How can I save the player's preferred fullscreen mode and restore it the next time they launch the game?

Question

Ryan McCombe · Accepted Answer

Saving and restoring player preferences is an essential feature for any game. Here's how to implement a robust system for handling fullscreen preferences:

Basic Implementation

Here's a basic framework that we can use to save and load display preferences:

1#include <SDL.h>
2#include <fstream>
3#include <iostream>
4
5struct DisplayPreferences {
6  enum class Mode {
7    Windowed,
8    DesktopFullscreen,
9    ExclusiveFullscreen
10  };
11
12  Mode FullscreenMode{Mode::Windowed};
13  int WindowWidth{1920};
14  int WindowHeight{1080};
15  int DisplayIndex{0};
16};
17
18void SavePreferences(
19  const DisplayPreferences& Prefs) {
20  std::ofstream File{
21    "display_prefs.dat", std::ios::binary};
22  File.write(
23    reinterpret_cast<const char*>(&Prefs),
24    sizeof(DisplayPreferences));
25}
26
27DisplayPreferences LoadPreferences() {
28  DisplayPreferences Prefs;
29  std::ifstream File{
30    "display_prefs.dat", std::ios::binary};
31
32  if (File) {
33    File.read(reinterpret_cast<char*>(&Prefs),
34              sizeof(DisplayPreferences));
35  }
36
37  return Prefs;
38}
39
40void ApplyPreferences(
41  SDL_Window* Window,
42  const DisplayPreferences& Prefs
43) {
44  // First set window size
45  SDL_SetWindowSize(
46    Window,
47    Prefs.WindowWidth,
48    Prefs.WindowHeight);
49
50  // Then apply fullscreen mode
51  switch (Prefs.FullscreenMode) {
52  case DisplayPreferences::Mode::Windowed:
53    SDL_SetWindowFullscreen(Window, 0);
54    break;
55  case
56  DisplayPreferences::Mode::DesktopFullscreen:
57    SDL_SetWindowFullscreen(
58      Window, SDL_WINDOW_FULLSCREEN_DESKTOP);
59    break;
60  case
61  DisplayPreferences::Mode::ExclusiveFullscreen:
62    SDL_SetWindowFullscreen(
63      Window, SDL_WINDOW_FULLSCREEN);
64    break;
65  }
66}

Using JSON for Better Flexibility

For a more maintainable solution, consider using JSON to store preferences:

1#include <SDL.h>
2#include <fstream>
3#include <nlohmann/json.hpp>
4
5void SavePreferencesJson(
6  const DisplayPreferences& Prefs
7) {
8  nlohmann::json Json;
9  Json["fullscreen_mode"] =
10    static_cast<int>(Prefs.FullscreenMode);
11  Json["window_width"] =
12    Prefs.WindowWidth;
13  Json["window_height"] =
14    Prefs.WindowHeight;
15  Json["display_index"] =
16    Prefs.DisplayIndex;
17
18  std::ofstream File{"display_prefs.json"};
19  
20  // Pretty print with 2 space indent
21  File << Json.dump(2);
22}

The JSON approach makes the preferences file human-readable and easier to modify or debug. However, you'll need to include a JSON library in your project. We cover the popular nlohmann::json library here:

Using JSON in Modern C++

A practical guide to working with the JSON data format in C++ using the popular nlohmann::json library.

View Related Lesson

Fullscreen Windows

Saving Display Preferences

Basic Implementation

Using JSON for Better Flexibility

Using JSON in Modern C++

Fullscreen Windows

Game Development with SDL2

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