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    Detect collision of kinematic bodies

    ar2rsawseenar2rsawseen Maintainer
    edited February 2012 in General questions
    Is it possible?

    If there are two kinematic bodies draggable by user, and they shouldn't be overlapping (or atleast detect if they're overlapping).

    I know by default that kinematic and static bodies ar colliding (dispatching collision event) only with dynamic bodies, but in this case I don't need dynamic body, because gravity is applied, and I need that body to stay in position where user put it.

    Any interesting ideas are welcomed. ;)

    Likes: sslivka

    Dislikes: red032, talis, r033rt

    http://appcodingeasy.com/Gideros-Mobile
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    Comments

    • atilimatilim Maintainer
      edited February 2012
      maybe welding a dynamic body to your kinematic just for dispatching collision events? (I know it's a weird way :-B)

      Likes: duke2017

      http://en.wikipedia.org/wiki/Cytorus
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    • ar2rsawseenar2rsawseen Maintainer
      Well actually that is awesome idea.

      Was experimenting with switching bodies from kinematic to dynamic on dragging, which was a bad idea.

      Weding should be relatively easier. Thanks
      http://appcodingeasy.com/Gideros-Mobile
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    • jarosmartinjarosmartin Member
      Something like this ? The joint does not work on the code below
      circle = Bitmap.new(Texture.new("1.png"))
 
local actors = {}
local world = b2.World.new(0, 9)
local bodyDef1 = {type = b2.DYNAMIC_BODY, position = {x = 260, y = 210},  fixedRotation = true, linearDamping = 1}
local body1 = world:createBody(bodyDef1)
local shape1 = b2.PolygonShape.new()
shape1:setAsBox(50, 50)
body1:createFixture{shape = shape1, density = 1}
body1.name="circle1"
 
stage:addChild(circles[1])
actors[body1] =  circles[1]
 
local bodyDef2 = {type = b2.STATIC_BODY, position = {x = 260, y = 210}, fixedRotation = true, linearDamping = 1}
local body2 = world:createBody(bodyDef2)
 
local jointDef = b2.createWeldJointDef(body1,body2,0,0,0,0)
weldJoint = world:createJoint(jointDef)
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    • ar2rsawseenar2rsawseen Maintainer
      Hello @jarosmartin
      actually found a much better way, simply do not use sensors if you need collisions. Use collision filters instead:
      http://www.giderosmobile.com/DevCenter/index.php/Forum_FAQ#How_can_I_use_collision_filters.3F

      But if you are interested in Welding joints, then you should use common point of both bodies, in your case their center (260,210) coordinates, like this:
      local jointDef = b2.createWeldJointDef(body1, body2, 260, 210, 260, 210)
weldJoint = world:createJoint(jointDef)


      http://appcodingeasy.com/Gideros-Mobile
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    • jarosmartinjarosmartin Member
      edited July 2012
      Hello @ar2rsawseen and thanks for the update !. I think my problem is the "multitouch.lua" from the touch Explorer example. I've attached the class. It returns index, position X, position Y. It seems the bodies' positions never get updated. If position[2] position[3] are assigned to bodies inside onEnterFrame then there is a weird behavior (the circle starts rotating around the finger).
       
--WeldJoint Example
require "box2d"
b2.setScale(20)
 
local circle = Multitouch.new("1.png",1)
 
local actors = {}
local world = b2.World.new(0, 3)
 
local body1 = world:createBody{type = b2.STATIC_BODY, position = {x = 280, y = 410}}
local circleFilter = {categoryBits = 2, maskBits = 1}
body1.name="circle"
local circleShape = b2.PolygonShape.new()
circleShape:setAsBox(50, 50)
local fixture1 = body1:createFixture{shape = circleShape, density = 1.0, friction = 0.1, restitution = 0.8, filter = circleFilter}
 
stage:addChild(circle)
actors[body1] = circle
 
-------------------------------box-------------------------------
local box = Bitmap.new(Texture.new("box.png"))
box:setX(300)
box:setY(600)
box:setAnchorPoint(0.5,0.5)
stage:addChild(box)
local boxShape = b2.PolygonShape.new()
boxShape:setAsBox(40,40)
local body3 = world:createBody{type = b2.STATIC_BODY, position = {x=300, y=600}}
local boxFilter = {categoryBits = 1, maskBits = 2}
body3.name="box"
fixture2 = body3:createFixture{shape = boxShape, density = 0, filter = boxFilter}
 
local function onBeginContact(event)
	-- you can get the fixtures and bodies in this contact like:
	local fixtureA = event.fixtureA
	local fixtureB = event.fixtureB
	local bodyA = fixtureA:getBody()
	local bodyB = fixtureB:getBody()
 
	print(bodyA.name.."INSIDE"..bodyB.name)
end
 
local function onEndContact(event)
	-- you can get the fixtures and bodies in this contact like:
	local fixtureA = event.fixtureA
	local fixtureB = event.fixtureB
	local bodyA = fixtureA:getBody()
	local bodyB = fixtureB:getBody()
 
	print(bodyA.name.."OUTSIDE"..bodyB.name)
end
 
world:addEventListener(Event.BEGIN_CONTACT, onBeginContact)
world:addEventListener(Event.END_CONTACT, onEndContact)
 
-- step the world and then update the position and rotation of sprites
 
local function onEnterFrame()
--Do something to update postion of body1
	world:step(1/60, 8, 3)
	for body,sprite in pairs(actors) do
		sprite:setPosition(body:getPosition())
		sprite:setRotation(body:getAngle() * 180 / math.pi)
	end
end
 
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)
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    • ar2rsawseenar2rsawseen Maintainer
      You can't drag physical bodies as shown in multitouch explorer, that would feel unnatural and is against how box2d works. You need to use mousejoint for that purpose:

      http://appcodingeasy.com/Gideros-Mobile/Dragging-Box2d-object-in-Gideros-Mobile
      http://appcodingeasy.com/Gideros-Mobile
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    • jarosmartinjarosmartin Member
      Like this. Great !
      --MouseJoint Example
require "box2d"
b2.setScale(20)
local actors = {}
local world = b2.World.new(0, 0)
local ground = world:createBody({})
local bodyDef = {type = b2.DYNAMIC_BODY, position = {x = 160, y = 110}, fixedRotation = true, linearDamping = 1}
local body = world:createBody(bodyDef)
body:setLinearDamping(100)
body:setAngularVelocity(0)
local shape = b2.PolygonShape.new()
shape:setAsBox(25, 25)
local fixture = body:createFixture{shape = shape, density = 1, restitution=0, friction=1}
body.name = "circle"
 
local sprite = Bitmap.new(Texture.new("1.png", true))
sprite:setAnchorPoint(0.5, 0.5)
stage:addChild(sprite)
 
actors[body] = sprite
 
-------------------------------box-------------------------------
local box = Bitmap.new(Texture.new("box.png"))
box:setX(300)
box:setY(600)
box:setAnchorPoint(0.5,0.5)
stage:addChild(box)
local boxShape = b2.PolygonShape.new()
boxShape:setAsBox(40,40)
local body3 = world:createBody{type = b2.STATIC_BODY, position = {x=300, y=600}}
 
body3.name="box"
fixture2 = body3:createFixture{shape = boxShape, density = 0, isSensor=true}
 
local function onBeginContact(event)
	-- you can get the fixtures and bodies in this contact like:
	local fixtureA = event.fixtureA
	local fixtureB = event.fixtureB
	local bodyA = fixtureA:getBody()
	local bodyB = fixtureB:getBody()
 
	print(bodyA.name.."INSIDE"..bodyB.name)
end
 
local function onEndContact(event)
	-- you can get the fixtures and bodies in this contact like:
	local fixtureA = event.fixtureA
	local fixtureB = event.fixtureB
	local bodyA = fixtureA:getBody()
	local bodyB = fixtureB:getBody()
 
	print(bodyA.name.."OUTSIDE"..bodyB.name)
end
 
world:addEventListener(Event.BEGIN_CONTACT, onBeginContact)
world:addEventListener(Event.END_CONTACT, onEndContact)
 
-- step the world and then update the position and rotation of sprites
local mouseJoint = nil
 
-- create a mouse joint on mouse down
function sprite:onMouseDown(event)
	if self:hitTestPoint(event.x, event.y) then
		local jointDef = b2.createMouseJointDef(ground, body, event.x, event.y, 100000,100)
		mouseJoint = world:createJoint(jointDef)
	end
end
 
-- update the target of mouse joint on mouse move
function sprite:onMouseMove(event)
	if mouseJoint ~= nil then
		mouseJoint:setTarget(event.x, event.y)
	end
end
 
-- destroy the mouse joint on mouse update up
function sprite:onMouseUp(event)
 
	if mouseJoint ~= nil then
		world:destroyJoint(mouseJoint)
		mouseJoint = nil
	end
end
 
-- register for mouse events
sprite:addEventListener(Event.MOUSE_DOWN, sprite.onMouseDown, sprite)
sprite:addEventListener(Event.MOUSE_MOVE, sprite.onMouseMove, sprite)
sprite:addEventListener(Event.MOUSE_UP, sprite.onMouseUp, sprite)
 
local function onEnterFrame()
	world:step(1/60, 8, 3)
 
	for body,sprite in pairs(actors) do
		sprite:setPosition(body:getPosition())
		sprite:setRotation(body:getAngle() * 180 / math.pi)
	end
end
 
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)
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