deferred block updates: falling sand

include/globals.h

@@ -74,6 +74,10 @@
 // Determines the fixed amount of memory allocated to blocks
 #define MAX_BLOCK_CHANGES 20000
 
+// How many "deferred" (happen at a later time than triggered) block updates to store.
+// Determines the fixed amount of memory allocated to that list
+#define MAX_DEFERRED_BLOCK_UPDATES 64
+
 // If defined, writes and reads world data to/from disk (or flash).
 // This is a synchronous operation, and can cause performance issues if
 // frequent random disk access is slow. Data is still stored in and
@@ -195,6 +199,13 @@ typedef struct {
   uint8_t block;
 } BlockChange;
 
+typedef struct {
+  short x;
+  short z;
+  uint8_t y;
+  uint8_t awaitTicks;
+} DeferredBlockUpdate;
+
 #pragma pack(push, 1)
 
 typedef struct {
@@ -267,6 +278,11 @@ typedef struct {
 extern BlockChange block_changes[MAX_BLOCK_CHANGES];
 extern int block_changes_count;
 
+extern DeferredBlockUpdate deferred_block_updates[MAX_DEFERRED_BLOCK_UPDATES];
+extern int deferred_block_updates_count;
+extern uint8_t is_processing_deferred_block_updates;
+extern uint8_t had_too_many_deferred_block_updates;
+
 extern PlayerData player_data[MAX_PLAYERS];
 extern int player_data_count;
 

include/procedures.h

@@ -44,6 +44,8 @@ void handlePlayerAction (PlayerData *player, int action, short x, short y, short
 void handlePlayerUseItem (PlayerData *player, short x, short y, short z, uint8_t face);
 
 void checkFluidUpdate (short x, uint8_t y, short z, uint8_t block);
+void processBlockUpdate (short x, uint8_t y, short z, uint8_t block);
+void deferBlockUpdate (short x, uint8_t y, short z, uint8_t awaitTicks);
 
 void spawnMob (uint8_t type, short x, uint8_t y, short z, uint8_t health);
 void interactEntity (int entity_id, int interactor_id);

src/globals.c

@@ -50,6 +50,11 @@ uint16_t client_count;
 BlockChange block_changes[MAX_BLOCK_CHANGES];
 int block_changes_count = 0;
 
+DeferredBlockUpdate deferred_block_updates[MAX_DEFERRED_BLOCK_UPDATES];
+int deferred_block_updates_count = 0;
+uint8_t is_processing_deferred_block_updates = 0;
+uint8_t had_too_many_deferred_block_updates = false;
+
 PlayerData player_data[MAX_PLAYERS];
 int player_data_count = 0;
 

src/main.c

@@ -595,6 +595,11 @@ int main () {
     // Check if it's time to yield to the idle task
     task_yield();
 
+    if (had_too_many_deferred_block_updates) {
+      printf("WARNING: Too many deferred block updates\n");
+      had_too_many_deferred_block_updates = 0;
+    }
+
     // Attempt to accept a new connection
     for (int i = 0; i < MAX_PLAYERS; i ++) {
       if (clients[i] != -1) continue;

src/procedures.c

@@ -1143,6 +1143,39 @@ void playPickupAnimation (PlayerData *player, uint16_t item, double x, double y,
 }
 #endif
 
+void processBlockUpdate (short x, uint8_t y, short z, uint8_t block) {
+  #ifdef DO_FLUID_FLOW
+    checkFluidUpdate(x, y, z, block);
+  #endif
+
+  if (isColumnBlock(block) && y) {
+    uint8_t below = getBlockAt(x, y - 1, z);
+    // TODO: if below block breaks sand
+    if (isReplaceableBlock(below)) {
+      // TODO: drop item of below block
+      makeBlockChange(x, y, z, 0);
+      makeBlockChange(x, y - 1, z, 0);
+      makeBlockChange(x, y - 1, z, block);
+      // update this (now moved) block and the block above next tick
+      deferBlockUpdate(x, y - 1, z, 0);
+      deferBlockUpdate(x, y + 1, z, 0);
+    }
+  }
+}
+
+void deferBlockUpdate (short x, uint8_t y, short z, uint8_t awaitTicks) {
+  if (deferred_block_updates_count == MAX_DEFERRED_BLOCK_UPDATES) {
+    had_too_many_deferred_block_updates = true;
+    return;
+  }
+
+  DeferredBlockUpdate *u = &deferred_block_updates[deferred_block_updates_count ++];
+  u->x = x;
+  u->y = y;
+  u->z = z;
+  u->awaitTicks = awaitTicks + is_processing_deferred_block_updates;
+}
+
 void handlePlayerAction (PlayerData *player, int action, short x, short y, short z) {
 
   // Re-sync slot when player drops an item
@@ -1192,29 +1225,13 @@ void handlePlayerAction (PlayerData *player, int action, short x, short y, short
     givePlayerItem(player, item, 1);
   }
 
-  // Update nearby fluids
+  // Update nearby blocks
   uint8_t block_above = getBlockAt(x, y + 1, z);
-  #ifdef DO_FLUID_FLOW
+  processBlockUpdate(x, y + 1, z, block_above);
-    checkFluidUpdate(x, y + 1, z, block_above);
+  processBlockUpdate(x - 1, y, z, getBlockAt(x - 1, y, z));
-    checkFluidUpdate(x - 1, y, z, getBlockAt(x - 1, y, z));
+  processBlockUpdate(x + 1, y, z, getBlockAt(x + 1, y, z));
-    checkFluidUpdate(x + 1, y, z, getBlockAt(x + 1, y, z));
+  processBlockUpdate(x, y, z - 1, getBlockAt(x, y, z - 1));
-    checkFluidUpdate(x, y, z - 1, getBlockAt(x, y, z - 1));
+  processBlockUpdate(x, y, z + 1, getBlockAt(x, y, z + 1));
-    checkFluidUpdate(x, y, z + 1, getBlockAt(x, y, z + 1));
-  #endif
-
-  // Check if any blocks above this should break, and if so,
-  // iterate upward over all blocks in the column and break them
-  uint8_t y_offset = 1;
-  while (isColumnBlock(block_above)) {
-    // Destroy the next block
-    makeBlockChange(x, y + y_offset, z, 0);
-    // Check for item drops *without a tool*
-    uint16_t item = getMiningResult(0, block_above);
-    if (item) givePlayerItem(player, item, 1);
-    // Select the next block in the column
-    y_offset ++;
-    block_above = getBlockAt(x, y + y_offset, z);
-  }
 }
 
 void handlePlayerUseItem (PlayerData *player, short x, short y, short z, uint8_t face) {
@@ -1361,11 +1378,11 @@ void handlePlayerUseItem (PlayerData *player, short x, short y, short z, uint8_t
     if (*count == 0) *item = 0;
     // Calculate fluid flow
     #ifdef DO_FLUID_FLOW
-      checkFluidUpdate(x, y + 1, z, getBlockAt(x, y + 1, z));
+      processBlockUpdate(x, y + 1, z, getBlockAt(x, y + 1, z));
-      checkFluidUpdate(x - 1, y, z, getBlockAt(x - 1, y, z));
+      processBlockUpdate(x - 1, y, z, getBlockAt(x - 1, y, z));
-      checkFluidUpdate(x + 1, y, z, getBlockAt(x + 1, y, z));
+      processBlockUpdate(x + 1, y, z, getBlockAt(x + 1, y, z));
-      checkFluidUpdate(x, y, z - 1, getBlockAt(x, y, z - 1));
+      processBlockUpdate(x, y, z - 1, getBlockAt(x, y, z - 1));
-      checkFluidUpdate(x, y, z + 1, getBlockAt(x, y, z + 1));
+      processBlockUpdate(x, y, z + 1, getBlockAt(x, y, z + 1));
     #endif
   }
 
@@ -1685,6 +1702,22 @@ void handleServerTick (int64_t time_since_last_tick) {
    */
   if (rng_seed == 0) rng_seed = world_seed;
 
+  // block updates might add more deferred block updates,
+  // so we temporarily make all new block updates add one more tick to the defer tick counter
+  is_processing_deferred_block_updates = 1;
+  int next_update_idx = 0;
+  for (int i = 0; i < deferred_block_updates_count; i ++) {
+    DeferredBlockUpdate *u = &deferred_block_updates[i];
+    if (u->awaitTicks) {
+      u->awaitTicks --;
+      deferred_block_updates[next_update_idx ++] = *u;
+    } else {
+      processBlockUpdate(u->x, u->y, u->z, getBlockAt(u->x, u->y, u->z));
+    }
+  }
+  deferred_block_updates_count = next_update_idx;
+  is_processing_deferred_block_updates = 0;
+
   // Tick mob behavior
   for (int i = 0; i < MAX_MOBS; i ++) {
     if (mob_data[i].type == 0) continue;

src/serialize.c

@@ -16,6 +16,8 @@
 
 int64_t last_disk_sync_time = 0;
 
+// TODO: store deferred block updates
+
 // Restores world data from disk, or writes world file if it doesn't exist
 int initSerializer () {