Detect collision of kinematic bodies

ar2rsawseen

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.

atilim

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

ar2rsawseen

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

jarosmartin

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)

ar2rsawseen

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)

jarosmartin

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)

ar2rsawseen

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

jarosmartin

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)