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:
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
character_stats (probably irrelevant, not used in-game)
PaperDollFrame.lua and PaperDollFrame.xml
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.