Fixed vs Variable Time Step

The choice between fixed and variable time steps in game development can significantly impact your game's behavior, performance, and complexity. Let's explore the pros and cons of each approach:

In a fixed time step system, the game updates at regular, predetermined intervals.

Pros:

1. Consistency: Game logic and physics behave predictably across different hardware.
2. Simplicity: Easier to implement and reason about, especially for physics simulations.
3. Determinism: Useful for networking and replays, as the game state is more easily reproducible.

Cons:

1. Performance overhead: May need to run multiple updates to catch up if frame rate drops.
2. Less smooth on variable frame rate displays.
3. Can waste CPU time if updates are faster than necessary.

Here's a basic implementation of a fixed time step:

1#include <SDL.h>
2
3// 60 updates per second
4const float FIXED_DT = 1.0f / 60.0f;
5
6void update(float dt) {
7  // Game update logic here
8}
9
10void render() {
11  // Rendering logic here
12}
13
14int main() {
15  SDL_Init(SDL_INIT_VIDEO);
16  float accumulator = 0.0f;
17  Uint64 currentTime = SDL_GetTicks64();
18
19  while (true) {
20    Uint64 newTime = SDL_GetTicks64();
21    float frameTime = (newTime - currentTime) /
22      1000.0f;
23    currentTime = newTime;
24
25    accumulator += frameTime;
26
27    while (accumulator >= FIXED_DT) {
28      update(FIXED_DT);
29      accumulator -= FIXED_DT;
30    }
31
32    render();
33  }
34
35  SDL_Quit();
36  return 0;
37}

In a variable time step system, the game updates based on the actual elapsed time between frames.

Pros:

1. Smoothness: Can take advantage of high refresh rate displays.
2. Efficiency: No need to run multiple updates to catch up.
3. Simplicity in main loop: No need for time accumulation or multiple update calls per frame.

Cons:

1. Inconsistency: Game behavior might vary slightly on different hardware.
2. Complexity in game logic: Need to account for variable dt in all time-dependent calculations.
3. Potential for physics instability with large time steps.

Here's a basic implementation of a variable time step:

1#include <SDL.h>
2
3void update(float dt) {
4  // Game update logic here
5}
6
7void render() {
8  // Rendering logic here
9}
10
11int main() {
12  SDL_Init(SDL_INIT_VIDEO);
13  Uint64 currentTime = SDL_GetTicks64();
14
15  while (true) {
16    Uint64 newTime = SDL_GetTicks64();
17    float dt = (newTime - currentTime) /
18      1000.0f;
19    currentTime = newTime;
20
21    update(dt);
22    render();
23  }
24
25  SDL_Quit();
26  return 0;
27}

Some games use a hybrid approach, using fixed time steps for physics and gameplay logic, but variable time steps for animations and rendering. This can provide the benefits of both systems.

In conclusion, the choice between fixed and variable time steps depends on your game's specific requirements. Fixed time steps are often preferred for games requiring precise physics or deterministic behavior, while variable time steps can be beneficial for games that prioritize visual smoothness and efficiency on a wide range of hardware.