Breakable objects

Things to remember:

This article represents work-in-progress and does not necessarily reflect the current working state of the code!

Introduction

This article deals with details in regarding of breaking single objects apart in the physics simulation.

For breaking the connection between bound objects, please see the article about breakable bonds.

How to Destroy Objects

When the force acting on one entity becomes very strong, it should be destroyed. This can happen while the entity is still bound to another entity, or after they have become unbound.

Currently, there are two ways to denote that an entity should be destroyed/broken upon death:

Setting health

By setting the following spawnargs on one entity:

       "health"                        "20"

the entity will be destroyed when the health drops to 0.

The health sets the amount of damage that needs to be done to the object until it breaks.

Drawbacks of this method are that health can drop by small forces acting on the entity. After the health has dropped considerable, a small force can then suddenly break the object. For instance, damaging a wine bottle by 9 points 2 times would leave the bottle with only 2 points health, and thus suddenly a damage of 2 points can destroy the bottle.

Another drawback is that forces do not translate into damage except in some specially coded exceptions, like hits from weapons or movers that damage entities.

Setting max_stress or max_torque

When the forces acting on a moveable entity exceed these values, the entity breaks:

       "max_stress"                        "50 50 200"
       "max_torque"                        "10 10 100"

What happens when an entity dies?

Depending on which spawnarg is set, different things happen when an entity is broken:

broken

Setting:

       "broken"                        "models/darkmod/junk/wbottle01_broken.lwo"

The broken sets the model that will replace the default model after the destruction. The entity itself will stay around, but it cannot be damaged any further.

def_broken, broken_offset, broken_probability and broken_count

TODO: Rename these to def_flinder, flinder_offset, flinder_probability and flinder_count.

Setting:

       "def_broken"               "models/darkmod/junk/wbottle01_broken.lwo"
       "broken_offset"            "0 0 -5"
       "def_broken1"              "models/darkmod/junk/glass_shard.lwo"
       "broken_count1"            "6"

will result in the bottle spawn one broken lower half bottle, and 6 glass shards. The original entity will be removed from the world automatically.

broken_offset, broken_probability and broken_count are optional.

Todo

TODO

• Except wine bottles, no object breaks when a sufficient force acts on it.
• Strong forces do not nec. damage entities. For instance dropping a crate on a bottle does not break the bottle.
• Damage needs to be calculated from the impulse, not from a fixed set of "damage" values.

See also

• Breakable bonds
• http://en.wikipedia.org/wiki/Lever
• http://en.wikipedia.org/wiki/moment_%28physics%29