and screen resolution
Brief explanation of the differences between display viewport, viewport and screen resolution. This could be useful when you want to resize your game for different screens.
Settings display viewport
It's the base resolution for your project, the one defined in the "project settings" (scene > settings > display), and since it's a fixed value, it's the one you need to focus when creating assets and resizing elements.
Globals.get("display")
Viewport
The actual viewport size relative to the viewport defined in the settings, It's managed by the engine depending on the strecth_mode, strecth_aspect settings and the screen resolution.
As an example if you are using some stretch_mode and strecth_aspect = keep_width, the width of the viewport will be always the width value defined in the settings no matter if the actual window or screen is bigger or smaller than that value.
get_viewport_rect().size
Screen and window resolution
The screen or window resolution of the device you are running on.
OS.get_screen_size() OS.get_window_size()
In mobile we can consider that the screen and window resolution will be equal since in most cases the engine will go fullscreen.