improve block placement checks

src/packets.c

@@ -523,8 +523,13 @@ int cs_useItemOn (int client_fd) {
 
   // check if the block's placement conditions are met
   if (
-    !(x == player->x && (y == player->y || y == player->y + 1) && z == player->z) &&
-    (getBlockAt(x, y, z) == B_air) &&
+    !( // player is not in the way
+      !isPassableBlock(block) &&
+      x == player->x &&
+      (y == player->y || y == player->y + 1) &&
+      z == player->z
+    ) &&
+    isReplaceableBlock(getBlockAt(x, y, z)) &&
     (!isColumnBlock(block) || getBlockAt(x, y - 1, z) != B_air)
   ) {
     // decrease item amount in selected slot

src/procedures.c

@@ -435,7 +435,6 @@ uint8_t isInstantlyMined (PlayerData *player, uint8_t block) {
 
 // Checks whether the given block has to have something beneath it
 uint8_t isColumnBlock (uint8_t block) {
-
   return (
     block == B_snow ||
     block == B_moss_carpet ||
@@ -445,20 +444,29 @@ uint8_t isColumnBlock (uint8_t block) {
     block == B_sand ||
     block == B_torch
   );
-
 }
 
+// Checks whether the given block is non-solid
 uint8_t isPassableBlock (uint8_t block) {
-
   return (
     block == B_air ||
     block == B_water ||
+    block == B_snow ||
     block == B_moss_carpet ||
     block == B_short_grass ||
     block == B_dead_bush ||
     block == B_torch
   );
+}
 
+// Checks whether the given block can be replaced by another block
+uint8_t isReplaceableBlock (uint8_t block) {
+  return (
+    block == B_air ||
+    block == B_water ||
+    block == B_short_grass ||
+    block == B_snow
+  );
 }
 
 void handlePlayerAction (PlayerData *player, int action, short x, short y, short z) {