Pathos

Gaspunk bundles a pseudo-library called Pathos. What this means is that it is technically a part of the mod but everything is setup to allow a painless split in case another mod unrelated to gaspunk would need it.

Sicknesses

The goal of Pathos is to provide a simple API to add sicknesses. A sickness is basically a potion effect with no predefined duration and a variable severity.

Adding Sicknesses

Like gases, sicknesses have their own registry, so you can register your own sicknesses through the event:

@SubscribeEvent
public void addSicknesses(RegistryEvent.Register<ISickness> event) {   
    event.getRegistry().register(new MySickness().setRegistryName(YourMod.MOD_ID, "cancer")); 
}

This also means that the ObjectHolder annotation is compatible with sicknesses.

The class needs to implement ISickness, which has a single required method, performEffect. This method is the equivalent to the eponymous method in the Potion class. It is called each tick when an entity is afflicted by your sickness, with a reference to the entity and the carried SicknessEffect. This effect gives you access to various informations like the number of ticks since the effect was contracted or the current severity of the effect. The method returns true if a real effect was performed. What can be considered a real effect is left to the implementation. In essence, a return value of true resets the ticksSinceLastPerform timer on the effect. This timer is mostly intended as a convenience (it is not used anywhere by default) though it should remain meaningful as other mechanisms could use it.

Using Sicknesses

To afflict a living entity with a sickness, simply create a new SicknessEffect with the desired ISickness and severity and add it to the entity's ISicknessHandler capability. Ex:

@CapabilityInject(ISicknessHandler.class)
public static Capability<ISicknessHandler> CAPABILITY_SICKNESS;

public void addCancerToEntity(EntityLivingBase entity) {
    ISicknessHandler handler = entity.getCapability(CAPABILITY_SICKNESS, null);
    SicknessEffect effect = new SicknessEffect(ModSicknesses.CANCER, 0.6f);
    handler.addSickness(effect);
}