Creating Cursor Trail Effects

1#include <SDL.h>
2#include <deque>
3#include <cmath>
4
5struct TrailPoint {
6  int x, y;
7  Uint32 timestamp;
8};
9
10class CursorTrail {
11public:
12  static constexpr size_t MAX_POINTS{20};
13  static constexpr Uint32 TRAIL_DURATION{500};// milliseconds
14
15  void Update(int mouseX, int mouseY) {
16    auto now{SDL_GetTicks()};
17
18    // Add new point
19    TrailPoints.push_front({mouseX, mouseY, now});
20
21    // Remove old points
22    while (!TrailPoints.empty() &&
23           now - TrailPoints.back().timestamp > TRAIL_DURATION) {
24      TrailPoints.pop_back();
25    }
26
27    // Limit total points
28    while (TrailPoints.size() > MAX_POINTS) {
29      TrailPoints.pop_back();
30    }
31  }
32
33  void Render(SDL_Renderer* renderer) {
34    auto now{SDL_GetTicks()};
35
36    // Render trail points
37    for (size_t i{1}; i < TrailPoints.size(); ++i) {
38      const auto& current{TrailPoints[i - 1]};
39      const auto& prev{TrailPoints[i]};
40
41      // Calculate alpha based on age
42      float age{static_cast<float>(
43        now - current.timestamp) / TRAIL_DURATION
44      };
45      Uint8 alpha{static_cast<Uint8>(
46        255 * (1.0f - age)
47      )};
48
49      SDL_SetRenderDrawBlendMode(
50        renderer, SDL_BLENDMODE_BLEND);
51      SDL_SetRenderDrawColor(
52        renderer, 255, 255, 255, alpha);
53
54      SDL_RenderDrawLine(
55        renderer,
56        current.x, current.y,
57        prev.x, prev.y
58      );
59    }
60  }
61
62private:
63  std::deque<TrailPoint> TrailPoints;
64};

1#include <SDL.h>
2#include <iostream>
3
4int main() {
5  SDL_Init(SDL_INIT_VIDEO);
6
7  SDL_Window* window{SDL_CreateWindow(
8    "Cursor Trail",
9    SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
10    800, 600,
11    SDL_WINDOW_SHOWN
12  )};
13
14  SDL_Renderer* renderer{SDL_CreateRenderer(
15    window, -1, SDL_RENDERER_ACCELERATED
16  )};
17
18  CursorTrail trail;
19  bool running{true};
20
21  while (running) {
22    SDL_Event event;
23    while (SDL_PollEvent(&event)) {
24      if (event.type == SDL_QUIT) {
25        running = false;
26      }
27    }
28
29    // Update trail
30    int mouseX, mouseY;
31    SDL_GetMouseState(&mouseX, &mouseY);
32    trail.Update(mouseX, mouseY);
33
34    // Render
35    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
36    SDL_RenderClear(renderer);
37
38    trail.Render(renderer);
39
40    SDL_RenderPresent(renderer);
41  }
42
43  SDL_DestroyRenderer(renderer);
44  SDL_DestroyWindow(window);
45  SDL_Quit();
46  return 0;
47}