Adding Physics to Cursor Movement

1#include <SDL.h>
2#include <cmath>
3
4class PhysicsCursor {
5 public:
6  PhysicsCursor(
7    float maxSpeed = 1000.0f,
8    float acceleration = 2000.0f,
9    float friction = 5.0f
10  ) : MaxSpeed{maxSpeed},
11      Acceleration{acceleration},
12      Friction{friction} {}
13
14  void Update(float deltaTime) {
15    // Get real mouse position
16    int mouseX, mouseY;
17    SDL_GetMouseState(&mouseX, &mouseY);
18
19    // Calculate target vector
20    float targetX{
21      static_cast<float>(mouseX) - PosX};
22    float targetY{
23      static_cast<float>(mouseY) - PosY};
24
25    // Apply acceleration towards target
26    float distance{std::sqrt(
27      targetX * targetX + targetY * targetY)};
28
29    if (distance > 0.1f) {
30      float dirX{targetX / distance};
31      float dirY{targetY / distance};
32
33      VelX += dirX * Acceleration * deltaTime;
34      VelY += dirY * Acceleration * deltaTime;
35    }
36
37    // Apply friction
38    VelX *= std::pow(Friction, deltaTime);
39    VelY *= std::pow(Friction, deltaTime);
40
41    // Clamp velocity to max speed
42    float speed{std::sqrt(
43      VelX * VelX + VelY * VelY)};
44    if (speed > MaxSpeed) {
45      float scale{MaxSpeed / speed};
46      VelX *= scale;
47      VelY *= scale;
48    }
49
50    // Update position
51    PosX += VelX * deltaTime;
52    PosY += VelY * deltaTime;
53  }
54
55  void Render(SDL_Renderer* renderer) {
56    // Draw cursor at physics-controlled position
57    SDL_SetRenderDrawColor(
58      renderer, 255, 255, 255, 255);
59    SDL_Rect cursorRect{
60      static_cast<int>(PosX - 8),
61      static_cast<int>(PosY - 8),
62      16, 16
63    };
64    SDL_RenderFillRect(renderer, &cursorRect);
65  }
66
67 private:
68  float PosX{400.0f};  // Start at screen center
69  float PosY{300.0f};
70  float VelX{0.0f};
71  float VelY{0.0f};
72  float MaxSpeed;
73  float Acceleration;
74  float Friction;
75};

1int main() {
2  SDL_Init(SDL_INIT_VIDEO);
3  SDL_Window* window{SDL_CreateWindow(
4    "Physics Cursor",
5    SDL_WINDOWPOS_CENTERED,
6    SDL_WINDOWPOS_CENTERED,
7    800, 600, SDL_WINDOW_SHOWN
8  )};
9
10  SDL_Renderer* renderer{SDL_CreateRenderer(
11    window, -1, SDL_RENDERER_ACCELERATED)};
12
13  // Hide system cursor
14  SDL_ShowCursor(SDL_DISABLE);
15
16  PhysicsCursor cursor{500.0f, 2000.0f, 3.0f};
17
18  Uint32 lastTime{SDL_GetTicks()};
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    // Calculate delta time
30    Uint32 currentTime{SDL_GetTicks()};
31    float deltaTime{
32      (currentTime - lastTime) / 1000.0f};
33    lastTime = currentTime;
34
35    // Update and render
36    cursor.Update(deltaTime);
37
38    SDL_SetRenderDrawColor(
39      renderer, 0, 0, 0, 255);
40    SDL_RenderClear(renderer);
41
42    cursor.Render(renderer);
43
44    SDL_RenderPresent(renderer);
45  }
46
47  SDL_DestroyRenderer(renderer);
48  SDL_DestroyWindow(window);
49  SDL_Quit();
50  return 0;
51}