SDL: Get Mouse Screen Coordinates

Yes, SDL provides functions to get the mouse cursor's position relative to the global screen/desktop coordinates, rather than just relative to a specific application window.

Using SDL_GetGlobalMouseState()

The primary function for this is SDL_GetGlobalMouseState(). It retrieves the current state of the mouse, including its position on the screen.

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 could not initialize! SDL_Error: "
7      << SDL_GetError() << '\n';
8    return 1;
9  }
10
11  // No window creation needed just to get global state
12
13  int mouseX, mouseY;
14  Uint32 mouseButtonState = SDL_GetGlobalMouseState(
15    &mouseX, &mouseY                        
16  );                                        
17
18  std::cout << "Global Mouse Position - x: " << mouseX
19            << ", y: " << mouseY << '\n';
20
21  if (mouseButtonState & SDL_BUTTON(SDL_BUTTON_LEFT)) {
22    std::cout << "Left mouse button is pressed globally.\n";
23  }
24
25  SDL_Quit();
26  return 0;
27}

1Global Mouse Position - x: 1024, y: 512
2Left mouse button is pressed globally.

This function takes pointers to two integers (int* x, int* y) which it fills with the current global x and y coordinates of the mouse cursor. It also returns a bitmask representing the state of the mouse buttons globally (useful if you need to know button states without relying on window focus).

SDL_GetMouseState() (Relative to Focused Window)

For comparison, remember that SDL_GetMouseState() provides the mouse position relative to the window that currently has mouse focus. If no window in your application has focus, the coordinates returned by SDL_GetMouseState() might not be meaningful or could be relative to the desktop.

1// Inside your main loop or where you have a window context
2int windowMouseX, windowMouseY;
3SDL_GetMouseState(&windowMouseX, &windowMouseY);
4// windowMouseX, windowMouseY are relative to the focused window

When to Use Global Coordinates?

Getting global coordinates is less common in game development than window-relative coordinates, but it can be useful for:

• Applications that interact with the entire desktop (e.g., screen capture tools).
• Positioning new windows based on the current mouse position.
• Debugging purposes.

For most in-game interactions (clicking buttons, selecting units, aiming), you'll typically use the window-relative coordinates provided by mouse events (event.motion.x, event.button.x) or SDL_GetMouseState().