Box2s - How to change scrolling body?

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Box2s - How to change scrolling body?

(9 posts) (3 voices)

Started 1 year ago by Jack Here
Latest reply from Jack Here

Tags:

bodies
Box2D

Jack Here
Member
Say I create my world in box2d, then create a Hero on screen as well. Something like this:
```
[self SetUpWorld:winSize];
[self addHero];
```
Where SetUpWorld creates a normal box2d world, and addHero adds a CCSprite, B2body, fixture, etc.

Then i run my tick like the following:
```
world->Step(dt, 10, 8);
	for(b2Body* b = world->GetBodyList();b;b=b->GetNext())
	{
		if(b->GetUserData()!=NULL)
		{
			CCSprite* sprite = (CCSprite*)b->GetUserData();
			sprite.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
			sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());

				[self Scroll:sprite.position];

		}
	}
```
This allows me to move my hero and scroll him. Now, say I move and scroll my hero to a point that I no longer need him and want to scroll a different hero. So I add another hero to my world with the same method ([self addHero];). However the problem is that box2d is still 'scrolling' with my original hero. Is there a way to change bodies? Or maybe iterate through the world to get the new hero?
Posted 1 year ago #
zangmobile
Member

Can you post the Scroll method please? I think you can just destroy the existing body but would like to see what you are doing in the scroll method.

Posted 1 year ago #

Jack Here
Member

Sure here is what im using for the scroll

-(void)Scroll:(CGPoint) pos
{
	CGSize winSize = [[CCDirector sharedDirector] winSize];

	int x = MAX(pos.x, winSize.width / 2);
    int y = MAX(pos.y, winSize.height / 2);

	x = MIN(x, (level.TileMapWidth)
			- winSize.width / 2);
    y = MIN(y, (level.TileMapHeight)
			- winSize.height/2);

	CGPoint actualPosition = ccp(x, y);

    CGPoint centerOfView = ccp(winSize.width/2, winSize.height/2);
    CGPoint viewPoint = ccpSub(centerOfView, actualPosition);

	self.position = viewPoint;
}

Posted 1 year ago #

zangmobile
Member

What you are doing right now is looping over the bodies and scrolling all of them. What I would do is keep a reference to the active hero that the scrolling is based on and update it with the new hero takes over. Remember you will need to pan the viewpoint from sprite to sprite so it looks natural. That way also you can take it out of the the all body loop. and save some processing power.

Also you will have to destroy the body of the first hero if you do not want him to be affected by the box2d world anymore.

Something like this:

world->Step(dt, 10, 8);
	for(b2Body* b = world->GetBodyList();b;b=b->GetNext())
	{
		if(b->GetUserData()!=NULL)
		{
			CCSprite* sprite = (CCSprite*)b->GetUserData();
			sprite.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
			sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
		}
	}

        [self Scroll];

-(void)Scroll
{
       CGPoint pos = self.activeSprite.position;
	CGSize winSize = [[CCDirector sharedDirector] winSize];

	int x = MAX(pos.x, winSize.width / 2);
    int y = MAX(pos.y, winSize.height / 2);

	x = MIN(x, (level.TileMapWidth)
			- winSize.width / 2);
    y = MIN(y, (level.TileMapHeight)
			- winSize.height/2);

	CGPoint actualPosition = ccp(x, y);

    CGPoint centerOfView = ccp(winSize.width/2, winSize.height/2);
    CGPoint viewPoint = ccpSub(centerOfView, actualPosition);

	self.position = viewPoint;
}

Posted 1 year ago #

rickms
Member

A method that works well for me is setting your box2d's body.userData equal to your hero object. Then while looping through the bodies in the tick method check for b->GetUserData() == myHero. If true, than do whatever you want to that object and do nothing on the others.

Having your game objects subclass CCSprite and include the box2d body in that object is a great way to keep everything organized.

Posted 1 year ago #
Jack Here
Member

Thanks for the tips.

@zangmobile: I got the scroll working correctingly, thanks.

@rickms: dont have my hero encapsulated yet, but I will definitely try something like you said.

If I do something with my hero, then destory that one, and create another-does 'jumping' to the location of the new one take more processing power then it would to scroll back to the new one?

Posted 1 year ago #
zangmobile
Member

@rickms that is a great idea thanks I can use that now.

Posted 1 year ago #
zangmobile
Member

@Jack I would be surprised if you see any real diff in performance. I would highly recommend not jumping if it looks bad. What does the fps show during this?

Posted 1 year ago #
Jack Here
Member

It stays at 60 fps.

Posted 1 year ago #

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