Coordinate system in Sprite Kit

SpriteKit coordinates

The coordinate system in Sprite Kit might give you a headache if you didn’t dig deep enough while reading the documentation.

In this post I will explain differences between SKScene and SKNode when it comes to coordinate system in Sprite Kit.

SKScene

Sprite Kit uses a coordinate system orientation that starts from the bottom left corner of the screen (0, 0), and the x and y values increase as you move up and to the right.

For SKScene, the default value of the origin – anchorPoint is (0, 0), which corresponds to the lower-left corner of the view’s frame rectangle. To change it to center you can specify (0.5, 0.5).

SKNode

The coordinate system origin in the SKNode is defined by its anchorPoint which by default is (0.5, 0.5) which is center of the node.

But why is it center? The texture of the sprite is drawn relative to the node position based on the anchorPoint factor. It’s default value of (0.5, 0.5) places the texture centered on the node’s position. You might want to adjust the anchor point, but it will change the position of the texture which you generally don’t want.

When creating a CGPath for a physics body for your SKNode (for example using bodyWithEdgeLoopFromPath: method) you should use node’s coordinate system with the origin in the middle unless you changed the anchor point.

Tricks

You can set SKScene‘s yScale property to -1. If you do so, everything will render upside down. Moreover, you can also set the yScale property for each SKNode to -1, which will cause them to render right side up.

Things to remember

  • SKNodes have a default coordinate system where (0, 0) is the center.
  • SKScene has a default coordinate system where (0, 0) is the lower left corner.

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