How can i destroy all my scene objects on scene exit?

AxlFlame · August 2012

Hi,
I'm having this issue and i'm getting desperate about it...

I have a game where i create many blocks and make them go from right to left via parallax effect and between them there's space for the player to draw a bridge so the character would not fall. When they exit the screen i destroy the blocks and create the new one on the right side.
I also have a pause screen from where i can exit the game and return to the title screen. My problem is that whenever i exit the scene, the physical bodies of the blocks somehow stays on the stage, even though i'm not at the game scene anymore, that is causing the game to crash if i try to draw something over the body that is already there.

How can i destroy those remaining bodies? I managed to destroy the player's character one, but i can't seem to be able to reference the bodies from the bridge and the blocks....

I tried to upload my .lua files but the forum refuses to let me lol So i'm pasting them here...

Please, any help would be deeply appreciated.

AxlFlame · August 2012

Ok, so my code is too big and i can't post it either... so here goes a few parts...

This is the function that creates the blocks

newBlock = function()
	--this function includes all the "paths" logic.
	local block;
	--if the currentBlock needed is the first,
	--then we use a different image (headBlockIMG), decide the length of the new path,
	--decide it's distance from the previous one, and add a physics body that is as big as the whole path.
	if currentBlock == 1 then
		currentPathLen = mRandom(minPathLen, maxPathLen);
		dropEnemyAtBlock = mRandom(2, currentPathLen-1);
		block = newBitmap(BlocoIMG);
		block:setAnchorPoint(0.5, 0.5);
		sceneParent:addChild(block);
		if lastBlock then
			block:setPosition(lastBlock:getX()+mRandom(minDistWidth, maxDistWidth),
							  mMin(minHeight,mMax(maxHeight, lastBlock:getY()+mRandom(-minDistHeight, maxDistHeight))));
		else
			--let's set first block of the game position
			block:setPosition(block:getWidth()*0.5, 220);
		end
		block.body = b2World:createBody{type = b2STATIC_BODY, 
						position = {x = block:getX(), y = block:getY()},
					   };
		block.body.name = "block";
		block.body.sprite = block;
		local blockShape = b2PolygonShape.new();
		local blockWidth, blockHeight = block:getWidth(), block:getHeight();
		blockShape:set(-blockWidth*0.5, -blockHeight*0.5,
						-blockWidth*0.5+blockWidth*currentPathLen, -blockHeight*0.5,
						-blockWidth*0.5+blockWidth*currentPathLen, blockHeight*0.5,
						-blockWidth*0.5, blockHeight*0.5);
		block.body:createFixture{shape = blockShape,
							friction = 0,
							restitution = 0,
							density = 10,
							isSensor = false
						   };
		block.removeAt = block:getWidth()*currentPathLen;
		function block:onEnterFrame()
			self:setX(self:getX()-layer1Speed);
			self.body:setPosition(self:getPosition());
			if not self.created then
				if self:getX() < screenWidth then
					self.created = true;
					newBlock();
				end
			else
				if self:getX() < -block.removeAt then
					b2World:destroyBody(self.body);
					self.body = nil;
					self:removeEventListener(Event.ENTER_FRAME, self.onEnterFrame, self);
					sceneParent:removeChild(self);
				end
			end
		end
	elseif currentBlock == currentPathLen then
		--if the block is the last of the path, then we use a "endBlockIMG".
		currentBlock = 0;
		block = newBitmap(BlocoIMG);
		block:setAnchorPoint(0.5, 0.5);
		sceneParent:addChild(block);
		block:setPosition(lastBlock:getX()+block:getWidth(), lastBlock:getY());
		function block:onEnterFrame()
			self:setX(self:getX()-layer1Speed);
			if not self.created then
				if self:getX() < screenWidth then
					self.created = true;
					newBlock();
				end
			else
				if self:getX() < -50 then
					self:removeEventListener(Event.ENTER_FRAME, self.onEnterFrame, self);
					sceneParent:removeChild(self);
				end
			end
		end
	else
		block = newBitmap(BlocoIMG);
		block:setAnchorPoint(0.5, 0.5);
		sceneParent:addChild(block);
		block:setPosition(lastBlock:getX()+block:getWidth(), lastBlock:getY());
		function block:onEnterFrame()
			self:setX(self:getX()-layer1Speed);
			if not self.created then
				if self:getX() < screenWidth then
					self.created = true;
					newBlock();
				end
			else
				if self:getX() < -50 then
					self:removeEventListener(Event.ENTER_FRAME, self.onEnterFrame, self);
					sceneParent:removeChild(self);
				end
			end
		end
		--we only want monsters to drop on the "middle" blocks, so here we check if we must create one, and decide randomly which one.
		if currentBlock == dropEnemyAtBlock then
				dropEnemyAtBlock = 0;
				local enemyType = mRandom(1, #enemyTable);
				local enemy = enemyTable[enemyType](enemyTexture[enemyType], block:getX(), block:getY()-(block:getHeight()*0.5), b2World);
				sceneParent:addChild(enemy);
				enemy.moveMe = function(object)
				local selfX, selfY = object:getPosition();
				object:setPosition(selfX-layer1Speed, selfY);
				return b2World;
			end
			enemy:addListeners();
		end
	end
	function block:removeListeners()		
		block:removeEventListener(Event.ENTER_FRAME, block.onEnterFrame, block);
	end
	function block:addListeners()
		block:addEventListener(Event.ENTER_FRAME, block.onEnterFrame, block);
	end
	currentBlock = currentBlock+1;
	block:addEventListener(Event.ENTER_FRAME, block.onEnterFrame, block);
	lastBlock = block;
end

AxlFlame · August 2012

This is the init from my game scene, it includes the function i use to allow the gestures recognition with the help of the Gestures.lua file.

--on scene initialization
function bonecosDesenho:init()
 
	if sets.music then
		music.channel = music.minigamesDesenho:play(0,1000000)
	end	
 
	-- Resetando alguns valores
	lastBlock = nil;
	currentBlock = 1;
	currentScore = 0;
	--currentLifes = 3;
 
	enemyTable = {bDobstaculos.new,
				bDobstaculos.new};	
 
	--create world instance
	b2World = b2.World.new(0, 18, true)
	b2PolygonShape = b2.PolygonShape;
	b2STATIC_BODY = b2.STATIC_BODY;		
 
	_G.b2World = b2World;
	sceneParent = self;
	createParallaxBG();
	newBlock();	
	currentPathLen = 20;
 
	--Criando e guardando referência pro boneco
	self.boneco = self:boneco(100, 100)
 
	--Recreating first block body due to the manual change in pathLen
	b2World:destroyBody(lastBlock.body);	
	lastBlock.body = b2World:createBody{type = b2STATIC_BODY, 
										position = {x = lastBlock:getX(), y = lastBlock:getY()},
									   };
		local blockShape = b2PolygonShape.new();
		blockShape:set(-lastBlock:getWidth()*0.5, -lastBlock:getHeight()*0.5,
						-lastBlock:getWidth()*0.5+lastBlock:getWidth()*currentPathLen, -lastBlock:getHeight()*0.5,
						-lastBlock:getWidth()*0.5+lastBlock:getWidth()*currentPathLen, lastBlock:getHeight()*0.5,
						-lastBlock:getWidth()*0.5, lastBlock:getHeight()*0.5);
		lastBlock.body:createFixture{shape = blockShape,
							friction = 0,
							restitution = 0,
							density = 10,
							isSensor = false
						   };
	lastBlock.removeAt = lastBlock:getWidth()*currentPathLen;
	lastBlock.body.name = "block";
	lastBlock.body.sprite = lastBlock;
	dropEnemyAtBlock = 0;	
 
	--set up debug drawing
	--[[local debugDraw = b2.DebugDraw.new()
	self.world:setDebugDraw(debugDraw)
	self:addChild(debugDraw)--]]
 
	--Adding the score
	objScore = GCscore.new({Texture.new("images/0.png"), Texture.new("images/1.png"), Texture.new("images/2.png"),
							Texture.new("images/3.png"), Texture.new("images/4.png"), Texture.new("images/5.png"),
							Texture.new("images/6.png"), Texture.new("images/7.png"), Texture.new("images/8.png"), 
							Texture.new("images/9.png")},
							25);
	self:addChild(objScore);
	objScore:setX(screenWidth-30);
	objScore:setScore(100);
	objScore:setScore(20);
 
	--adding the pause button
	local pauseButton = GCpauseBut.new(newTexture("Buttons/PauseSmall.png"));
	self:addChild(pauseButton);
	pauseButton:setPosition(screenWidth*0.01, 4);	
 
--===================================================
--				     GESTOS
--===================================================
 
--Shape para servir de scopo do verificador de gestos
local areaGestos = Shape.new()
		areaGestos:setFillStyle(Shape.SOLID, 0xC0C0C0, 0.5)   
		areaGestos:beginPath(Shape.NON_ZERO)
		areaGestos:moveTo(0, 195)
		areaGestos:lineTo(application:getContentWidth(), 195)
		areaGestos:lineTo(application:getContentWidth(), 225)
		areaGestos:lineTo(0, 225)
		areaGestos:lineTo(0, 195)
		areaGestos:endPath()
		self:addChild(areaGestos)
 
local font = TTFont.new("Fontes/tahoma.ttf", 20)
 
local myText = TextField.new(font, "Result: ")
myText:setPosition(50,50)
self:addChild(myText)
 
self.gest = Gestures.new({
	debug = true,
	draw = true,
	drawColor = 0xff0000,
	drawWidth = 5,
	autoTrack = true,
	scope = areaGestos,
	allowRotation = true,
	inverseShape = true,
	points = 33
})
 
self.callback = function(name)
	local debugDraw = b2.DebugDraw.new()
	b2World:setDebugDraw(debugDraw)
	stage:addChild(debugDraw)
	myText:setText(name)
	--Update
	local xIni = self.gest.points[1].x;
	local xFim = self.gest.points[#self.gest.points].x;
	local yIni, yFim = 196, 225;
	--Apaga o ultimo shape para recriar
	bridge:clear()
	if bridge.body then
		b2World:destroyBody(bridge.body)
	end
	--Criando novo shape
	bridge:setFillStyle(Shape.SOLID, 00000000, 0.5) 
	bridge:beginPath(Shape.NON_ZERO)
	--calculate drawn width
	local width = self.gest.points[#self.gest.points].x - self.gest.points[1].x
	print(self.gest.points[#self.gest.points].x, self.gest.points[1].x)
	--drawing shape from 0 coordinates
	bridge:moveTo(0, yIni)
	bridge:lineTo(width, yIni)
	bridge:lineTo(width, yFim)
	bridge:lineTo(0, yFim)
	bridge:lineTo(0, yIni)
	bridge:endPath()
	areaGestos:addChild(bridge)
	--adding to expected position
	bridge:setX(self.gest.points[1].x)
	--if drawing from left to right
	if self.gest.points[1].x < self.gest.points[#self.gest.points].x then
		bridge.left2right = true
	else
		bridge.left2right = false
	end
 
	bridge:setY(yFim/yIni)
 
	--Criando corpo fisico p/ ponte
	bridge.body = b2World:createBody{type = b2STATIC_BODY, 
									position = {x = xFim/xIni, y = yFim-4},
									};
	bridge.body.name = "bridge";	
	local bridgeShape = b2.PolygonShape.new()
	local bridgeWidth = bridge:getWidth()
	local bridgeHeight = bridge:getHeight()
	bridgeShape:set(-bridgeWidth, -bridgeHeight,
					-bridgeWidth+bridgeWidth, -bridgeHeight,
					-bridgeWidth+bridgeWidth, bridgeHeight,
					-bridgeWidth, bridgeHeight);	
	bridge.body:createFixture{shape = bridgeShape,
						friction = 0,
						restitution = 0,
						density = 10,
						isSensor = false
						};	
	local teste = bridge:getX()
	print (teste)
	--you don't need to define same methods all the time
	--and certainly don't need to add onEnterFrame event on each callback
	--there will be multiple on Enter frame events
	if not bridge.onEnterFrame then
		--movendo o shape e o corpo
		function bridge:onEnterFrame()
			--calculate new bridge x
			local bridgeX = bridge:getX()-3
			--change bridge position
			bridge:setX(bridgeX)
			if bridge.left2right then
				bridgeX = bridgeX + bridge:getWidth()
			end
			--if bridge x has body
			if bridge.body then
				--set bodies position alongside with bridge
				local _, bodyY = bridge.body:getPosition()
				bridge.body:setPosition(bridgeX, bodyY)
			end
			if bridge:getX() < -480 then
				bridge:clear()
				bridge:removeListeners()
			end
		end
		function bridge:removeListeners()
			bridge:removeEventListener(Event.ENTER_FRAME, bridge.onEnterFrame, bridge);
		end
		function bridge:addListeners()
		bridge:addEventListener(Event.ENTER_FRAME, bridge.onEnterFrame, bridge);
		end	
		bridge:addEventListener(Event.ENTER_FRAME, bridge.onEnterFrame, bridge);
	end
end
 
self.gest:addGesture("Line", {
	{x = 0, y = 0},
	{x = 0, y = 100}
}, self.callback)
 
self.gest:addGesture("ZigZag", {
	{x = 0, y = 0},
	{x = 50, y = 87},
	{x = 100, y = 0},
	{x = 150, y = 87},
}, callback)
 
local x = 0
local y = -100
local circle = {}
local totalPoints = 72
local step = (math.pi*2)/totalPoints
 
for angle = 1, totalPoints do
	local newX = x*math.cos(angle*step)-y*math.sin(angle*step)
	local newY = y*math.cos(angle*step)+x*math.sin(angle*step)
	local point = {x = newX, y = newY}
	table.insert(circle, point)
end
 
self.gest:addGesture("Circle", circle, callback)
 
--===================================================
--				 FIM GESTOS
--===================================================
	--run world
	self:addListeners();
	self:addEventListener(Event.REMOVED_FROM_STAGE, self.removedFromStage, self);	
	self:addEventListener(Event.ENTER_FRAME, self.onEnterFrame, self)
	--remove event on exiting scene
	self:addEventListener("exitBegin", self.onExitBegin, self)
end

AxlFlame · August 2012

And finally this is the function i was able to use to destroy the character's body.

--removing event on exiting scene
function bonecosDesenho:onExitBegin()
	print("oi")
	b2World:destroyBody(self.boneco.body);
	sceneParent = nil;
	self:removeEventListener(Event.ENTER_FRAME, self.onEnterFrame, self)
end

john26 · August 2012

Can you show the code where you destroy the blocks and bridges? Your function bonecosDesenho:onExitBegin() looks fine. You need to do the same thing for the other objects...

AxlFlame · November 2012

So, i wasn't actually destroying the bridge body, but I added this to the onExitBegin and it worked.

function BonecosDesenho:onExitBegin()
	b2World:destroyBody(self.boneco.body);
	b2World:destroyBody(bridge.body);
	sceneParent = nil;
	self:removeEventListener(Event.ENTER_FRAME, self.onEnterFrame, self)
end

If I try to follow that line and use this:

b2World:destroyBody(block.body);

It gives me this error:
attempt to index global 'block' (a nil value)

Sorry for taking so long... any help would be deeply appreciated.

hgvyas123 · November 2012

It gives me this error:
attempt to index global 'block' (a nil value)

generally this error will come when you are trying to access object which is already removed or that is a local inside any function[and hence not accessible where you are trying to access] if you are sure that it is not removed then you might have declared it as local in any other function try to remove that local and make that global after this every thing should work fine

also in the case you want to delete everything onExitBegin use this

	for i=self:getNumChildren(),1,-1 do
		local sprite = self:getChildAt(i)	
		if sprite.body then
 
			world:destroyBody(sprite.body)
		end
sprite:removeFromParent()--usually it will not needed as scenemanager do this for you
	end

AxlFlame · November 2012

Ok, i'm sorry for the dumb question, but to make the variable global, I simply need to remove the 'local' before? Indeed the block is being created as local inside the NewBlock function.
Assuming its that, I got another error:

"attempt to perform arithmetic on field 'removeAt' (a nil value)"

removeAt is a property of block, and after I tried to change block to global aparrently it started to receive nil...
That block.removeAt is located inside the NewBlock function I pasted here, halfway, right before the block onEnterFrame.

Btw, thanks for the advice regarding destroying everything! It works perfectly... except for the block of course =/

AxlFlame · November 2012

So, I tried switching back block to local block as I noticed that the problem is not that the blocks aren't being destroyed, its the bridge that isn't... at least using your code for destroying everything on the scene.

That said I tried to use this to destroy the bridge:

b2World:destroyBody(bridge.body);

But when I try that, and go to start this game scene again it says:

Body is already destroyed.

And the error points to this part:

if bridge.body then
	b2World:destroyBody(bridge.body)
end

What I don't understand is why do I get this error, if the 'if' is exactly to avoid that?

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