Why does Sprite Kit SKNode expose zRotation, xScale and yScale instead of simply a transform?

Question

Sprite Kit relies on zRotation, xScale and yScale instead of simply a transform property. Is it because Apple needs the rotation and scale values to compute physics with higher performance?

Or why else would they not simply expose a transform property instead of individual properties for rotation and scale?

Answer 1

Because they put themselves in the mindset of the (majority) of potential users:

WTF is a transform???

Eeeeew, math!

Why aren't there just rotation, position and scale properties???

Why does this have to be so hard?

Sprite Kit sucks!!!1

For anyone besides a small group of programmers and mathematicians these properties are naturally expressed as rotation, scale, position. Everyone understands them, everyone can use them, and the math used to transform them is simple and widely documented, ie rotation around a point with cos(x)/sin(y). Trigonometry is manageable.

Those wanting to use transforms will find no difficulty in converting these properties from and to transforms. Transforms are an advanced concept, more powerful but also more difficult to use.

Now tell the Transformians that they'll have to use raw quaternions for all their calculations. Same thing, just on a higher level. ;)

Other aspects:

• the CGTransform API is neither Objective-C nor ARC
• the physics engine (Box2D) has no concept of transforms either
• cocos2d had no transform properties either (they're only used internally), Sprite Kit is modelled after cocos2d.
• transforms are not commonly used in other 2D render engines either