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dynamic change of body type (b2.DYNAMIC_BODY to b2.KINEMATIC_BODY and reverse) — Gideros Forum
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    dynamic change of body type (b2.DYNAMIC_BODY to b2.KINEMATIC_BODY and reverse)

    linker_ualinker_ua Member
    edited November 2011 in General questions
    Hi, is it possible to change type of phisical body in function onEnterFrame()

    For example I want to stick 2 objects like at this preview:
    http://www.freeimagehosting.net/d149f

    I detect collision but don't know how to stick it...
    Have you any ideas how to solve this solution?
    Tagged:
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    Comments

    • linker_ualinker_ua Member
      http://www.freeimagehosting.net/newuploads/d149f.gif
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    • atilimatilim Maintainer
      hi,

      You need to create weld joint to stick them together.
      http://en.wikipedia.org/wiki/Cytorus
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    • linker_ualinker_ua Member
      Thanks! I found it in reference manual! :) Hope that I will understand it...
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    • atilimatilim Maintainer
      :) weld joint is one of the easiest joints to use :)
      http://en.wikipedia.org/wiki/Cytorus
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    • linker_ualinker_ua Member
      edited December 2011
      Kinematic Object - barriers[1].body
      Dynamic Object - actors[1].body

      Creation weld joint on collision enter:
      jd = b2.createWeldJointDef(barriers[1].body, actors[1].body, barriers[1].body:getPosition(), actors[1].body:getPosition())
weldJoint = world:createJoint(jd)
      It give's me fatal error!

      Expression IsLocked == false

      When I use this code "onButtonPress" - than it works, else - fatal error..
      Works not so well! help to find my error
      -------------------------------------------------------- this don't works
local function onBeginContact(event)
	local fixtureA = event.fixtureA
	local fixtureB = event.fixtureB
	local bodyA = fixtureA:getBody()
	local bodyB = fixtureB:getBody()
	objectA = bodyA.name
	objectB = bodyB.name
	if (objectB == "Barrier") or (objectA == "Barrier") then
	jd = b2.createWeldJointDef(barriers[1].body, actors[1].body, barriers[1].body:getPosition(), actors[1].body:getPosition())
		weldJoint = world:createJoint(jd)
	end
 
end
world:addEventListener(Event.BEGIN_CONTACT, onBeginContact)
--------------------------------------------------------this works
function onClick(event)
	if event:getTarget() == rightright then
		jd = b2.createWeldJointDef(barriers[1].body, actors[1].body, barriers[1].body:getPosition(), actors[1].body:getPosition())
		weldJoint = world:createJoint(jd)
	end
end
rightright:addEventListener("click", onClick)
----------------------------------------
      Thanks a lot! :)
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    • atilimatilim Maintainer
      edited December 2011
      Hi,

      Box2d locks the world while it dispatches events BEGIN_CONTACT, END_CONTACT, PRE_SOLVE and POST_SOLVE. And if the world is locked, these functions give assertion:

      b2.World:createBody
      b2.World:destroyBody
      b2.World:createJoint
      b2.World:destroyJoint
      b2.Body:createFixture
      b2.Body:destroyFixture
      b2.Body:setActive
      b2.Body:setPosition

      For your case, the solution is to create your joint outside of these events. (For example, you can set a flag and check this flag on ENTER_FRAME and if it's true create your joint)
      http://en.wikipedia.org/wiki/Cytorus
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    • linker_ualinker_ua Member
      edited December 2011
      do you mean something like this?
      r1 = 50 --radius of first body
r2 = 94 --radius of second body
 
local function onEnterFrame()
	world:step(1/60, 8, 3)
	local x1,y1 = actors[1].body:getPosition()
	local x2,y2 = barriers[1].body:getPosition()
	local length = math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2))
	print(length)
	if (length < (r1+ r2 + 20) and length > (r1+ r2)) and weldJoint == nil then
		jd = b2.createWeldJointDef(barriers[1].body, actors[1].body, barriers[1].body:getPosition(), actors[1].body:getPosition())
		weldJoint = world:createJoint(jd)
	end
end
      But if FPS drop, one frame when length value will be higher than (r1+ r2 + 20), next frame - after some seconds, then we could lost value when length < (r1+ r2 + 20).
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    • atilimatilim Maintainer
      edited December 2011
      Not exactly.

      I mean set a flag on onBeginContact function and test this flag on onEnterFrame, if true create your weld joint.
      local function onBeginContact(event)
  local fixtureA = event.fixtureA
  local fixtureB = event.fixtureB
  local bodyA = fixtureA:getBody()
  local bodyB = fixtureB:getBody()
  local objectA = bodyA.name
  local objectB = bodyB.name
  if (objectB == "Barrier") or (objectA == "Barrier") then
    createWeldJoint = true
  end
end
world:addEventListener(Event.BEGIN_CONTACT, onBeginContact)
 
local function onEnterFrame()
  if createWeldJoint == true then
    local jd = b2.createWeldJointDef(barriers[1].body, actors[1].body, barriers[1].body:getPosition(), actors[1].body:getPosition())
    weldJoint = world:createJoint(jd)
    createWeldJoint = false
  end
end
stage:addEventListener(Event.ENTER_FRAME, onEnterFrame)
      http://en.wikipedia.org/wiki/Cytorus
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    • linker_ualinker_ua Member
      ok thanks
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    • atilimatilim Maintainer
      np :)
      http://en.wikipedia.org/wiki/Cytorus
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