Destroy an Object

Monkey Forums/Monkey Beginners/Destroy an Object

Moerin

(Posted 2014) [#1]

Hi,

I try to code a game with a bouncy ball and an use of Box2D port for monkey.

I try to operate a reset feature to set my object at his original position.
So i have thought to delete my object and recreate it. Since Monkey have a garbage collector, i thought to set my object to the NULL value and recall the new operator on it.

The problem is that my previous object is still here with my new object.

How i manage it.

Method StarGame:Void()
	'	_aObstacleList.Clear()
		
		' Set the object to destroy it
		_ballObject = Null
		
		' Creation or Recreation
		_ballObject = New Ball(SCREEN_WIDTH2, 10, 1, pxToM, _b2World, _gfxWheelImage)
		_ballObject._b2BallBody.SetLinearVelocity(New b2Vec2(0, 20))
		
	'	CreateObstacle()
		
	End Method

Here's my full code :

Import gameClasses

Global gameScreen:GameScreen

Class Game Extends DiddyApp
	Method Create:Void()
		gameScreen = New GameScreen
		gameScreen.PreStart()
		Seed = RealMillisecs()
	End Method
	
End Class

Class GameScreen Extends Screen
	Field _bDebug:bool = False
	
	Field _ballObject:Ball
	
	Field startingVelocity:b2Vec2 ' Velocity for movement
	
	Field _fWorldScale:Float = 20
	Field mToPx:float
	Field pxToM:float
	
	Field _b2Gravity:b2Vec2 ' Gravity creation
	Field _b2World:b2World ' Physical world creation
	
	Field _contactListener:ContactListener
	
	Field _gfxWheelImage:Image = New Image()
	Field _gfxObslImage:Image = New Image()
	Field _lgfxWheelImage:List<Image> = New List<Image>()
	
	Field _aWheelList:List<b2Body> = New List<b2Body>()
	Field _aObstacleList:List<Peg> = New List<Peg>()
	
	Method New()
		name = "Game"
	End Method
	
	Method Start:Void()
		mToPx = _fWorldScale ' pixel / meter
		pxToM = 1 / mToPx
		
		_gfxWheelImage = LoadImage("SimpleWheel3.png", 1, Image.MidHandle)
		'_gfxObsImage = LoadImage("", 1, Image.MidHandle)
		
		_b2Gravity = New b2Vec2(0, 10) ' world gravity
		_b2World = New b2World(_b2Gravity, True) ' Second parament set object in sleep mode for performance gain
		
		 '// set debug draw
		Local dbgDraw:b2DebugDraw = New b2DebugDraw()
        dbgDraw.SetDrawScale(20.0)
        dbgDraw.SetFillAlpha(0.3)
        dbgDraw.SetLineThickness(1.0)
        dbgDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit)'| b2DebugDraw.e_pairBit)
        _b2World.SetDebugDraw(dbgDraw)
		
		StarGame()
		
		CreateBoundaries() ' ground + left and right wall
		
	End Method
	
	Method StarGame:Void()
	'	_aObstacleList.Clear()
		
		' Set the object to destroy it
		_ballObject = Null
		
		' Creation or Recreation
		_ballObject = New Ball(SCREEN_WIDTH2, 10, 1, pxToM, _b2World, _gfxWheelImage)
		_ballObject._b2BallBody.SetLinearVelocity(New b2Vec2(0, 20))
		
	'	CreateObstacle()
		
	End Method
	
	Method Update:Void()
	
		If KeyHit(KEY_R) Then
			StarGame()
		ElseIf KeyHit(KEY_D) Then
			If _bDebug Then
				_bDebug = False
			Else
				_bDebug = True
			EndIf
		ElseIf KeyHit(KEY_S)
			
		EndIf
		
'		If _ballObject._bDestroy Then
'			_ballObject = Null
'		EndIf

	'	Print _b2WheelBody.GetPosition().x + " " + _b2WheelBody.GetPosition().y
	
		_b2World.TimeStep(0.025, 10, 10) ' remplacement de la methode Step Take a time step. This performs collision detection, integration, and constraint solution.
		_b2World.ClearForces() ' To Call after each step else create some sub-steps which impact performance
		
	'	Print _b2WheelBody.GetPosition().x + " " + _b2WheelBody.GetPosition().y
	End Method
	
	Method Render:Void()
		Cls
		
		If _bDebug Then
			' Render debug
			_b2World.DrawDebugData()
		Else
			If _ballObject._bDestroy = False Then
				_ballObject.Render()
			EndIf
		
			RenderObstacle()
		
			'DrawImage(_gfxWheelImage, SCREEN_WIDTH2, SCREEN_HEIGHT2)
		
		EndIf
		
		FPSCounter.Draw(0, 0)

	End Method
	
	Method CreateBoundaries:Void()
			' Ground
		Local b2GroundBodyDef:b2BodyDef
		Local b2GroundBody:b2Body
		Local b2GroundShape:b2PolygonShape
		Local b2GroundFixtureDef:b2FixtureDef
		Local b2GroundFixture:b2Fixture
		
		' Right Wall
		Local b2RightBodyDef:b2BodyDef
		Local b2RightBody:b2Body
		Local b2RightShape:b2PolygonShape
		Local b2RightFixtureDef:b2FixtureDef
		Local b2RightFixture:b2Fixture
		
		' Left Wall
		Local b2LeftBodyDef:b2BodyDef
		Local b2LeftBody:b2Body
		Local b2LeftShape:b2PolygonShape
		Local b2LeftFixtureDef:b2FixtureDef
		Local b2LeftFixture:b2Fixture
		
		' Init Ground *object are static by default*
		b2GroundBodyDef = New b2BodyDef()
		b2GroundBodyDef.position.Set(0, SCREEN_HEIGHT * pxToM) ' set before CreateBody method or the change 'll be ignore
		b2GroundBody = _b2World.CreateBody(b2GroundBodyDef)
		b2GroundShape = New b2PolygonShape()
		b2GroundShape.SetAsBox(SCREEN_WIDTH, 1)
		b2GroundFixtureDef = New b2FixtureDef()
		b2GroundFixtureDef.shape = b2GroundShape
		b2GroundFixture = b2GroundBody.CreateFixture(b2GroundFixtureDef)
		
		' Init Left wall *object are static by default*
		b2LeftBodyDef = New b2BodyDef()
		b2LeftBodyDef.position.Set(0, 0) ' set before CreateBody method or the change 'll be ignore
		b2LeftBody = _b2World.CreateBody(b2LeftBodyDef)
		b2LeftShape = New b2PolygonShape()
		b2LeftShape.SetAsBox(1 * pxToM, SCREEN_HEIGHT * pxToM)
		b2LeftFixtureDef = New b2FixtureDef()
		b2LeftFixtureDef.shape = b2LeftShape
		b2LeftFixture = b2LeftBody.CreateFixture(b2LeftFixtureDef)
		
		' Init Right wall *object are static by default*
		b2RightBodyDef = New b2BodyDef()
		b2RightBodyDef.position.Set(SCREEN_WIDTH * pxToM, 0) ' set before CreateBody method or the change 'll be ignore
		b2RightBody = _b2World.CreateBody(b2RightBodyDef)
		b2RightShape = New b2PolygonShape()
		b2RightShape.SetAsBox(1, SCREEN_HEIGHT)
		b2RightFixtureDef = New b2FixtureDef()
		b2RightFixtureDef.shape = b2RightShape
		b2RightFixture = b2RightBody.CreateFixture(b2RightFixtureDef)
	End Method
	
	Method CreateObstacle:Void() ' watch out for the size Box2D use meters not pixel.
		For Local i:= 1 To 9
			For Local j:= 1 To 5
			Local pegObject:Peg = New Peg(i * 60, j * 60, 0.5, _fWorldScale, _b2World, _gfxObslImage)
				_aObstacleList.AddLast(pegObject)
				_contactListener = New ContactListener(pegObject)
				_b2World.SetContactListener(_contactListener)
			Next
		Next
		
	End Method
	
	Method RenderObstacle:Void()
		For Local obs:Peg = EachIn _aObstacleList
'			obs.Render()
		Next
	End Method
	
	Method PushWheel:Void()
		For Local wheel:b2Body = EachIn _aWheelList
			If IsInCircle(diddyGame.mouseX, diddyGame.mouseY, wheel.GetPosition().x * mToPx, wheel.GetPosition().y * mToPx, wheel.GetFixtureList().GetShape().m_radius * mToPx) and MouseHit() Then
				If (wheel.GetPosition().x * mToPx - diddyGame.mouseX) > 0 And (wheel.GetPosition().y * mToPx - diddyGame.mouseY) > 0 Then
					wheel.ApplyImpulse(New b2Vec2(50 * mToPx, 50 * mToPx), wheel.GetPosition())
				ElseIf(wheel.GetPosition().x * mToPx - diddyGame.mouseX) < 0 And (wheel.GetPosition().y * mToPx - diddyGame.mouseY) > 0 Then
					wheel.ApplyImpulse(New b2Vec2(-50 * mToPx, 50 * mToPx), wheel.GetPosition())
				ElseIf(wheel.GetPosition().x * mToPx - diddyGame.mouseX) > 0 And (wheel.GetPosition().y * mToPx - diddyGame.mouseY) < 0 Then
					wheel.ApplyImpulse(New b2Vec2(50 * mToPx, -50 * mToPx), wheel.GetPosition())
				ElseIf(wheel.GetPosition().x * mToPx - diddyGame.mouseX) < 0 And (wheel.GetPosition().y * mToPx - diddyGame.mouseY) < 0 Then
					wheel.ApplyImpulse(New b2Vec2(-50 * mToPx, -50 * mToPx), wheel.GetPosition())
				EndIf
			EndIf
		Next
	End Method
	
	Method IsInCircle:Bool(mX:float, mY:Float, cX:Float, cY:Float, radius:Float)
		If Sqrt( ( (mX - cX) * (mX - cX)) + ( (mY - cY) * (mY - cY))) < radius Then
			Return True
		Else
			Return False
		EndIf
		
	End Method

End Class

dawlane

(Posted 2014) [#2]

The Garbage collector only gets call at specific times. Though you have NULLed an object, it still exists until the GC is called. If it's only the one object why delete it and try to create a new one when it's more efficient just to re-use the object by resetting it's values.

Moerin

(Posted 2014) [#3]

Because i don't figure out how to reset an object value create with box2D. I have rode that the regular way is to detroy your object, i can do that with c++ and Java but not with Monkey.

MikeHart

(Posted 2014) [#4]

Just store a NULL inside that field where you stored the bodx2D object in and it will be collected.

EDIT: Ah, I saw you use diddy and I didn't study your code troughly. Could be that diddy holds the box2D object somewhere too.

Moerin

(Posted 2014) [#5]

Yeah, i have forgot to mention that i'm using diddy. Ok, but i'm at the begining of my project. Do you think if i change my framework for fantom i'll be able to find an issue?

Gerry Quinn

(Posted 2014) [#6]

Something else remembers that object too and is still drawing it.

It makes no difference whether the garbage collector has been called yet or not, it only gets called for objects that *everything* has forgotten about.

If you could have deleted it like in C++, you'd probably get a crash instead when the other thing tried to use it. In a GC language, it just carries on existing.

Just go through your code and think about the life cycle of objects and what things get to know about them.

MikeHart

(Posted 2014) [#7]

@Moerin

I don't know if you will find an issue. If you are happy with Diddy, I see no reason to change it.

AdamRedwoods

(Posted 2014) [#8]

Monkey's port of Box2D does *NOT* collect objects. you must explicitly Destroy() them. monkey's port is based of the flash port, so you can use that documentation:
http://www.box2dflash.org/docs/2.0.2/manual#Memory_Management

_world.DestroyBody(_ballObject)

this is primarily because Monkey does not use implicit destructors.

MikeHart

(Posted 2014) [#9]

You are right Adam, forgot about that totally. I do the same in the box2D interface of fantomEngine.

Moerin

(Posted 2014) [#10]

It's work now. Thanks to each of you for your help.