CODEWITHSUNDEEP
iossprite-kitskphysicsbody
ObjectiveCsam
ObjectiveCsam

Reputation: 204

SKPhysicBody In the Wrong position

I am creating a simple Sprite Kit game however when i am adding the PhysicsBody to one of my sprites it seems to be going in the wrong position. i know that it is in the wrong position as i have have set skView.showsPhysics = YES; and it is showing up in the wrong position.

enter image description here

The Square in the bottom corner is the physics body for the first semicircle. I am using a square at the moment just for testing purposes.

My app includes view following and follows my main sprite when it moves. I implemented this by following apples documentation and creating a 'myworld' node and creating all other nodes from that node. 

 myWorld = [SKNode node];

    [self addChild:myWorld];

 semicircle = [SKSpriteNode spriteNodeWithImageNamed:@"SEMICRICLE.png"];
    semicircle.size = CGSizeMake(semicircle.frame.size.width/10, semicircle.frame.size.height/10);
    semicircle.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:semicircle.frame.size];
    semicircle.position = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
    semicircle.physicsBody.dynamic = YES;
    semicircle.physicsBody.collisionBitMask = 0;
    semicircle.name = @"semicircle";
    [myWorld addChild:semicircle];

To centre on the node I call these methods

- (void)didSimulatePhysics
 {
[self centerOnNode: [self childNodeWithName: @"//mainball"]];
  }

  - (void) centerOnNode: (SKNode *) node
  {
CGPoint cameraPositionInScene = [node.scene convertPoint:node.position fromNode:node.parent];
node.parent.position = CGPointMake(node.parent.position.x - cameraPositionInScene.x,                                                   node.parent.position.y - cameraPositionInScene.y);
   }

I don't know if the my world thing makes any difference to the SkPhysics body...

Upvotes: 0

Views: 560

Answers (2)

Shed Brain
Shed Brain

Reputation: 1

Your centerOnNode call should be put in the didEvaluateActions function instead of the didSimulatePhysics function. This is because you need to move the world before the physics are drawn so that they stay in sync. Similar question found here: https://stackoverflow.com/a/24804793/5062806

Upvotes: 0

sangony
sangony

Reputation: 11696

SKPhysicsBody starts at coordinates 0,0 which is at the bottom left hand corner. If you make the area smaller, as you did by width/10 and height/10, you decrease the size but from the bottom left.

I think what you are looking for is bodyWithRectangleOfSize:center: which allows you to manually set the center from which you base your physics body area on.

Update:

Based on what I understand, your smallest semi circle pic size is the same as the screen size. I would suggest you modify the image size to something like the example I have. You can then set the sprite's position as required and set the physics body to the half of the image containing your semi circle. enter image description here

Upvotes: 2

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