mangosR2/mangos — comment on commit c9819d38012ba6568a0438c68075523766a4d011
File:  line 0
By Zakamurite:

Heartbeat resistance is strongly dependent on binary resistance.
In R2 and clean mangos core resistance only affects amount of damage that will be mitigated on hit.
There are binary spells (that deal damage, Frostbolt, Fireball, etc) and non-binary (that apply aura only, e.g. Polymorph, Fear, Counterspell, Cyclone, etc).
First of all, mitigated damage is calculated, and then (if spell is non-binary) spell hit chance should be calculated. In this case, the bigger resistance target has, the lesser chance will be that spell will hit.

As there is no binary resistance implemented, this commit only will take into account auras that increase/decrease resistances, but not actual resistances. Also in Aura::PeriodicCheck() need check for binary spells.

http://www.wowpedia.org/Resistance