Open Radar

 
Summary:
When running a physics simulation in SpriteKit, if you have a node with a physics body and a negative scale, the node will behave unpredictably in the sprite kit scene. In the gif provided, the static physics body at the bottom has a scale of {-1, -1}, and you can observe that the other node passes through it as if it weren't even there. If the scale were changed to {1, 1} they would behave correctly.

I have seen other behaviours with nodes in this case, such as all dynamic physics bodies being blown out of the scene when there was a {-1, -1} static physics body present, or a dynamic physics body experiencing a giant impulse and flying off the screen when colliding with another physics body whose scale was {-1, -1}

Steps to Reproduce:
1. Create a new game project selecting SpriteKit as the technology
2. Open GameScene.m 
3. Replace all code in the file with this minimal example:

@implementation GameScene

-(void)didMoveToView:(SKView *)view {
    SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:@"Spaceship"];

    sprite.xScale = -0.5;
    sprite.yScale = -0.5;
    sprite.position = CGPointMake(500, 250);
    [self addChild:sprite];
    sprite.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:sprite.size];
    sprite.physicsBody.dynamic = NO;

    SKSpriteNode *sprite2 = [SKSpriteNode spriteNodeWithImageNamed:@"Spaceship"];

    sprite2.xScale = 0.5;
    sprite2.yScale = 0.5;
    sprite2.position = CGPointMake(500, 500);
    [self addChild:sprite2];
    sprite2.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:sprite2.size];
    sprite2.physicsBody.dynamic = YES;
}

@end


Expected Results:
I would expect nodes with a negative scale to behave the same as nodes with positive scale, just to be visually reversed.

Actual Results:
In the gif provided, the static physics body at the bottom has a scale of {-1, -1}, and you can observe that the other node passes through it as if it weren't even there. If the scale were changed to {1, 1} they would behave correctly.

I have seen other behaviours with nodes in this case, such as all dynamic physics bodies being blown out of the scene when there was a {-1, -1} static physics body present, or a dynamic physics body experiencing a giant impulse and flying off the screen when colliding with another physics body whose scale was {-1, -1}

Version:
XCode: Version 6.1.1 (6A2008a), iOS: 8.1.3 (12B466)

Notes:
Although the outcome varies, problems occur 100% of the time if the scale is negative.