Spawn Points

When spawning enemies on both the overworld and in dungeons, the game will pick a spawn point for each of 9 object slots, regardless of the number of objects on that screen. Spawns are picked from one of 4 sets of 9 spawns, chosen based on the direction Link is facing when entering the screen. It increments the spawn index counter (which is mod 9 and stored at address $524) each time it picks a spawn for a slot. If the spawn is on a solid block or too close to link (within #$22 pixels X and Y, exclusive, treating objects as points), it's ruled invalid and a new spawn is picked for the same object, repeating the process of incrementing and checking. The spawn counter seems to only be cleared on reset; not even quitting the game and selecting a different save file will clear it.

When entering a cave, Link's position and direction when he entered the cave are used, not his position and direction at the bottom of the screen. Because of this, entering a cave from different directions can change the spawns. When exiting a cave, his new position and direction on the overworld screen are used.

The spawn counter is not changed on screens with no active objects (there are none or they're all dead; dungeon room treasures are ignored), screens with objects that spawn from the edges (excluding rocks; the rock generator is spawned like normal), screens with only a live Zora object, side-view screens, and the screen with Zelda.

Examples:
-If there are no invalid spawns on a screen, the spawn index counter is increased by 9, which returns it to the same value.
-If the spawn index counter is at 0 and index 8 is an invalid spawn, that last object slot will fail once and use index 0, instead, and the counter will end up at 1.
-If the spawn index counter is at 0 and indices 0 and 1 are invalid spawns, the first object slot will fail twice and use index 2, the second to last object slot will also fail twice and use index 2, and the last slot will use index 3, leaving the counter at 4.


Below are the spawn diagrams, with commas indicating dungeon walls. The numbers indicate the spawn index, and spawns are picked sequentially.

Facing Right:
 X 0 1 2 3 4 5 6 7 8 9 A B C D E F
Y-----------------------------------
3| , , , , , , , , , , , , , , , , |
4| , , , , , , , , , , , , , , , , |
5| , , . . . 0 . . . . . . . . , , |
6| , , . . . . . . . . . . 6 . , , |
7| , , . . . . . . 2 . 4 . . . , , |
8| , , . . . . . . . . . . . 8 , , |
9| , , . . . . . . 3 . 5 . . . , , |
A| , , . . . . . . . . . . 7 . , , |
B| , , . . . 1 . . . . . . . . , , |
C| , , , , , , , , , , , , , , , , |
D| , , , , , , , , , , , , , , , , |
 -----------------------------------

Facing Left:
 X 0 1 2 3 4 5 6 7 8 9 A B C D E F
Y-----------------------------------
3| , , , , , , , , , , , , , , , , |
4| , , , , , , , , , , , , , , , , |
5| , , . . . . . . . . 7 . . . , , |
6| , , . 1 . . . . . . . . . . , , |
7| , , . . . 3 . 5 . . . . . . , , |
8| , , 0 . . . . . . . . . . . , , |
9| , , . . . 4 . 6 . . . . . . , , |
A| , , . 2 . . . . . . . . . . , , |
B| , , . . . . . . . . 8 . . . , , |
C| , , , , , , , , , , , , , , , , |
D| , , , , , , , , , , , , , , , , |
 -----------------------------------

Facing Down:
 X 0 1 2 3 4 5 6 7 8 9 A B C D E F
Y-----------------------------------
3| , , , , , , , , , , , , , , , , |
4| , , , , , , , , , , , , , , , , |
5| , , . . . . . . . . . . . . , , |
6| , , . . . . . . . . . . . . , , |
7| , , . . . 1 . . . . 6 . . . , , |
8| , , . . . . . 4 . . . . . . , , |
9| , , . . . . 3 . . 5 . . . . , , |
A| , , . 0 . . . . . . . . 8 . , , |
B| , , . . . 2 . . . . 7 . . . , , |
C| , , , , , , , , , , , , , , , , |
D| , , , , , , , , , , , , , , , , |
 -----------------------------------

Facing Up:
 X 0 1 2 3 4 5 6 7 8 9 A B C D E F
Y-----------------------------------
3| , , , , , , , , , , , , , , , , |
4| , , , , , , , , , , , , , , , , |
5| , , . . . 1 . . . . 6 . . . , , |
6| , , . 0 . . . . . . . . 8 . , , |
7| , , . . . . 3 . . 5 . . . . , , |
8| , , . . . . . . 4 . . . . . , , |
9| , , . . . 2 . . . . 7 . . . , , |
A| , , . . . . . . . . . . . . , , |
B| , , . . . . . . . . . . . . , , |
C| , , , , , , , , , , , , , , , , |
D| , , , , , , , , , , , , , , , , |
 -----------------------------------