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How much does CGAffineTransformMakeRotation () cost?

Is this a very expensive feature that sucks my work under my feet? I guess they used this for the rotate buttons on the home screen + core animations. I just want to know before I start wasting my time;)

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As with everything, it depends on how and how you use it. It has been used all along in game development, for which the iPhone is very well suited. CoreAnimation is also very fast. If you're worried about that, my suggestion is to take one of the Apple apps that come with the examples and run it through the tools to prepare some of your own tests to make sure they are acceptable for your needs.



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It seems unlikely that this will be a big performance problem - it works for something like cosine, sine, and multiple multiplications. Don't call it a thousand times a second and you'll be fine.



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Very (very) little. This is also something that you can easily measure; see the following urls for examples / information on using high-res sync:

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All the CGAffineTransformMakeRotation () actually fill the matrix for a regular old CGAffineTransform. If you think you can fill (or pre-fill) the matrix faster then go for it (I'd be very surprised if this wasn't super-optimized already).

Then, when it comes time to do the actual work with the transform applied, I'm pretty sure the GPU is advised to take care of it so that it runs fast and your main processor doesn't have to take too much of a hit.

If you're really worried about it, do your 2D transforms on top of OpenGL to make sure it's optimized for hardware.

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I just want to know before I start wasting my time

Optimize the system, not single lines. Who knows how many times your code will trigger the conversion. Your best bet is to get the whole system to work, profile it, and then optimize the parts that are too slow.

Don't worry about individual calls that people say are slow. Use this information as a pointer if your code is slow, but always watch how your code works.

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