Decorations in fullscreen modes

In fullscreen modes, window decorations are typically irrelevant because the window is either resized to match the screen resolution (exclusive fullscreen) or displayed borderless on top of other windows (fullscreen desktop).

SDL2 provides two fullscreen modes:

1. Exclusive Fullscreen (SDL_WINDOW_FULLSCREEN): The window occupies the entire screen resolution, and all decorations are removed.
2. Fullscreen Desktop (SDL_WINDOW_FULLSCREEN_DESKTOP): The window behaves as a borderless window but matches the desktop resolution.

Example of switching between fullscreen modes:

1#include <SDL.h>
2
3int main() {
4  SDL_Init(SDL_INIT_VIDEO);
5
6  SDL_Window* Window{SDL_CreateWindow(
7    "Fullscreen Demo",
8    SDL_WINDOWPOS_CENTERED,
9    SDL_WINDOWPOS_CENTERED,
10    800, 600,
11    SDL_WINDOW_SHOWN 
12  )};
13
14  SDL_SetWindowFullscreen(
15    Window, SDL_WINDOW_FULLSCREEN_DESKTOP); 
16  
17  // Display fullscreen for 3 seconds
18  SDL_Delay(3000);
19  
20  // Restore windowed mode
21  SDL_SetWindowFullscreen(Window, 0); 
22  SDL_Delay(3000);
23
24  SDL_DestroyWindow(Window);
25  SDL_Quit();
26}

1Displays fullscreen desktop mode, then returns to windowed mode.

In fullscreen desktop mode, decorations are completely absent, and the window is effectively borderless. Exclusive fullscreen mode always removes decorations because it takes complete control of the display.