Store Mouse Motion Events

Storing and transferring mouse motion events in SDL can be useful for handling complex input scenarios.

You can achieve this by using the SDL_MouseMotionEvent structure to capture the details of the event and then store it in a suitable data structure for later use.

Capturing Mouse Motion Events

First, you need to capture the mouse motion events in your event loop. The SDL_MOUSEMOTION event provides the details of the mouse motion in the motion member of the SDL_Event structure.

Example Code

Here’s an example demonstrating how to capture, store, and later use mouse motion events:

1#include <SDL.h>
2#include <iostream>
3#include <vector>
4
5struct MouseMotion {
6  int x;
7  int y;
8  int xrel;
9  int yrel;
10};
11
12void HandleMouseMotion(
13  const SDL_MouseMotionEvent& motionEvent,
14  std::vector<MouseMotion>& motions
15) {
16  MouseMotion motion{
17    motionEvent.x, motionEvent.y,
18    motionEvent.xrel, motionEvent.yrel
19  };
20  motions.push_back(motion);
21}
22
23void ProcessStoredMotions(
24  const std::vector<MouseMotion>& motions) {
25  for (const auto& motion : motions) {
26    std::cout << "Stored motion "
27      << "- x: " << motion.x
28      << ", y: " << motion.y
29      << ", xrel: " << motion.xrel
30      << ", yrel: " << motion.yrel << '\n';
31  }
32}
33
34int main(int argc, char* argv[]) {
35  if (SDL_Init(SDL_INIT_VIDEO) != 0) {
36    std::cerr << "SDL_Init Error: "
37      << SDL_GetError() << '\n';
38    return 1;
39  }
40
41  SDL_Window* window = SDL_CreateWindow(
42    "Store Mouse Motion Events",
43    100, 100, 640, 480,
44    SDL_WINDOW_SHOWN
45  );
46
47  if (window == nullptr) {
48    std::cerr << "SDL_CreateWindow Error: "
49      << SDL_GetError() << '\n';
50    SDL_Quit();
51    return 1;
52  }
53
54  SDL_Event event;
55  std::vector<MouseMotion> mouseMotions;
56  bool running = true;
57  while (running) {
58    while (SDL_PollEvent(&event)) {
59      if (event.type == SDL_QUIT) {
60        running = false;
61      } else if (event.type == SDL_MOUSEMOTION) {
62        HandleMouseMotion(
63          event.motion, mouseMotions);
64      }
65    }
66  }
67
68  ProcessStoredMotions(mouseMotions);
69
70  SDL_DestroyWindow(window);
71  SDL_Quit();
72  return 0;
73}

1Stored motion - x: 150, y: 200, xrel: 5, yrel: 5
2Stored motion - x: 155, y: 205, xrel: 5, yrel: 5

Explanation

• Initialization: SDL is initialized, and a window is created.
• Event Loop: The event loop captures SDL_MOUSEMOTION events and calls the HandleMouseMotion() function to store the event details.
• Storage: The MouseMotion structure is used to store the relevant details of the motion event (x, y, xrel, yrel). These structures are stored in a std::vector.
• Processing Stored Events: After exiting the event loop, the stored mouse motion events are processed in the ProcessStoredMotions() function.

Advantages

• Organized Storage: Using a std::vector allows for easy storage and retrieval of mouse motion events.
• Flexibility: You can process stored events at a later time, making it easier to handle complex input scenarios.
• Detailed Information: Storing the x, y, xrel, and yrel values provides comprehensive details about each motion event.

Summary

Storing and transferring mouse motion events in SDL involves capturing the events in the event loop, storing the details in a suitable data structure like std::vector, and processing them as needed.

This approach is useful for scenarios where you need to handle mouse input more flexibly and in an organized manner.