SDL Mouse Motion Events

SDL_MOUSEMOTION and SDL_MouseMotionEvent are both related to mouse movement in SDL, but they serve different purposes in the event handling system.

SDL_MOUSEMOTION

SDL_MOUSEMOTION is an event type constant used to identify mouse motion events. When the mouse is moved, SDL generates an event with this type.

You check for this event type in your event loop to determine if the user has moved the mouse.

Here’s an example of how to use SDL_MOUSEMOTION in an event loop:

1SDL_Event event;
2while (SDL_PollEvent(&event)) {
3  if (event.type == SDL_MOUSEMOTION) {
4    std::cout << "Mouse moved to - x: "
5      << event.motion.x << ", y: "
6      << event.motion.y << '\n';  
7  }
8}

SDL_MouseMotionEvent

SDL_MouseMotionEvent is a structure that contains detailed information about a mouse motion event.

When SDL_PollEvent() updates the SDL_Event structure with a mouse motion event, the motion member of the SDL_Event structure is an SDL_MouseMotionEvent.

Here’s an example structure:

1typedef struct SDL_MouseMotionEvent {
2  Uint32 type;      // Event type, SDL_MOUSEMOTION
3  Uint32 timestamp; // Timestamp of the event
4  Uint32 windowID;  // The window with mouse focus
5  Uint32 which;     // The mouse instance ID
6  Uint32 state;     // The current button state
7  Sint32 x;         // X coordinate of the mouse
8  Sint32 y;         // Y coordinate of the mouse
9  Sint32 xrel;      // Relative motion in the X direction
10  Sint32 yrel;      // Relative motion in the Y direction
11} SDL_MouseMotionEvent;

Differences and Usage

• Event Type: SDL_MOUSEMOTION is an event type constant, while SDL_MouseMotionEvent is a structure containing detailed information about the mouse motion event.
• Detection: Use SDL_MOUSEMOTION to detect a mouse motion event in the event loop. Once detected, you can access the motion member of the SDL_Event structure to get details.
• Details: SDL_MouseMotionEvent provides detailed information such as the cursor's new position (x, y), relative movement (xrel, yrel), and the state of mouse buttons during the movement.

Here’s a full example demonstrating how to use both:

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 Motion",
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        SDL_MouseMotionEvent& motion = event.motion;
32
33        std::cout << "Mouse moved to - x: "
34          << motion.x << ", y: " << motion.y << '\n';  
35
36        std::cout << "Relative movement - xrel: "
37          << motion.xrel << ", yrel: "
38          << motion.yrel << '\n';  
39      }
40    }
41  }
42
43  SDL_DestroyWindow(window);
44  SDL_Quit();
45  
46  return 0;
47}

1Mouse moved to - x: 150, y: 200
2Relative movement - xrel: 5, yrel: 5

In summary, use SDL_MOUSEMOTION to detect mouse movement events and SDL_MouseMotionEvent to access detailed information about the motion.