Changing center point of SKPhysicsBody while using 'bodyWithTexture' (SpriteKit)

It seems like the Spritekit's API does not allow to change the center of the physicsbody when using 'bodyWithTexture' (or maybe I'm missing something).

I'm wondering how you get around this when using a pixel precision physicsbody.

//Upper Claw
SKSpriteNode *claw = [SKSpriteNode spriteNodeWithImageNamed:BOSS_CLAW_SPRITE];
claw.position = CGPointMake(800, 520);
claw.anchorPoint = CGPointMake(1, .7);

//physics
claw.physicsBody = [SKPhysicsBody bodyWithTexture:claw.texture size:claw.size];

You can clearly see that the physicsbody's center position is where the anchor point is. enter image description here

Alternatively, bodyWithCircle / bodyWithRectangle have a 'center' property. However, it isn't as precise and needs a lot of code to make (unscalable).

-(SKPhysicsBody*)getPhysicsForClaw:(BOOL)isUpperClaw
{
     NSInteger reverseConstant = 1;
     if (!isUpperClaw) {
         reverseConstant = -1;
     }
     SKPhysicsBody *clawTip1 = [SKPhysicsBody bodyWithCircleOfRadius:5 center:CGPointMake(-545, -140*reverseConstant)];
     SKPhysicsBody *clawTip2 = [SKPhysicsBody bodyWithCircleOfRadius:6 center:CGPointMake(-540, -130*reverseConstant)];
     SKPhysicsBody *clawTip3 = [SKPhysicsBody bodyWithCircleOfRadius:7 center:CGPointMake(-535, -120*reverseConstant)];
     SKPhysicsBody *clawTip4 = [SKPhysicsBody bodyWithCircleOfRadius:8 center:CGPointMake(-530, -110*reverseConstant)];
     SKPhysicsBody *clawTip5 = [SKPhysicsBody bodyWithCircleOfRadius:8 center:CGPointMake(-525, -100*reverseConstant)];
     SKPhysicsBody *clawTip6 = [SKPhysicsBody bodyWithCircleOfRadius:9 center:CGPointMake(-515, -90*reverseConstant)];
     SKPhysicsBody *clawTip7 = [SKPhysicsBody bodyWithCircleOfRadius:11 center:CGPointMake(-508, -78*reverseConstant)];
     SKPhysicsBody *clawTip8 = [SKPhysicsBody bodyWithCircleOfRadius:12 center:CGPointMake(-495, -65*reverseConstant)];
     SKPhysicsBody *clawTip9 = [SKPhysicsBody bodyWithCircleOfRadius:13 center:CGPointMake(-480, -50*reverseConstant)];
     SKPhysicsBody *clawTip10 = [SKPhysicsBody bodyWithCircleOfRadius:14 center:CGPointMake(-465, -35*reverseConstant)];

     SKPhysicsBody *clawTeeth1 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(6, 40) center:CGPointMake(-433, -70)];
     SKPhysicsBody *clawTeeth2 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(15, 20) center:CGPointMake(-420, -60)];
     SKPhysicsBody *clawTeeth3 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(9, 40) center:CGPointMake(-395, -70)];
     SKPhysicsBody *clawTeeth4 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(15, 20) center:CGPointMake(-382, -60)];
     SKPhysicsBody *clawTeeth5 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(9, 40) center:CGPointMake(-345, -70)];
     SKPhysicsBody *clawTeeth6 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(10, 20) center:CGPointMake(-334, -60)];
     SKPhysicsBody *clawTeeth7 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(9, 30) center:CGPointMake(-295, -60)];
     SKPhysicsBody *clawTeeth8 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(9, 30) center:CGPointMake(-255, -42)];

     SKPhysicsBody *clawBody1 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(100, 45) center:CGPointMake(-400, -30)];
     SKPhysicsBody *clawBody2 = [SKPhysicsBody bodyWithCircleOfRadius:26 center:CGPointMake(-325, -25*reverseConstant)];
     SKPhysicsBody *clawBody3 = [SKPhysicsBody bodyWithCircleOfRadius:28 center:CGPointMake(-290, -12*reverseConstant)];
     SKPhysicsBody *clawBody4 = [SKPhysicsBody bodyWithCircleOfRadius:29 center:CGPointMake(-250, 0*reverseConstant)];
     SKPhysicsBody *clawBody5 = [SKPhysicsBody bodyWithCircleOfRadius:28 center:CGPointMake(-210, 10*reverseConstant)];
     SKPhysicsBody *clawBody6 = [SKPhysicsBody bodyWithCircleOfRadius:30 center:CGPointMake(-165, 24*reverseConstant)];

     SKPhysicsBody *clawBase1 = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(120, 55) center:CGPointMake(-75, 24)];

     SKPhysicsBody *claw = [SKPhysicsBody bodyWithBodies:@[clawTip1, clawTip2, clawTip3, clawTip4, clawTip5, clawTip6, clawTip7, clawTip8, clawTip9, clawTip10, clawTeeth1, clawTeeth2, clawTeeth3, clawTeeth4, clawTeeth5, clawTeeth6, clawTeeth7, clawTeeth8, clawBody1, clawBody2, clawBody3, clawBody4, clawBody5, clawBody6, clawBase1]];

     return claw;
 }

enter image description here

Solution

Anchor points have no effect on a physics body. There are a couple of physics bodies for which you can define a center point.

(SKPhysicsBody *)bodyWithCircleOfRadius:(CGFloat)r
                                 center:(CGPoint)center

(SKPhysicsBody *)bodyWithRectangleOfSize:(CGSize)s
                                  center:(CGPoint)center

Unfortunately the bodyWithTexture: has no such capability. As a hack you could use a number of various sized rectangles, rotate them to the desired angle and join them together with (SKPhysicsBody *)bodyWithBodies:(NSArray *)bodies. This will allow you to pretty much cover your texture.

As an added benefit, using rectangles instead of bodyWithTexture is also less of a burden to your FPS.