describe how extension data works

src/Player.hh

@@ -17,8 +17,35 @@
 
 struct PlayerBankItem;
 
+// PSO V2 stored some extra data in the character structs in a format that I'm
+// sure Sega thought was very clever for backward compatibility, but for us is
+// just plain annoying. Specifically, they used the third and fourth bytes of
+// the InventoryItem struct to store some things not present in V1. The game
+// stores arrays of bytes striped across these structures. In newserv, we call
+// those fields extension_data. They contain:
+//   items[0].extension_data1 through items[19].extension_data1:
+//       Extended technique levels. The values in the v1_technique_levels array
+//       only go up to 14 (tech level 15); if the player has a technique above
+//       level 15, the corresponding extension_data1 field holds the remaining
+//       levels (so a level 20 tech would have 14 in v1_technique_levels and 5
+//       in the corresponding item's extension_data1 field).
+//   items[0].extension_data2 through items[3].extension_data2:
+//       The value known as unknown_a1 in the PSOGCCharacterFile::Character
+//       struct. See SaveFileFormats.hh.
+//   items[4].extension_data2 through items[7].extension_data2:
+//       The timestamp when the character was last saved, in seconds since
+//       January 1, 2000. Stored little-endian, so items[4] contains the LSB.
+//   items[8].extension_data2 through items[12].extension_data2:
+//       Number of power materials, mind materials, evade materials, def
+//       materials, and luck materials (respectively) used by the player.
+//   items[13].extension_data2 through items[15].extension_data2:
+//       Unknown. These are not an array, but do appear to be related.
+
 struct PlayerInventoryItem { // 0x1C bytes
-  le_uint32_t present;
+  le_uint16_t present;
+  // See note above about these fields
+  uint8_t extension_data1;
+  uint8_t extension_data2;
   le_uint32_t flags; // 8 = equipped
   ItemData data;
 
@@ -125,7 +152,7 @@ struct PlayerDispDataDCPCV3 {
   /* 00 */ PlayerStats stats;
   /* 24 */ PlayerVisualConfig visual;
   /* 74 */ parray<uint8_t, 0x48> config;
-  /* BC */ parray<uint8_t, 0x14> technique_levels;
+  /* BC */ parray<uint8_t, 0x14> v1_technique_levels;
   /* D0 */
 
   // Note: This struct has a default constructor because it's used in a command