Propper use of ShouldCollide

[edgarasf123]

How exactly should one use [URL="https://wiki.garrysmod.com/page/GM/ShouldCollide"]ShouldCollide[/URL] hook? Because everytime I try to use it, it breaks the physics, or crashes the server... We need better documentation! Also it doesn't break the physics instantly, but it happens overtime...

[B]For example: [/B]
This code breaks the physics

someEntity:SetCustomCollisionCheck( true )
local ncProp = {} -- Just a table of random props
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
  if not ncProp[ent1] and not ncProp[ent2] then return end
  return false
end)

and this one too

someEntity:SetCustomCollisionCheck( true )
someEntity:CollisionRulesChanged()
local ncProp = {} -- Just a table of random props
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
  if not ncProp[ent1] and not ncProp[ent2] then return end
  return false
end)

Crashes the server

someEntity:SetCustomCollisionCheck( true )
local ncProp = {} -- Just a table of random props
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
  if not ncProp[ent1] and not ncProp[ent2] then return end
  ent1:CollisionRulesChanged()
  return false
end)

This one too crashes the server...

someEntity:SetCustomCollisionCheck( true )
local ncProp = {} -- Just a table of random props
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
  if not ncProp[ent1] and not ncProp[ent2] then return end
  ent1:CollisionRulesChanged()
  ent2:CollisionRulesChanged()
  return false
end)

[zamboni]

flip-flopping collision rules for an entity is bad practice.

The ShouldCollide hook is generally intended for unchanging collision rules, such as "entities of type A will never collide with type B" — not "entities of type A will sometimes collide with type B."

EDIT:

I have also heard that changing collision rules between two entities while they are colliding/penetrating will also break the physics.
Even more, someone long ago said they had issues with altering collisions between entities of the same class.

[Mechanical Mind]

someEntity = Entity(1):GetEyeTrace().Entity

someEntity:SetCustomCollisionCheck( true )
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
    if ent1 == game.GetWorld() || ent2 == game.GetWorld() then return end
    if ent1.ShouldCollideTest || ent2.ShouldCollideTest then
        return false
    end
end)

timer.Create("Test", 1, 0, function ()
    someEntity.ShouldCollideTest = !someEntity.ShouldCollideTest
    someEntity:CollisionRulesChanged()
end)

CollisionRulesChanged should be called after you change the conditions when it should collide, not in the shouldcollide hook. I assume breaking the physics was stuff falling through the floor. The world counts as an entity, so you removed collisions with the world.

[edgarasf123]

[QUOTE=Mechanical Mind;50815170]

someEntity = Entity(1):GetEyeTrace().Entity

someEntity:SetCustomCollisionCheck( true )
hook.Add("ShouldCollide", "Test", function(ent1, ent2)
	if ent1 == game.GetWorld() || ent2 == game.GetWorld() then return end
	if ent1.ShouldCollideTest || ent2.ShouldCollideTest then
		return false
	end
end)

timer.Create("Test", 1, 0, function ()
	someEntity.ShouldCollideTest = !someEntity.ShouldCollideTest
	someEntity:CollisionRulesChanged()
end)

CollisionRulesChanged should be called after you change the conditions when it should collide, not in the shouldcollide hook.[/QUOTE]

Oh, I see. But what if I the code doesn't know whether it will return true or false prior ShouldCollide hook? Or am I supposed to loop trough all entities to get those conditions?

[Mechanical Mind]

You should do something similar to what I've done, inside another hook (e.g. think), when you want to change whether an entity should collide, set a variable on the entity and call CollisionRulesChanged.
Then the should collide hook would decide based upon the variable you set, as in my example.

Also given that ShouldCollide can break the game, I would keep the logic inside of it simple so there's less chance of a bug causing problems in uncommon situations.

[edgarasf123]

[QUOTE=Mechanical Mind;50815212]You should do something similar to what I've done, inside another hook (e.g. think), when you want to change whether an entity should collide, set a variable on the entity and call CollisionRulesChanged.
Then the should collide hook would decide based upon the variable you set, as in my example.

Also given that ShouldCollide can break the game, I would keep the logic inside of it simple so there's less chance of a bug causing problems in uncommon situations.[/QUOTE]

The documentation says "Prior returning false, call ENT:CollisionRulesChanged()". Can ENT:CollisionRulesChanged() be called for other than returning false? Like returning nil or true?

[Phoenixf129]

[QUOTE=edgarasf123;50815236]The documentation says "Prior returning false, call ENT:CollisionRulesChanged()". Can ENT:CollisionRulesChanged() be called for other than returning false? Like returning nil or true?[/QUOTE]

Call it whenever the Collision Rules have changed.