Syncing Timers in Multiplayer

1#include <SDL.h>
2
3#include <iostream>
4
5class NetworkSpawner {
6public:
7  struct SpawnConfig {
8    Uint32 StartTime;
9    Uint32 Interval;
10    int WaveSize;
11  };
12
13  void StartSpawning(
14    const SpawnConfig& Config) {
15    MyConfig = Config;
16    IsSpawning = true;
17    LastSpawnTime = Config.StartTime;
18
19    std::cout << "Starting wave at time "
20      << Config.StartTime << "ms\n";
21  }
22
23  void Update() {
24    if (!IsSpawning) { return; }
25
26    Uint32 CurrentTime{SDL_GetTicks()};
27    Uint32 TimeSinceStart{
28      CurrentTime - MyConfig.StartTime};
29    Uint32 ExpectedSpawns{
30      TimeSinceStart / MyConfig.Interval};
31
32    // Spawn any missing enemies to catch up
33    while (SpawnCount < ExpectedSpawns &&
34      SpawnCount < MyConfig.WaveSize) {
35      SpawnEnemy(CurrentTime);
36      SpawnCount++;
37    }
38
39    // Check if wave is complete
40    if (SpawnCount >= MyConfig.WaveSize) {
41      IsSpawning = false;
42    }
43  }
44
45private:
46  void SpawnEnemy(Uint32 Time) {
47    std::cout << "Spawning enemy at time "
48      << Time << "ms\n";
49    LastSpawnTime = Time;
50  }
51
52  SpawnConfig MyConfig;
53  bool IsSpawning{false};
54  Uint32 LastSpawnTime{0};
55  Uint32 SpawnCount{0};
56};
57
58// Simulate network message received from server
59void HandleServerMessage(
60  NetworkSpawner& Spawner) {
61  NetworkSpawner::SpawnConfig Config;
62  Config.StartTime = SDL_GetTicks();
63  Config.Interval = 1000;
64  Config.WaveSize = 3;
65  Spawner.StartSpawning(Config);
66}
67
68int main(int argc, char** argv) {
69  SDL_Init(SDL_INIT_TIMER);
70
71  NetworkSpawner Spawner;
72  HandleServerMessage(Spawner);
73
74  // Simulate game loop
75  for (int i = 0; i < 4; ++i) {
76    Spawner.Update();
77    SDL_Delay(1000);
78  }
79
80  SDL_Quit();
81  return 0;
82}