Window and game area
The window of the game is the area in which the game is displayed. It DOES NOT refer to the system window that includes the toolbar, title bar on the top and a frame on the other three sides.
The "De/activate fullscreen" action allows you to toggle the game between fullscreen on/off. When the window is in fullscreen, it will take up as much area as possible. You can control the action using the "YES" and "NO" actions.
The margin of the window is the distance between the side of the window and the game window displayed. Shown below is the preview of a game with 100 px margins on all 4 sides.
Notice the black borders on all for sides of the window. The width of the borders is 100px.
Size of the window
Size of the window is the number of pixels visible in the game. The "Width" field refers to the number of pixels in the horizontal directions while the "Height" field refers to the number of pixels in the vertical direction.
While setting the size of the window, if you want to scale the current area to the set resolution, choose "NO". This will decrease the visual quality of the game if the size entered is lower than default and will increase the visual quality if the size entered is higher than the default size.
If you want to scale the set resolution to the window area, choose "YES". This will crop the window and display only the number of pixels entered in the action. This does not affect the visual quality as long as the game is scaled up or down because of the size of the system window.
The game is cropped starting from the top-left corner of the game.
The window title is the name of the window that is visible on the title bar (located at the top) of the window. The default title name is "Preview of ProjectName" during a preview.
By default, the game name is used for the executable name (on Windows, macOS and Linux), the app name (on Android and iOS) and the title bar (on Windows, macOS and Linux) (and the page title for HTML5 games). You can learn more about it in game properties.
With the action to change the title, the title bar on Windows, macOS and Linux will be changed. Nothing will be visible on Android and iOS. For HTML5 games, the web page title will be changed.
All actions, conditions and expressions are listed in the window reference page.