add option to tie movement updates to tickrate

include/globals.h

@@ -102,9 +102,18 @@
 // clients from Keep Alive packets.
 #define NETWORK_TIMEOUT_TIME 15000000
 
+// If defined, rebroadcasts ALL incoming movement updates, disconnecting
+// movement from the server's tickrate. This makes movement much smoother
+// on very low tickrates, at the cost of potential network instability when
+// hosting more than just a couple of players. When disabling this on low
+// tickrates, consider disabling SCALE_MOVEMENT_UPDATES_TO_PLAYER_COUNT too.
+#define BROADCAST_ALL_MOVEMENT
+
 // If defined, scales the frequency at which player movement updates are
 // broadcast based on the amount of players, reducing overhead for higher
 // player counts. For very many players, makes movement look jittery.
+// It is not recommended to use this if BROADCAST_ALL_MOVEMENT is disabled
+// on low tickrates, as that might drastically decrease the update rate.
 #define SCALE_MOVEMENT_UPDATES_TO_PLAYER_COUNT
 
 // If defined, calculates fluid flow when blocks are updated near fluids
@@ -207,6 +216,7 @@ typedef struct {
   // 0x08 - sprinting
   // 0x10 - eating, makes flagval_16 act as eating timer
   // 0x20 - client loading, uses flagval_16 as fallback timer
+  // 0x40 - movement update cooldown
   uint8_t flags;
 } PlayerData;
 

src/main.c

@@ -233,17 +233,31 @@ void handlePacket (int client_fd, int length, int packet_id, int state) {
           player->pitch = pitch / 90.0f * 127.0f;
         }
 
-        // Broadcast player position to other players
+        // Whether to broadcast player position to other players
+        uint8_t should_broadcast = true;
+
+        #ifndef BROADCAST_ALL_MOVEMENT
+          // If applicable, tie movement updates to the tickrate by using
+          // a flag that gets reset on every tick. It might sound better
+          // to just make the tick handler broadcast position updates, but
+          // then we lose precision. While position is stored using integers,
+          // here the client gives us doubles and floats directly.
+          should_broadcast = !(player->flags & 0x40);
+          if (should_broadcast) player->flags |= 0x40;
+        #endif
+
         #ifdef SCALE_MOVEMENT_UPDATES_TO_PLAYER_COUNT
           // If applicable, broadcast only every client_count-th movement update
-          uint8_t should_broadcast = false;
-          if (++player->packets_since_update >= client_count) {
-            should_broadcast = true;
+          if (++player->packets_since_update < client_count) {
+            should_broadcast = false;
+          } else {
+            // Note that this does not explicitly set should_broadcast to true
+            // This allows the above BROADCAST_ALL_MOVEMENT check to compound
+            // Whether that's ever favorable is up for debate
             player->packets_since_update = 0;
           }
-        #else
-          #define should_broadcast (client_count > 0)
         #endif
+
         if (should_broadcast) {
           // If the packet had no rotation data, calculate it from player data
           if (packet_id == 0x1D) {

src/procedures.c

@@ -1424,6 +1424,11 @@ void handleServerTick (int64_t time_since_last_tick) {
         player->flagval_16 = 0;
       } else player->flagval_16 ++;
     }
+    // Reset movement update cooldown if not broadcasting every update
+    // Effectively ties player movement updates to the tickrate
+    #ifndef BROADCAST_ALL_MOVEMENT
+      player->flags &= ~0x40;
+    #endif
     // Below this, process events that happen once per second
     if (server_ticks % (uint32_t)TICKS_PER_SECOND != 0) continue;
     // Send Keep Alive and Update Time packets