Handling Different Screen Resolutions in SDL2

Handling different screen resolutions is crucial for creating a game that looks good on various devices. Here's a strategy you can use:

Define a Base Resolution

First, decide on a base resolution for your game. This is the resolution you'll use for designing your game's layout and assets. For example, let's say we choose 1280x720 as our base resolution.

Calculate a Scaling Factor

When your game starts, calculate a scaling factor based on the actual screen resolution:

1#include <SDL.h>
2#include <iostream>
3
4int main() {
5  SDL_Init(SDL_INIT_VIDEO);
6
7  SDL_DisplayMode dm;
8  if (SDL_GetCurrentDisplayMode(0, &dm) != 0) {
9    std::cout <<
10      "SDL_GetCurrentDisplayMode failed: " <<
11      SDL_GetError() << "\n";
12    return 1;
13  }
14
15  const int BASE_WIDTH = 1280;
16  const int BASE_HEIGHT = 720;
17  float scaleX = dm.w / static_cast<float>(
18    BASE_WIDTH);
19  float scaleY = dm.h / static_cast<float>(
20    BASE_HEIGHT);
21  float scale = std::min(scaleX, scaleY);
22
23  std::cout << "Screen resolution: " << dm.w <<
24    "x" << dm.h << "\n";
25  std::cout << "Scaling factor: " << scale <<
26    "\n";
27
28  SDL_Quit();
29  return 0;
30}

Apply the Scaling Factor

Use this scaling factor when rendering your game elements. You can create a utility function to scale positions and sizes:

1SDL_Rect ScaleRect(const SDL_Rect& rect,
2                   float scale) {
3  return SDL_Rect{
4    static_cast<int>(rect.x * scale),
5    static_cast<int>(rect.y * scale),
6    static_cast<int>(rect.w * scale),
7    static_cast<int>(rect.h * scale)};
8}

Render at Native Resolution

Create your SDL window at the native screen resolution, but render your game elements using the scaled positions and sizes:

1SDL_Window* window =
2  SDL_CreateWindow("Game",
3                   SDL_WINDOWPOS_UNDEFINED,
4                   SDL_WINDOWPOS_UNDEFINED,
5                   dm.w, dm.h,
6                   SDL_WINDOW_FULLSCREEN);
7
8// In your render loop:
9SDL_Rect baseRect{100, 100, 200, 200};
10SDL_Rect scaledRect =
11  ScaleRect(baseRect, scale);
12SDL_RenderFillRect(renderer, &scaledRect);

By following this approach, your game will maintain its relative layout across different screen resolutions while taking advantage of the full screen real estate available.