From b020cec224b104925b43770f2cb53305f0d89034 Mon Sep 17 00:00:00 2001
From: p2r3 <p2r3@p2r3.com>
Date: Sat, 23 Aug 2025 02:13:51 +0300
Subject: [PATCH] fix mobs spawning at bad Y coordinate

---
 include/procedures.h |  3 +++
 src/main.c           | 42 ++++++++++++++++++++++++++----------------
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/include/procedures.h b/include/procedures.h
index 33dcaee..888d46d 100644
--- a/include/procedures.h
+++ b/include/procedures.h
@@ -27,6 +27,9 @@ void makeBlockChange (short x, uint8_t y, short z, uint8_t block);
 
 uint8_t isInstantlyMined (PlayerData *player, uint8_t block);
 uint8_t isColumnBlock (uint8_t block);
+uint8_t isPassableBlock (uint8_t block);
+uint8_t isReplaceableBlock (uint8_t block);
+
 uint16_t getMiningResult (uint16_t held_item, uint8_t block);
 void bumpToolDurability (PlayerData *player);
 void handlePlayerAction (PlayerData *player, int action, short x, short y, short z);
diff --git a/src/main.c b/src/main.c
index a3c95e8..dbfe484 100644
--- a/src/main.c
+++ b/src/main.c
@@ -266,22 +266,32 @@ void handlePacket (int client_fd, int length, int packet_id) {
           // at a random position within the chunk
           short mob_x = (_x + dx * VIEW_DISTANCE) * 16 + ((r >> 4) & 15);
           short mob_z = (_z + dz * VIEW_DISTANCE) * 16 + ((r >> 8) & 15);
-          uint8_t mob_y = getHeightAt(mob_x, mob_z) + 1;
-          // Ensure that there's space to spawn the mob
-          if (
-            getBlockAt(mob_x, mob_y, mob_z) == B_air &&
-            getBlockAt(mob_x, mob_y + 1, mob_z) == B_air
-          ) {
-            // Spawn passive mobs during the day, hostiles during the night
-            if (world_time < 13000) {
-              uint32_t mob_choice = (r >> 12) & 3;
-              if (mob_choice == 0) spawnMob(25, mob_x, mob_y, mob_z, 20); // Chicken
-              else if (mob_choice == 1) spawnMob(28, mob_x, mob_y, mob_z, 20); // Cow
-              else if (mob_choice == 2) spawnMob(95, mob_x, mob_y, mob_z, 20); // Pig
-              else if (mob_choice == 3) spawnMob(106, mob_x, mob_y, mob_z, 20); // Sheep
-            } else {
-              spawnMob(145, mob_x, mob_y, mob_z, 20); // Zombie
-            }
+          // Start at the Y coordinate of the spawning player and move upward
+          // until a valid space is found
+          uint8_t mob_y = cy;
+          uint8_t b_low = getBlockAt(mob_x, mob_y - 1, mob_z);
+          uint8_t b_mid = getBlockAt(mob_x, mob_y, mob_z);
+          uint8_t b_top = getBlockAt(mob_x, mob_y + 1, mob_z);
+          while (mob_y < 255) {
+            if ( // Solid block below, non-solid at feet and above
+              !isPassableBlock(b_low) &&
+              isPassableBlock(b_mid) &&
+              isPassableBlock(b_top)
+            ) break;
+            b_low = b_mid;
+            b_mid = b_top;
+            b_top = getBlockAt(mob_x, mob_y + 2, mob_z);
+            mob_y ++;
+          }
+          // Spawn passive mobs during the day, hostiles during the night
+          if (world_time < 13000) {
+            uint32_t mob_choice = (r >> 12) & 3;
+            if (mob_choice == 0) spawnMob(25, mob_x, mob_y, mob_z, 20); // Chicken
+            else if (mob_choice == 1) spawnMob(28, mob_x, mob_y, mob_z, 20); // Cow
+            else if (mob_choice == 2) spawnMob(95, mob_x, mob_y, mob_z, 20); // Pig
+            else if (mob_choice == 3) spawnMob(106, mob_x, mob_y, mob_z, 20); // Sheep
+          } else {
+            spawnMob(145, mob_x, mob_y, mob_z, 20); // Zombie
           }
         }