Removing falling object with onBeginContact

Dikkesnoek · April 2013

Hi,

I don't know how to fix this. I have several object falling from the sky. If I use a
sprite:getY() in the onEnterFrame() handler I can remove one the objects. When
I create a body on the bottom and use the onBeginContact() handler it will react
weird. I think that it has something to do that I could'nt determine the exact
sprite which is contacting the bottomBody. If I pick a object that has been created
later (I create the objects with a timer) and I throw it down (it will pass an other
object) than it will not be destroyed. Here is a piece of code:

 
local bottomBody = world:createBody({type = b2.STATIC_BODY})
local bottomShape = b2.CircleShape.new(480, 670, 220)
bottomBody:createFixture{shape = bottomShape, density = 0}
bottomBody.name = "bottomBody"
 
function onEnterFrame(event)
	world:step(1/60, 8, 3)
 
	for body,sprite in pairs(actors) do
		sprite:setPosition(body:getPosition())
		sprite:setRotation(body:getAngle() * 180 / math.pi)		
 
		--if sprite:getY() > 340 then  -- THIS WORKS --
		if (removeObject) then         -- THIS NOT --
			world:destroyBody(body)
			stage:removeChild(sprite)
			actors[body] = nil
			removeObject = false
		end
	end
end
 
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()
 
	if ((bodyA.name == "bottomBody")  and (bodyB.name == "fallingBody") or 
	    (bodyA.name == "fallingBody") and (bodyB.name == "bottomBody")) then
 
		score = score + 1
		scoreText:setText(score)
 
		removeObject = true
	end
end

If you'll try to remove the specific falling object in the onBeginContact() handler
it will remove all the sprites.

Thanks,

Marc

Dikkesnoek · April 2013

Is there a way to detect the x and y positions of the collisions?
event.x and event.y will not work in the onBeginContact(event)
handler.

Regards,

Marc

ar2rsawseen · April 2013

@Dikkesnoek to destroy bodies, you can create another queue like this:
http://www.giderosmobile.com/forum/discussion/comment/5908#Comment_5908

There is a way to get collision coordinates, check this thread:
http://www.giderosmobile.com/forum/discussion/comment/22493#Comment_22493

But what I would recommend is to set up the sensors, where your body's might land, etc, so everytime you get a collision with your hidden sensor, you know body should be removed

Dikkesnoek · April 2013

Thanks ar2rsawseen. This is a nice solution. I've seen the locked
message a lot. I did the following by the way:

function onEnterFrame(event)
	world:step(1/60, 8, 3)
 
	for body,sprite in pairs(actors) do
		sprite:setPosition(body:getPosition())
		sprite:setRotation(body:getAngle() * 180 / math.pi)		
 
		if (sprite.removeMe) then
			world:destroyBody(body)
			stage:removeChild(sprite)
			actors[body] = nil
 
			sprite.removeMe = false
			sun:setRotation(sun:getRotation() - 30)
		end
	end
end
 
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()
 
	if ((bodyA.name == "bottomBody")  and (bodyB.name == "fallingBody") or 
	    (bodyA.name == "fallingBody") and (bodyB.name == "bottomBody")) then
 
		if  (bodyA.name == "fallingBody") then
			for body,sprite in pairs(actors) do
				if (body == bodyA) then
					sprite.removeMe = true
				end
			end
		end
		if  (bodyB.name == "fallingBody") then
			for bodyB,sprite in pairs(actors) do
				if (body == bodyB) then
					sprite.removeMe = true
				end
			end
		end
 
		score = score + 1
		scoreText:setText(score)
 
		print("COLLISION: ", score)
	end
end

This works too.

Regards,

Marc

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