add "on_collision" callbacks for entities

[MarkuBu]

I propose to add two functions for entities

• on_entity_collision()
  If two entities collide the callback from both entities is called with a reference to the other entity

• on_node_collision()
  this callback is called every time an entity hits a new node. So if an entity doesn't moves over the surface this callback wouldn't be called. If an entity enters a new node or hits a node in front the callback is called with the pos of the node

I think this would be very useful for mods like bows and arrows or for mobs

[Desour]

It would be very useful if it can be done without much lag.

[rubenwardy]

this would be a nice feature, especially if done in a way that players can also use it. A few mods, eg: mesecons, currently use on_globalstep to detect if a player is stepping on a node.

[raymoo]

@rubenwardy
I think the overhead of using on_globalstep for that purpose is not very high, provided all "stepping" handlers are dispatched to by a single globalstep (ideally a central mod that allows registering these handlers, but one globalstep per mod that wants the behavior would be ok in my opinion).

[Wuzzy2]

This is very important for anything dynamic. There is an almost infinite number of use cases for this, some examples were posted before.

[SmallJoker]

Related issues:

• on_entity_collision()
  Duplicate, requested in on_collide for entity #3918, on_collide for entity

• on_node_collision()
  Opposite direction, for nodes, but relies on the same code area: on_walk_over() for nodes (or better, on_new_standing_node() for players) #247, on_walk_over()

[xunto]

We really need this callback. I looked through some "archery" mods and all of them check collision using on_step callback, some of them even calculate collisions with collisions boxes, while obviously this work already done in core (physical = true and collide_with_objects = true). I tried tracking speed changes with physical = true to notice collisions, it worked but looked hacky.

[paramat]

@SmallJoker is working on a bows mod that uses raycast to detect objects on the shoot line.

[MarkuBu]

Well, that might work, but I think that doesn't help for many other use cases. Arrows are small objects. A raycast may work. How many rays do you want to cast if you have bigger objects?

[paramat]

Yes, i was just replying to xunto's usecase.

[xunto]

@paramat Hmm, maybe I should try it. Even though I've already written collision check in lua for my spellcasting mod.

[SmallJoker]

@paramat Please note that raycast does not handle collisions (walkable and collision box values) and is more suitable to get a pointed thing with a direction and position given. For bigger objects, each collision box edge would have to be cast, which seems to be more hacky than simply using the physical attribute in combination with the velocity it had before colliding.

[rubenwardy]

duplicate of #3918