Is fast UILabel rotation possible?

Question

I want to work in landscape mode only and so far the only way I can get the appropriate coordinate frame in the rest of the application is by rotating the main window using:

CGAffineTransformMakeRotation(3.1415/2.0f);

which rotates all subviews as well.

It works great, except when I want to draw UILabel, frame rate drops like crazy. I need the truncation and all those pretty things that come with UILabel so my question is, is there a better way of going into landscape mode or speeding up the text drawing. I've seen some applications that work in landscape mode and still have text, so I wonder...

score 4 · Accepted Answer · answered Jan 24 '10 at 08:42

4

Maybe use CGAffineTransformMakeRotation(M_PI/2.0f); instead? This should produce a truly simple affine transform matrix.

answered Jan 24 '10 at 08:42

kennytm

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Oh wow that was it, thanks. :) I don't quite understand why though. Doesn't it still multiply out the rest of the elements in the matrix? – Dogan Demir Jan 24 '10 at 08:57
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With `M_PI/2.0f` your matrix is something like `[0, 1; -1, 0]`, while with `3.1415/2.0f` (an inaccurate value) you get `[4.6e-5, 0.99…; -0.99…, 4.6e-5]` which cause things very slow. – kennytm Jan 24 '10 at 10:03

score 2 · Answer 2 · edited May 23 '17 at 10:33

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If all that you want to do is work in landscape mode, as of iPhone OS 2.1 you don't need to apply a transform to your main view. See this answer to this question for more detail.

edited May 23 '17 at 10:33

Community

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answered Jan 24 '10 at 16:10

Brad Larson

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score 0 · Answer 3 · answered Oct 10 '11 at 11:38

Very Simple:

    myLabel.text = @"Text To Rotate";
    //myLabel is UILabel, which i want to Rotate.
    myLabel.textColor = self.xValuesColor;
    myLabel.backgroundColor = [UIColor redColor];
    myLabel.textAlignment = UITextAlignmentCenter;
    CATransform3D landscapeTransform = CATransform3DIdentity;
    landscapeTransform = CATransform3DRotate(landscapeTransform,-90, 0, 0, 1);
    // -90 is angle to rotate, you can change it according to your requirement. 
    myLabel.layer.transform = landscapeTransform;
    [self addSubview:myLabel];
    [myLabel release];

Is fast UILabel rotation possible?

3 Answers3