Implement Inertia Scrolling in SDL

1#include <SDL.h>
2#include <iostream>
3#include <chrono>
4
5const float inertia = 0.999f;
6const float coefficient = 100.0f;
7
8float scrollPosition = 0.0f;
9float scrollVelocity = 0.0f;
10
11void HandleMouseWheel(SDL_MouseWheelEvent& wheel) {
12  scrollVelocity += wheel.y * coefficient; 
13}
14
15int main(int argc, char* argv[]) {
16  using namespace std::chrono;
17  SDL_Init(SDL_INIT_VIDEO);
18  SDL_Window* window = SDL_CreateWindow(
19    "Inertia Scrolling Example", 
20    SDL_WINDOWPOS_UNDEFINED, 
21    SDL_WINDOWPOS_UNDEFINED, 
22    800, 600, 
23    SDL_WINDOW_SHOWN
24  );
25  SDL_Renderer* renderer =
26    SDL_CreateRenderer(window, -1, 0);
27
28  SDL_Event event;
29  bool running = true;
30  auto lastTime = high_resolution_clock::now();
31
32  while (running) {
33    auto currentTime = high_resolution_clock::now();
34    duration<float> deltaTime =
35      currentTime - lastTime;
36    lastTime = currentTime;
37
38    while (SDL_PollEvent(&event)) {
39      if (event.type == SDL_MOUSEWHEEL) {
40        HandleMouseWheel(event.wheel);
41      }
42      if (event.type == SDL_QUIT) {
43        running = false;
44      }
45    }
46
47    scrollPosition += (
48      scrollVelocity * deltaTime.count());
49    scrollVelocity *= inertia;
50
51    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
52    SDL_RenderClear(renderer);
53
54    SDL_SetRenderDrawColor(
55      renderer, 255, 255, 255, 255);
56
57    SDL_Rect rect = {
58      375,
59      static_cast<int>(scrollPosition),
60      50,
61      50
62    };
63
64    SDL_RenderFillRect(renderer, &rect);
65
66    SDL_RenderPresent(renderer);
67  }
68
69  SDL_DestroyRenderer(renderer);
70  SDL_DestroyWindow(window);
71  SDL_Quit();
72  return 0;
73}