問題描述
CGAffineTransform：將比例應用於翻譯，如何？ (CGAffineTransform: apply a Scale to a Translation, how?)
The affine transforms Apple use have "scale" defined as "does not affect translation"
This seems to me completely wrong, and doesn't match what I'd expect from normal affine transforms (where a scale multiplied by a translation DOES affect the translation), and makes it extremely difficult to work with real‑world problems, where "scaling" is expected to scale the entire co‑ordinate system, not just the local co‑ords of a single object at a time.
Is there a safe way within Apple's library to workaround this problem (i.e. make "scale" apply to the whole matrix, not just the non‑translation parts)?
Or have I made a stupid mistake and completely misunderstood what's happening with the scaling, somehow?
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參考解法
方法 1:
I'm pretty sure that just means it doesn't affect the translation values in the matrix. CGAffineTransform isn't some special brand of math, it's just a regular transformation matrix. It works like any other transformation matrix you've ever used.
方法 2:
Ah. Embarassing. My mistake: arguments to concat were wrong way around! At least I can leave this here and hopefully help the next person to make such a dumb mistake.
I had a Concat call with the arguments the wrong way around; obviously, "translating" a "scale" works as expected ‑ the scale doesn't affect the translate!
When I googled this issue, I hit a couple of pages that talked about CGAffineTransform doing scale and translate independently. Confirmation bias :( I read that and assumed it was true. Doh.
FYI: CGAffineTransformConcat( A, B ) ... does: Matrix A * Matrix B ... i.e. "A's effects first, then B's effects"
So, make sure your scaling matrix is the second argument (or the "later" argument if you have a chain of nested Concat calls).
(by Adam、Lily Ballard、Adam)