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SpriteKit uses a grid of points to position nodes. In this grid, the bottom left corner of the scene is (0,0), with a positive X-axis to the right and a positive Y-axis to the top. Similarly, on the individual sprite level, (0,0) refers to the bottom left corner of the sprite, while (1,1) refers to the top right corner.
Alignment with Anchor Points
Each sprite has an anchor point property, or an origin. The anchorPoint property allows you to choose which part of the sprite aligns to the sprite’s overall position.
The default anchor point is (0.5,0.5), so new SKSpriteNodes center perfectly on their position.