Mouse State

Calculating Mouse Speed

Can I get the mouse speed or how fast it's moving?

Abstract art representing computer programming

Yes! To calculate mouse speed, you'll need to track both the current and previous positions of the mouse, then calculate the distance moved over time. Here's one way to do it:

1#include <SDL.h>
2#include <cmath>
3#include <iostream>
4#include "Window.h"
5
6class MouseTracker {
7 public:
8  void Tick() {
9    // Get current mouse position
10    int CurrentX, CurrentY;
11    SDL_GetMouseState(&CurrentX, &CurrentY);
12
13    // Get current time in milliseconds
14    Uint32 CurrentTime = SDL_GetTicks();
15
16    // Calculate time difference
17    float DeltaTime = (CurrentTime - LastTime)
18      / 1000.0f;  
19
20    // Calculate distance moved
21    float DX = CurrentX - LastX;
22    float DY = CurrentY - LastY;
23    float Distance = std::sqrt(
24      DX * DX + DY * DY);
25
26    // Calculate speed (pixels per second)
27    float Speed = Distance / DeltaTime;  
28
29    if (Distance > 0) {
30      std::cout << "Mouse speed: "
31        << Speed << " pixels/second\n";
32    }
33
34    // Store current values for next frame
35    LastX = CurrentX;
36    LastY = CurrentY;
37    LastTime = CurrentTime;
38  }
39
40 private:
41  int LastX{0};
42  int LastY{0};
43  Uint32 LastTime{SDL_GetTicks()};
44};
45
46int main(int argc, char** argv) {
47  SDL_Init(SDL_INIT_VIDEO);
48  Window GameWindow;
49  MouseTracker Tracker;
50  SDL_Event E;
51
52  while (true) {
53    while (SDL_PollEvent(&E)) {
54      // Handle other events...
55    }
56
57    Tracker.Tick();
58    GameWindow.Update();
59  }
60
61  SDL_Quit();
62  return 0;
63}

1Mouse speed: 245.8 pixels/second
2Mouse speed: 312.3 pixels/second
3Mouse speed: 178.9 pixels/second

How It Works

The speed calculation involves three main steps:

Track position changes by storing the last known position and comparing it with the current position
Measure time between updates using SDL_GetTicks()
Calculate speed using the formula: speed = distance / time

The distance is calculated using the Pythagorean theorem $\sqrt{dx^2 + dy^2}$ to get the actual distance moved, even when moving diagonally.

You might want to smooth out the speed values using a moving average if you need more stable readings, as raw mouse movement can be quite jittery. You could also calculate separate X and Y speeds if you need directional velocity information.

Remember that this gives you speed in pixels per second. If you need the speed in a different unit (like game units), you'll need to convert the pixel distances accordingly.

This Question is from the Lesson: