SKPhysicsBody from a line (not closed polygon) - ios

Question

I am trying to create an SKPhysicsBody from a line drawn in the scene. This line is not a closed polygon, but simply created while tracking the users finger in touchesMoved. I need to create a physics body out of this line so that a ball bounces off of it as if it were a ledge, but I can't seem to figure out how to do that.
The closest thing I've found is bodyWithPolygonFromPath, but it only works when the line has been closed into a polygon.
I'm very new to iOS programming (this is my first project) so please take it easy!
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
[lineNode removeFromParent];
CGPathRelease(pathToDraw);
UITouch* touch = [touches anyObject];
CGPoint positionInScene = [touch locationInNode:self];
pathToDraw = CGPathCreateMutable();
CGPathMoveToPoint(pathToDraw, NULL, positionInScene.x, positionInScene.y);
lineNode = [SKShapeNode node];
lineNode.path = pathToDraw;
lineNode.strokeColor = [SKColor redColor];
[self addChild:lineNode];
}
- (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
UITouch* touch = [touches anyObject];
CGPoint positionInScene = [touch locationInNode:self];
CGPathAddLineToPoint(pathToDraw, NULL, positionInScene.x, positionInScene.y);
lineNode.path = pathToDraw;
}
- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event
{
lineNode.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:lineNode.path];
lineNode.physicsBody.categoryBitMask = paddleCategory;
lineNode.physicsBody.collisionBitMask = ballCategory | paddleCategory;
lineNode.physicsBody.contactTestBitMask = ballCategory | paddleCategory;
}

Answer 1

Does the line need to move or react to collisions, or just cause collisions?
If the former, you need a dynamic body — and a dynamic body has to have volume (well, area) so an open path won't work. In this case you could either loop the path back along itself to close it (probably easy to code but hard to make work right) or approximate the path with a collection of narrow rectangular bodies.
If the latter, a static body will do. You can create one from a line segment between two points with bodyWithEdgeFromPoint:toPoint:, or from a series of segments with bodyWithEdgeChainFromPath:.