Changing the hitbox of an image

Question

I've been looking for a solution for quite a while now, but I can't help finding one. The situation is as following: I created an SKSpriteNode with an image, by the method touchesBegan I want to interact with it, like if one touches the image, something should change. The problem is that the hitbox around this image is square-shaped and not adjusted to the shape of the image. Has anyone got any clue how I can solve this problem? I tried doing it by changing the physicsBody like this

CGFloat offsetX = node.frame.size.width * node.anchorPoint.x;
CGFloat offsetY = node.frame.size.height * node.anchorPoint.y;

CGMutablePathRef path = CGPathCreateMutable();
CGPathCloseSubpath(path);

node.physicsBody = [SKPhysicsBody bodyWithPolygonFromPath:path];

Seems like the touchesBegan method doesn't use the physicsBody shape but the actual shape, I tried my best explaining it, sorry if I confused you.

Thanks in advance!

Julian

Answer 1

In the Xcode level editor, under the physics definition of your SKSpriteNode, change the body type to alpha mask (see image). This makes the physics boundary conform to the actual shape of your sprite rather than the rectangular bounding box.

Sadly, this solution only applies if your sprites are managed in an .sks file since level editor seems to have logic that calculates your sprite's outline and turns it into a path used to initialize the physics body with a body type of 'alpha mask'. (Too bad there's currently no 'bodyType' property on SKPhysicsBody because it would be really convenient to be able to set this programmatically instead of only being able to do so in the .sks file... Apple?)

The way you're attempting to create and initialize an SKPhysicsBody with a CGpath is on the right track I think... But since it's currently an empty path (having no points or lines) I'm guessing it won't have any effect.

Is there any way you could approximate some points & lines to represent a rough outline path for your sprite? Then, you could use those points to create a CGPath and then use that to initialize an SKPhysicsBody.

If not, a short-term compromise could be to initialize your SKPhysicsBody using init(circleOfRadius:) and use a circle as the body type which could seem less clunky than a box. And you could maybe play around with the circle radius to get a feel for the most natural radius for your collisions.