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How to made an SKSpriteNode render faster using blendMode

Paul Hudson       @twostraws

All SpriteKit nodes have a blendMode property that describes how they should be drawn to the screen. The default value is .alpha, which means the sprite should be drawn so that its alpha transparency is respected – any parts that are translucent get blended with the existing background color at that point, and any fully transparent parts are not drawn at all.

Alpha drawing is obviously a sensible default, because it allows us to render sprites with irregular shapes and holes. However, if you know for a fact that your sprite is completely rectangular and has no holes then using .alpha is wasteful – SpriteKit is forced to do alpha blending even though it isn’t required. This is particularly common with background images: if they are designed to fill the full screen, there’s no need to make them drawing using .alpha.

To fix this – and make such drawing significantly faster – change the blend mode of opaque sprites to be .replace, which ignores any alpha in the texture:

background.blendMode = .replace

Available from iOS 7.0

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