[WoTLK][HELP] Custom School and Resistance Issues

[Aentium 0]

What I'm intending to do: 

To learn how to create custom schools of magic and resistances and apply them to spells, items, creatures and characters and share it with the community.

What I've managed to do so far:

I've made the school and resistance work at its most basic level combat-wise: the damage dealt is from its own distinct school ('Custom') and can be reduced with resistances, modified with 'Custom' spell power, 'Custom' crit chance, etc.

I've edited the following files:

Core

• SharedDefines.h -> lines 301 - 334
• CharacterDatabase.cpp -> lines 530 - 532
• ThreatManager.cpp -> lines 637 - 639
• Creature.cpp -> line 596
• ItemTemplate.cpp -> line 230
• ItemTemplate.h -> line 653
• Player.cpp -> lines 7596 - 7597 | line 20357
• Unit.cpp -> lines 9073 & 9208 | 13264, 13265
• Unit.h -> line 170 & 181
• ObjectMgr.cpp -> line 2816 | lines 2910 - 2963
• enuminfo_SharedDefines.cpp -> line 171 | 191
• UpdateFieldFlags.cpp -> lines 126, 136,  270, 278, 286 | 156 - 175 | 354 - 392 | 1345, 1353

DB

• character_stats (probably irrelevant, not used in-game)
• item_template

DBC

• Resistances.dbc

Interface

• Constants.lua
• GlobalStrings.lua
• PaperDollFrame.lua and PaperDollFrame.xml

The issues:

There are a lot of issues, most of them possibly linked to the same unknown cause:

• All item icons are invisible to the client and their tooltips are distorted. Unsurprisingly, the distorted fields are those following the edited column in the database (look at the attack delay or the item message). However, all items still exist and work as usual: weapons determine your damage (although you appear to be unarmed), armor is visible on your character and reduces physical damage taken, items take space in bags, etc.

• A lot of NPCs are also invisible or have missing textures. Some unexplicably so, as another instance of the same creature has the correct texture. Players can also appear invisible, although targetable if you press tab or if attacked.

• Spell tooltips display mana costs in the billions, while the spells actually cost their blizzlike amounts.

• This one might be due to my absolute inexperience working with interfaces, but the amount of 'Custom' resistance is not displayed and the the slot is instead filled with the default X. Also, the spell tab just below the character model doesn't work and gets stuck at Bonus Damage (most likely because it was edited to display the Custom Bonus Damage when moused-over like the rest of schools.

 

I've been dealing with this issue for quite a while. It wasn't until recently that I decided to give it another shot, but it's still the same. I really think the custom community can benefit from cracking this issue down and, if necessary, I can upload the code I changed from the core files to check if everything's ok.