What is the point of a borderless fullscreen window?

Question

Quite a lot of game allow user to play in a "borderless fullscreen window" instead of a "fullscreen mode". I've been wondering. Why would one prefer a fullscreen window over the "built-in" fullscreen mode?

Simple test of my own showed me, that using fullscreen mode instead yields better performance. I also tried to search on Google and on SO, but most answers are gaming related or on how to actually create those windows in API X,Y or Z.

So what is the point of having a borderless fullscreen window? Are there any technical reasons?

Answer 1

"Regular" fullscreen involves taking "exclusive" access of the GPU, which means a lot more work in handling resolution switching, resource management (in older APIs, in particular) and so on, especially around supporting correct alt-tab behavior. This might seem odd at first, but it arises because when you lose exclusivity (when alt-tabbed out), your game's GPU resources are effectively evicted and must be restored when you tab back in.

A "borderless fullscreen" window is just a regular window, with window chrome disabled, that is the size of the whole screen. This means it acts just like a regular window and doesn't incur the extra complication and overhead of exclusive GPU access, which makes things easier for developers at the cost of some negligible performance. This is the main technical reason: less work.

It also makes things easier on users, usually, because many games that use exclusive fullscreen modes also happen to not handle alt-tab very well, and crash, or act oddly when restored to fullscreen. This can be exceedingly annoying for players who want to alt-tab to look at GameFAQs, chat on Discord or IRC, or whatever. It's also more friendly to multi-monitor setups.

Answer 2

In addition to Josh Petries very thorough answer, I would like to add a more practical upside of borderless fullscreen.

Having a setup with multiple monitors makes regular fullscreen a bit of a pain. Because changing focus to another window takes longer and causes the fullscreen application to minimize.

With borderless fullscreen on the other hand, the window in question is a regular window. This means, it can be in the background. Still visible while other windows overlap. With multiple monitors, it allows streamers for example to interact with their viewers while still focusing on the game.

Answer 3

Things for which borderless fullscreen windows are useful

• Double screen setups;

• Recording games (LPers, tutorials); A lot of content creators use software that allows for window capture, so capturing just the game window. This allows the creator to switch context to other programs without the risk of revealing sensitive information. If the game is exclusive fullscreen, capture software would have to capture the entire monitor, forcing the creator to either edit out context switches from the final video or to turn his screen black when livestreaming.;

• Multitasking;

• Avoiding bugs in the fullscreen implementation (wrong resolution, cut off edges, no mouse, infinite cycle of focus/defocus etc.);

• Sometimes performance; although real fullscreen should run faster, sometimes it has the exact inverse effect;

• Many games bug out when Alt-Tabbed (no sound, buggy graphics, long Alt-Tab reaction time which is annoying, cannot run anymore after trying to Alt-Tab back into the game, some block Alt-Tab altogether to the annoyance of the player);

• Often real full screen is reserving more space than necessary on smaller monitors, e.g. on 1370 it still reserves 1980 pixel width, so any other fullscreen window on the other screen is offset by 600 pixels to the right;

• Switching mouse between screens is a pain in the arse with fullscreen mode as well, wanna switch your music playlist? Takes 1 minute because of Alt-Tab loading times and slow reaction, not only does it take 15 seconds until you're out of the game, but getting in again takes longer and sometimes even bugs out in normally functional games.

• On low end computers your game might not be able to run smoothly in full screen mode but, when making the window smaller, the performance often improves as well. (Some content creators use this to capture downscaled games and upscale the video.)