Retrieve Mouse Position

To retrieve the current position of the mouse cursor in SDL, you need to handle SDL_MOUSEMOTION events.

When the user moves the mouse, SDL generates an event of type SDL_MOUSEMOTION. This event contains the new x and y coordinates of the mouse cursor. You can access these coordinates using the motion member of the SDL_Event structure.

Here’s a basic example of how to retrieve and print the mouse position:

1#include <SDL.h>
2#include <iostream>
3
4int main(int argc, char* argv[]) {
5  if (SDL_Init(SDL_INIT_VIDEO) != 0) {
6    std::cerr << "SDL_Init Error: "
7      << SDL_GetError() << '\n';
8    return 1;
9  }
10
11  SDL_Window* window = SDL_CreateWindow(
12    "Mouse Position",
13    100, 100, 640, 480,
14    SDL_WINDOW_SHOWN
15  );
16
17  if (window == nullptr) {
18    std::cerr << "SDL_CreateWindow Error: "
19      << SDL_GetError() << '\n';
20    SDL_Quit();
21    return 1;
22  }
23
24  SDL_Event event;
25  bool running = true;
26  while (running) {
27    while (SDL_PollEvent(&event)) {
28      if (event.type == SDL_QUIT) {
29        running = false;
30      } else if (event.type == SDL_MOUSEMOTION) {
31        int x = event.motion.x;
32        int y = event.motion.y;
33        std::cout << "Mouse Position - x: "
34          << x << ", y: " << y << '\n'; 
35      }
36    }
37  }
38
39  SDL_DestroyWindow(window);
40  SDL_Quit();
41  
42  return 0;
43}

1Mouse Position - x: 123, y: 456
2Mouse Position - x: 130, y: 460
3Mouse Position - x: 140, y: 470

In this example:

• SDL_Init(SDL_INIT_VIDEO) initializes the SDL video subsystem.
• SDL_CreateWindow() creates a window where the mouse events will be captured.
• The SDL_PollEvent() function polls for currently pending events. If an event is detected, it updates the event object.
• Inside the event loop, we check if the event type is SDL_MOUSEMOTION and then retrieve the mouse coordinates from event.motion.x and event.motion.y.

These coordinates are relative to the window's top-left corner.

If you need the mouse position relative to the screen, you can use SDL_GetMouseState() instead, which returns the current state of the mouse and fills the provided x and y pointers with the mouse cursor’s screen coordinates.

Here’s an example using SDL_GetMouseState():

1int x, y;
2SDL_GetMouseState(&x, &y);
3std::cout << "Mouse Position - x: " << x
4          << ", y: " << y << '\n';

This code retrieves the current mouse position relative to the entire screen, not just the window. Using these methods, you can accurately track and use the mouse position in your SDL applications.