[Box2D] Create a collectable object like coins without bouncing

jeromegsq

Hello,

I try to make a body collectable like a coin.
I use this :

function Game:collision(e) local fixtureA = e.fixtureA local fixtureB = e.fixtureB local bodyA = fixtureA:getBody() local bodyB = fixtureB:getBody()   if bodyA.type == "gasoil" and bodyB.type == "copter" then Timer.delayedCall(1, function() bodyA.class:removeFromParent() bodyA:setActive(false) end) end end

But when my helicopter touch the gasoil body, it bounce a little.
How to fix this ?

Thank

jeromegsq

Sorry for the double post, but i found the solution

I had to add : fixture:setSensor(true) to my gasoil body (bodyA).

tkhnoman

There are many approach for this, but i usually just do this

- Set filter for copter's main fixture so it won't collis with items
- Made another fixture for copter that collis with items, which isSensor

jeromegsq

@tkhnoman
Could you explain how to use filter and sensor please ? I try but i didn't understand.
Of course i took a look to the Manual

tkhnoman

When you creating a fixture :

fixturer = body:createFixture{ shape = shapeUsed, density = densityUsed, restitution = bounceUsed, friction = frictionUsed, filter = filterUsed, isSensor = true}

Explanation is here :
http://docs.giderosmobile.com/reference/physics/b2Body/createFixture

If you set isSensor to true, like in that example, then the body would not calculate collision(like bounce, and friction) with the others.
[NB: Just for if you advanced enough later on, it also won't calculate event.contact, which mean you can't know where exactly the x and y collision happened]


Filter explanation is like this:

local charFilter = {categoryBits = 0b00000001, maskBits = 0b00000001} local charItemFilter = {categoryBits = 0b00000001, maskBits = 0b00000010} local itemFilter = {categoryBits = 0b00000010, maskBits = 0b00000011}

categoryBits indicate "where" the object belong to, and maskBits indicate whoever it would contact with.

In this example if you apply it on filterUsed, then:
- fixture with charFilter will collis with char itself
- fixture with charItemFilter will collis with itemFilter
- fixture with itemFilter will collis with itself, and with charItemFilter

if you're got used with hex, you can use 0x0001 to 0xFFFF, because the maximum is 0xFFFF, which goes so long if turned as binary, )

There are also groupIndex for filter parameter, explanation here :
http://docs.giderosmobile.com/reference/physics/b2Fixture/setFilterData#b2.Fixture:setFilterData

jeromegsq

@tkhnoman Thank you very much !

ar2rsawseen

Here is also a great tutorial on this topic
http://giderosmobile.com/forum/discussion/1070/a-little-information-about-collision-filters#Item_1