Fullscreen scaling

I have set window size in project properties to 1680x945 (yes that size is intentional!) and full screen is set to Scaled.

Previews run in fullscreen mode at a 1680x1050 resolution. According to the manual I should be seeing isotropic scaling with parts of the screen being blank (since project window height is ca. 100 pixels too small).

scirra.com/tutorials/73/supporting-multiple-screen-sizes/page-1

However, I am using a SpaceBlaster like vertical layout that's much larger than 1680x945 and when previewing the game Construct2 actually fills the entire screen- there is no black border. Is that intended behavior?

In case this was too confusing. Try this:

open SpaceBlaster, set Project Properties to Full Screen: on (scaled) and window size to your screen width but make the height only half your screen height, e.g. 1280x500. Change the game layout to your screen width, and make the background tiles wider as well. Run game. It's now filling the entire screen despite the weird window size we picked.

Fullscreen scaling never adds black bars - where on the tutorial did you think it said that? It's on our todo list to add a 'barred' fullscreen scaling mode.

Based on this:

caling mode zooms according to the aspect ratio. If your window size is square and you resize the window to a rectangle, the game will scale to fit a square in the middle of the window, with extra space at the sides.

If my window aspect ratio is set to 2:1 I would expect it to remain 2:1 with "extra space at the sides". That's not the behavior I am seeing though.

Ah, extra space at the sides means more of your layout showing, not black bars... I'll edit the tutorial to clarify.

What's the point of using scale mode then? In this case scale and crop mode yield identical results- a player with a larger screen will see more of the playfield (leading to an unfair advantage).

Scale mode adjusts the layout zoom whereas crop mode doesn't. Scale mode only shows more of the layout if the aspect ratio of the window changes, whereas crop mode always shows more if the window is bigger.

The feature is designed for mobiles and tablets with different sized screens with roughly the same aspect ratios (no extremities anyway, like you can get by resizing a browser window to weird shapes). You could try adding your own black bars with some black Tiled Background objects on the top layer.

I'm looking forward to the black bar fullscreen scale too.

You can do the black bars yourself with events. Probably a lot more flexible than as a project setting.