Handle Horizontal Scrolling in SDL

Handling horizontal scrolling in SDL is quite similar to handling vertical scrolling. Horizontal scroll events are detected through the SDL_MOUSEWHEEL event type and processed using the SDL_MouseWheelEvent structure.

The x member variable of SDL_MouseWheelEvent contains the amount of horizontal scroll. Here’s an example:

1#include <SDL.h>
2#include <iostream>
3
4int main(int argc, char* argv[]) {
5  SDL_Init(SDL_INIT_VIDEO);
6  SDL_Window* window = SDL_CreateWindow(
7    "Horizontal Scrolling Example",
8    SDL_WINDOWPOS_UNDEFINED,
9    SDL_WINDOWPOS_UNDEFINED,
10    800, 600,
11    SDL_WINDOW_SHOWN
12  );
13
14  SDL_Event event;
15  bool running = true;
16
17  while (running) {
18    while (SDL_PollEvent(&event)) {
19      if (event.type == SDL_MOUSEWHEEL) {
20        if (event.wheel.x != 0) {
21          std::cout << "Horizontal scroll detected: "
22                    << event.wheel.x << '\n'; 
23        }
24      }
25      if (event.type == SDL_QUIT) {
26        running = false;
27      }
28    }
29  }
30
31  SDL_DestroyWindow(window);
32  SDL_Quit();
33  return 0;
34}

1Horizontal scroll detected: -1
2Horizontal scroll detected: 1

To process the horizontal scroll events within the event loop, you can check if the x member of event.wheel is non-zero.

This indicates a horizontal scroll action. Positive values represent scrolling to the right, and negative values represent scrolling to the left.

Based on your application’s needs, you can implement custom handling logic for horizontal scrolling. For example, you might want to pan a view or navigate through a list.

Here is an example function to handle both vertical and horizontal scrolling:

1void HandleMouseWheel(
2  const SDL_MouseWheelEvent& wheel) {
3  if (wheel.y != 0) {
4    std::cout << "Vertical scroll detected: "
5      << wheel.y << '\n';  
6  }
7  if (wheel.x != 0) {
8    std::cout << "Horizontal scroll detected: "
9      << wheel.x << '\n';  
10  }
11}

In your main loop, you would call this function when SDL_MOUSEWHEEL events are detected:

1while (running) {
2  while (SDL_PollEvent(&event)) {
3    if (event.type == SDL_MOUSEWHEEL) {
4      HandleMouseWheel(event.wheel);
5    }
6    if (event.type == SDL_QUIT) {
7      running = false;
8    }
9  }
10}

By following these steps, you can effectively handle horizontal scrolling events in SDL. This allows you to create more responsive and interactive applications that can respond to various input methods from users.