Shield durability

Shields lose durability points every time damage is taken and blocked and also during shield surfing.

Attack blocking

The logic is as follows:

float damageRatio = GlobalParameter::sInstance->globalParam->shieldDamageRatio.value();
int damage = damageRatio * (param->attackPower - guardPower - additionalGuardPower);
if (param->forceOnlyOneDamage)
  minDamage = 1;
else
  minDamage = param->minDmg;
weapon->takeDamage(min(damage, minDamage));

• damageRatio is loaded from GlobalParameter ("ShieldDamageRatio" in the "Global" section).
• attackPower is the power of the attack that is being blocked by the shield.
• guardPower is the base Guard Power of the shield. It is loaded from the shield's bgparamlist ("GuardPower" in the "WeaponCommon" section).
• additionalGuardPower is the Shield Guard Up bonus value (if any).

minDmg appears to be 1 in most cases.

In 1.6.0, ShieldDamageRatio is 0.2, meaning a shield takes a minimum of 1 damage point (in most cases), and 1 damage point for every 5 points of difference between the attack power and the guard power.

Shield surfing

The shield surf damage logic is available here: https://gist.github.com/leoetlino/34a2ce6273f7cfcbbabceda24d19aa5d

Here is a gist of the logic:

• Whenever Link is shield surfing, a timer (which is tied to the shield) is incremented.
• If Link is surfing on a "no shield damage floor", or if the L2 norm of his velocity is lower than 0.03, then the shield takes no damage.
• Otherwise, every time the timer reaches ShieldRideBaseFrame (as configured in GlobalParameter), the shield takes RideBreakRatio * ShieldRideHitBaseDamage * Damage and the timer is reset.

In 1.6.0:

• RideBreakRatio is 1.0 for the majority of shields, and 0.2 for the Ancient Shield, which means that the latter takes shield surfing damage at a 20% rate compared to most other shields.

• ShieldRideBaseFrame is 120 and ShieldRideHitBaseDamage is 1. This means that shield surfing costs RideBreakRatio * 1 durability points every 4 seconds.