UIImage from any CALayer/UIView

[Sbrocket]

This is something I employ to speed up animations during autorotation. You can get a UIImage to use as you want (such as in a fullscreen UIImageView, as I do) from any CoreAnimation layer (CALayer). Since every UIView has an associated CALayer, you can basically take a snapshot of the current state of any UIView.

UIGraphicsBeginImageContext(myView.bounds.size);
[myView.layer renderInContext:UIGraphicsGetCurrentContext()];
viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

If you have a CALayer rather than a UIView that you want to render, you would simply send the layer renderInContext: directly and use the layer bounds instead of the view bounds.

Currently there is a bug (rdar://6018652) where -[CALayer renderInContext:] is not recognized by the compiler so you will get a warning when using this. The method does definitely exist, though, and its in the headers.

EDIT: Its not actually a bug. Just make sure you import and link in QuartzCore.framework where you use this.

[go2]

Add this line to the end and you can save the image to your photo library -

UIImageWriteToSavedPhotosAlbum(viewImage, self, nil, nil);

or if you need a callback:

UIImageWriteToSavedPhotosAlbum(viewImage, self, (SEL)@selector(viewImage:didFinishSavingWithError: contextInfo:), nil);

- (void)image:(UIImage *)image
didFinishSavingWithError:(NSError *)error
contextInfo:(void *)contextInfo;

[errrick]

WOW, this is sick, exactly what I needed!

I had a rotating UITable with lots of rows at 20px height each.. and the rotate effect was painfully slow.. I wonder how Safari managed to do such smooth rotation even on the most overloaded websites, I guess this is the method it uses ?

big thanks, will try it when I get home.

[Sbrocket]

Originally Posted by errrick

WOW, this is sick, exactly what I needed!

I had a rotating UITable with lots of rows at 20px height each.. and the rotate effect was painfully slow.. I wonder how Safari managed to do such smooth rotation even on the most overloaded websites, I guess this is the method it uses ?

big thanks, will try it when I get home.

Its certainly possible. I know the Calculator on the iPhone is actually just one big UIImageView with overlays for when you press the buttons, which is why it animates so smoothly.

[ScottYelich]

well, if you do cache.. it generates a static image and then rotates that... if not, it renders for each frame... right? so, was it slow without using cache or with? If that description above is accurate -- all rotations should be the same speed.

[TheArsenik]

Hi,
When I found this code, I thought "cool that's all I need" but visibly not.
I have a UIImageView which is an animation:

UIImageView *myImage=[[UIImageView alloc] InitWithFrame:CGRectMake(0.0, 0.0, 100.0, 100.0)];
myImage.imageView.animationImages= [NSArray arrayWithObjects:[UIImage imageNamed:@"foo1.png"],
                                    [UIImage imageNamed:@"foo2.png"],nil];
		imageView.animationDuration=0.7;
		imageView.animationRepeatCount=0;
[myImage startAnimating];

Now, when the user touch the Iphone screen, I want to know if the pixel he touched was visible or not (my PNG images are RGBA files).
So I tryed with the previous sample...:

UIGraphicsBeginImageContext(myImage.bounds.size);
[myImage.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *snapshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

but when I tried to display snapshot, I have nothing.
So I've tested this code on another UIImageView like this:

UIImageView *myImage=[[UIImageView alloc] InitWithFrame:CGRectMake(0.0, 0.0, 100.0, 100.0)];
myImage.imageView.animationImages= [NSArray arrayWithObjects:[UIImage imageNamed:@"foo1.png"],
                                    [UIImage imageNamed:@"foo2.png"],nil];
myImage.image=[UIImage imageNamed:@"foo3.png"]
		imageView.animationDuration=0.7;
		imageView.animationRepeatCount=0;
[myImage startAnimating];

And this give me a snapshot of foo3.png which is not what I want.
So have you got any idea how can I get the current image played?
I tried also with a timer which would indicate me time elapsed since the beginning of the animation but it's a bad solution and it doesn't work too.
Thanks for your replies.