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  1. PO
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    <p>you can fake it this way: create an affine transform that collapse the layer along it's diagonal:</p> <pre><code>A-----B B | | / | | -&gt; A&amp;D | | / C-----D C </code></pre> <p>change the image, and trasform the CALayer back in another animation. This will create the illusion of the layer rotating around its diagonal.</p> <p>the matrix for that should be if I remember math correctly:</p> <pre><code>0.5 0.5 0 0.5 0.5 0 0 0 1 </code></pre> <p>Update: ok, CA doen't really likes to use degenerate transforms, but you can approximate it this way:</p> <pre><code>CGAffineTransform t1 = CGAffineTransformMakeRotation(M_PI/4.0f); CGAffineTransform t2 = CGAffineTransformScale(t1, 0.001f, 1.0f); CGAffineTransform t3 = CGAffineTransformRotate(t2,-M_PI/4.0f); </code></pre> <p>in my tests on the simulator there still was a problem because the rotations happens faster than te translation so with a solid black square the effect was a bit weird. I suppose that if you have a centered sprite with transparent area around it the effect will be close to what expected. You can then tweak the value of the <strong>t3</strong> matrix to see if you get a more appealing result.</p> <p>after more research, it appears that one should animate it's own transition via keyframes to obtaim the maximum control of the transition itself. say you were to display this animation in a second, you should make ten matrix to be shown at each tenth of a second withouot interpolation using kCAAnimationDiscrete; those matrix can be generated via the code below:</p> <pre><code>CGAffineTransform t1 = CGAffineTransformMakeRotation(M_PI/4.0f); CGAffineTransform t2 = CGAffineTransformScale(t1, animationStepValue, 1.0f); CGAffineTransform t3 = CGAffineTransformRotate(t2,-M_PI/4.0f); </code></pre> <p>where animationStepValue for ech of the keyFrame is taken from this progression:</p> <pre><code>{1 0.7 0.5 0.3 0.1 0.3 0.5 0.7 1} </code></pre> <p>that is: you're generating ten different transformation matrix (actually 9), pushing them as keyframes to be shown at each tenth of a second, and then using the "don't interpolate" parameter. you can tweak the animation number for balancing smoothness and performance*</p> <p>*sorry for possible errors, this last part was written without a spellchecker.</p>
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    1. POHow do i rotate a CALayer around a diagonal line?
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    1. USLorenzo Boccaccia
    1. USLorenzo Boccaccia
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    1. POHow do i rotate a CALayer around a diagonal line?
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    1. COThanks for your answer. Is the ASCII-art suppose to show a shear transformation? if I try to animate from identity, then to your matrix and them back to identity i get no image at all :( I looked up how to make a shear matrix and it look like this: {{1, sheary, 0}, {shearx, 1, 0}, {0, 0, 1}} If I use that in the animation it seams to work a bit but i need to shear quite much and then the image gets scaled up quite a bit too.
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      1. USMattias Wadman
    2. COno shear will make a parallelogram, here we're trying to get a degenerated rhombus, with the A&D corner moving towards the center and not the A&B corners moving toward left I'll have to try this on the device tomorrow to get the actual matrix parameters
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      1. USLorenzo Boccaccia
    3. COOk. I have been reading how affine transformations actually work and the transformation you describe with the diagram should as you say be affine, preserving points on a line and ratios (as long as A and D are "opposites" i guess?). But I havent really figured how to think about the numbers in the matrix.
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      1. USMattias Wadman
 

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