defs: Tiles now have an offset to refer to a head tile

This head tile is used to point to a tile that manages to overall state
of multi-tile structures.

diff --git a/src/defs.s b/src/defs.s
index 472bc9c60a729684e18bd60abab423b395766286..a8452232ee3c4d88182753be0f2554ed01f55067 100644 (file)
--- a/src/defs.s
+++ b/src/defs.s
@@ -43,4 +43,10 @@
 .de c_fire, 1
 .de c_occupation, 1
 .de c_other, 2
+  ; offset to head tile for thsi tile
+  ; if offset is 0000 this is the head tile 
+  ; head tiles are tiles that manage the state of a 
+  ; multi-tile object
+  ; the head tile is located at c_type - [c_head_offset]
+.de c_head_offset, 2
 .de c_size, 0