What happens if a player has a monitor with a different aspect ratio than our game's resolution?

Question

Ryan McCombe · Accepted Answer

When your game's aspect ratio doesn't match the monitor's, SDL handles it by either adding black bars (letterboxing/pillarboxing) or stretching the content. Here's how different scenarios are handled.

Desktop Fullscreen

In desktop fullscreen mode, SDL maintains your game's aspect ratio by default. If your game renders at 1920x1080 (16:9) but the monitor is 2560x1440 (16:9), SDL scales the content proportionally. However, if the monitor is 1920x1200 (16:10), SDL adds black bars at the top and bottom.

Here's how to detect the display's aspect ratio:

1#include <SDL.h>
2#include <iostream>
3
4void CheckAspectRatio(SDL_Window* Window) {
5  // Get display bounds
6  SDL_Rect DisplayBounds;
7  int DisplayIndex{
8    SDL_GetWindowDisplayIndex(Window)};
9  SDL_GetDisplayBounds(DisplayIndex,
10                       &DisplayBounds);
11
12  // Calculate aspect ratios
13  float DisplayRatio{
14    static_cast<float>(DisplayBounds.w) /
15      DisplayBounds.h
16  };
17
18  int GameWidth, GameHeight;
19  SDL_GetWindowSize(Window, &GameWidth,
20                    &GameHeight);
21  float GameRatio{
22    static_cast<float>(GameWidth) / GameHeight};
23
24  std::cout << "Display ratio: " << DisplayRatio
25    << "\nGame ratio: " << GameRatio << "\n";
26
27  if (DisplayRatio > GameRatio) {
28    std::cout <<
29      "Black bars will appear on the sides\n";
30  } else if (DisplayRatio < GameRatio) {
31    std::cout <<
32      "Black bars will appear on top/bottom\n";
33  }
34}

Exclusive Fullscreen

In exclusive fullscreen, the monitor changes its resolution to match your game. However, if the aspect ratios don't match, you'll need to decide how to handle it:

1#include <SDL.h>
2
3void ConfigureAspectRatio(SDL_Window* Window,
4                          bool PreserveRatio) {
5  if (PreserveRatio) {
6    // Add letterboxing/pillarboxing
7    SDL_RenderSetLogicalSize(
8      SDL_GetRenderer(Window), 1920, 1080);
9  } else {
10    // Stretch to fill
11    SDL_RenderSetScale(SDL_GetRenderer(Window),
12                       1.0f, 1.0f); 
13  }
14}

Most games provide options for how to handle aspect ratio differences, letting players choose between preserving the aspect ratio with black bars or stretching to fill the screen.

Fullscreen Windows

Managing Different Aspect Ratios

Desktop Fullscreen

Exclusive Fullscreen

Fullscreen Windows

Game Development with SDL2

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