I&#39;m using the new ImageIO framework in iOS 4.1. I successfully retrieve the exif metadata using the following:

    CFDictionaryRef metadataDict = CMGetAttachment(sampleBuffer, kCGImagePropertyExifDictionary , NULL);

Reading it out, it appears valid. Saving an image out works, but there is never any exif data in the image.

        CGImageDestinationRef myImageDest = CGImageDestinationCreateWithURL((CFURLRef) docurl, kUTTypeJPEG, 1, NULL);
        
        // Add the image to the destination using previously saved options. 
        CGImageDestinationAddImage(myImageDest, iref, NULL);
        
        //add back exif
        NSDictionary *props = [NSDictionary dictionaryWithObjectsAndKeys:
                                [NSNumber numberWithFloat:.1], kCGImageDestinationLossyCompressionQuality,
                               metadataDict, kCGImagePropertyExifDictionary, //the exif metadata
                                                            nil];
                               
                              //kCGImagePropertyExifAuxDictionary
        
        CGImageDestinationSetProperties(myImageDest, (CFDictionaryRef) props);
        
        // Finalize the image destination. 
        bool status = CGImageDestinationFinalize(myImageDest);



Problem setting exif data for an image

I&#39;m confusing `CGLayer` and `CALayer`. They look similar, so why are there separate implementations? What&#39;s the difference between, and compatibility of, `CGLayer` and `CALayer`?

What&#39;s the difference and compatibility of CGLayer and CALayer?

Hi i am searching a clean solution without overwriting `drawRect` or stuff like that to create a `UIView` with Rounded corners on the Top of the **View**. My main problem here is to create variable solution if the view is getting resized or something like that.
Is there a clean solution? **Apple** is this doing too on the first table item. it can&#39;t be so hard to do this.

Rounded Corners only on Top of a UIView

I need to create a rectangle that have just two rounded corners in swift (Objective C code also ok).

At the moment my code is creating two rectangles with 

    CGPathCreateWithRoundedRect(CGRectMake(0, 0, 30, 60), 5, 5, nil);

and 

    CGPathCreateWithRoundedRect(CGRectMake(0, 0, 30, 60), 0, 0, nil);

and merging them (to have two right angle corners and two rounded ones) but I am not happy with the code and I am pretty sure there should be much better ways to do it.

I am new to iOS and graphical development and swift.

Create a rectangle with just two rounded corners in swift?

so--i switched on &quot;color misaligned images&quot; to improve drawing performance in our app. The documentation states: 

&gt; Puts a magenta overlay over images
&gt; whose source pixels aren&#39;t aligned to
&gt; destination pixels

I don&#39;t know what the yellow means however. (There is a &quot;Color Offscreen-Rendered&quot; option that uses yellow... does &quot;Color Misaligned Images&quot; also turn on this option?)

Anybody know?

TIA

What does yellow tinting represent when using &quot;color misaligned images&quot; on iPhone/iOS

We&#39;ve stumbled upon a performance problem with Quartz Events, more specifically CGEventPost: during heavy GPU load CGEventPost can block. We&#39;ve created [a small benchmark application to demonstrate the issue][1]. This application is just a loop that creates, post and releases events.

Below you can see the results of running the application. The first run is on an idle system. The second run is with FurMark (GPU stress test) with the dials cranked up as much as possible.

* Inner is how long the inner loop takes, basically just creating, posting and releasing an event with Quartz Events.
* Outer is how long our program is waiting to be woken up (a sleep). Should be close to the time we sleep, but if the system is under pressure it could be delayed.
* Post is how long the event post takes.

&amp;nbsp;

	18:58:01.683 EventPerformance[4946:707] Measurements: (outer should be close to 10)
	18:58:01.684 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 11.02, CGEventPost (ms): 0.03
	18:58:01.684 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 11.02, CGEventPost (ms): 0.03
	18:58:01.685 EventPerformance[4946:707] inner (ms): 0.07, outer (ms): 10.26, CGEventPost (ms): 0.03
	18:58:01.685 EventPerformance[4946:707] inner (ms): 0.06, outer (ms): 10.85, CGEventPost (ms): 0.05
	18:58:01.686 EventPerformance[4946:707] inner (ms): 0.07, outer (ms): 10.41, CGEventPost (ms): 0.04
	18:58:01.686 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 10.39, CGEventPost (ms): 0.03
	18:58:01.686 EventPerformance[4946:707] inner (ms): 0.05, outer (ms): 11.02, CGEventPost (ms): 0.03
	18:58:01.687 EventPerformance[4946:707] inner (ms): 0.03, outer (ms): 10.67, CGEventPost (ms): 0.03
	18:58:01.687 EventPerformance[4946:707] inner (ms): 0.08, outer (ms): 10.09, CGEventPost (ms): 0.05
	18:58:01.688 EventPerformance[4946:707] Averages: (outer should be close to 10)
	18:58:01.688 EventPerformance[4946:707] avg inner (ms): 0.05, avg outer (ms): 10.64, avg post (ms): 0.03


Here we can see that posting the event takes about 0.03 ms on average. Also the thread seems to be woken up around 0.5ms too late. No spikes in CGEventPost.

	19:02:02.150 EventPerformance[5241:707] Measurements: (outer should be close to 10)
	19:02:02.151 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.23, CGEventPost (ms): 0.02
	19:02:02.151 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.54, CGEventPost (ms): 0.02
	19:02:02.151 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 11.01, CGEventPost (ms): 0.01
	19:02:02.152 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.74, CGEventPost (ms): 0.01
	19:02:02.152 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.20, CGEventPost (ms): 0.01
	19:02:02.152 EventPerformance[5241:707] inner (ms): 10.35, outer (ms): 11.01, CGEventPost (ms): 10.35
	19:02:02.152 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.02, CGEventPost (ms): 0.02
	19:02:02.153 EventPerformance[5241:707] inner (ms): 58.90, outer (ms): 10.11, CGEventPost (ms): 58.90
	19:02:02.153 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.12, CGEventPost (ms): 0.02
	19:02:02.153 EventPerformance[5241:707] Averages: (outer should be close to 10)
	19:02:02.371 EventPerformance[5241:707] avg inner (ms): 7.71, avg outer (ms): 10.44, avg post (ms): 7.71

When the system is under heavy GPU load, posting an event can take (spikes) milliseconds instead of microseconds. Under extreme GPU stress (&lt; 1 FPS), this value can take seconds. CGEventPost _sometimes_  seems to be waiting for the GPU to finish some work before returning. Our thread is still scheduled normally with no noticeable delay/spikes (outer).

Any ideas are appreciated.


  [1]: http://smoothmouse.com/storage/EventPerformance.zip

Weak performance of CGEventPost under GPU load

I am trying to merge two different images and create a new one. This is the way I would like to do:
I have this image (A):

[![polaroid][1]][1]


It&#39;s a PNG image and I would like to merge this one with another image (B) which I took from the phone to create something like this:

[![polaroid merged][2]][2]

I need a function who merge A with B creating C. The size must remain from the A image and the image B should auto adapt the size to fit into the polaroid (A). Is it possible to do that? Thank for your help!

**UPDATE**
Just one thing, the image (A) is a square and the image i took is a 16:9, how can i fix that?? If i use your function the image (B) that i took become stretched!

  [1]: http://i.stack.imgur.com/g70aw.png
  [2]: http://i.stack.imgur.com/UTxVP.png

How to merge two UIImages?

I&#39;m currently implementing a `CABasicAnimation` that animates a `CALayer` `transform` property.
Now, although I&#39;m new to Core Animation, I have been able to gather through various blogs and articles such as objc.io that it is a very bad idea to use the often (incorrectly) recommended method for getting animations to stick using the `fillMode` and `removedOnCompletion` properties of an animation. This method is considered bad practice by many because it creates a discrepancy between the model layer and the presentation layer, and so future queries to one of those layers may not match up with what the user is seeing.

Instead, the recommended way of doing animations is to update the model layer at the same time you add the animation to the layer being animated. However, I&#39;m having trouble understanding exactly how this is working. My animation is simple, and goes like this:

    CATransform3D updatedTransform = [self newTransformWithCurrentTransform];
    // Location 1
    CABasicAnimation *transformAnimation = [CABasicAnimation animationWithKeyPath:@&quot;transform&quot;];
    transformAnimation.duration = 1;
    transformAnimation.fromValue = [NSValue valueWithCATransform3D:self.layerBeingAnimated.transform]; // Does not work without this.
    transformAnimation.toValue = [NSValue valueWithCATransform3D:updatedTransform];
    // Location 2
    [self.layerBeingAnimated addAnimation:transformAnimation forKey:kTransformAnimationKey];
    // Location 3

I&#39;ve denoted three locations where I have attempted to update the model layer using the code
         
    self.layerBeingAnimated.transform = updatedTransform;

In location 1, the layer jumps right to `newTransform` and does not animate.
In location 2, the layer animates exactly as I want it to from the current transform to `newTransform`.
In location 3, the layer jumps right to `newTransform`, jumps back to the the old transform, animates correctly from the fromValue to newTransform, and then stays at `newTransform`.

What&#39;s the deal here? What&#39;s the correct location to update the model layer and why are these three locations producing such different results?

Thanks!

CABasicAnimation does not animate correctly when I update model layer

I&#39;ve read as many search results I could find on this dreaded problem, unfortunatelly, each one seems to focus on a specific function call.

My problem is that I get the same error from multiple functions, which I am guessing are being called back from functions that I use.

To make matters worse, the actual code is within a custom private framework which is being imported in another project, and as such, debugging isn&#39;t as simple?

Can anyone point me to the right direction? I have a feeling I&#39;m calling certain methods wrongly or with bad context, but the output from xcode is not very helpful at this point.


&gt; &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0. This is
&gt; a serious error. This application, or a library it uses, is using an
&gt; invalid context  and is thereby contributing to an overall degradation
&gt; of system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; &lt;Error&gt;: CGContextSetStrokeColorWithColor: invalid context 0x0. This
&gt; is a serious error. This application, or a library it uses, is using
&gt; an invalid context  and is thereby contributing to an overall
&gt; degradation of system stability and reliability. This notice is a
&gt; courtesy: please fix this problem. It will become a fatal error in an
&gt; upcoming update.
&gt; 
&gt; CGContextSaveGState: invalid context 0x0. This is a serious error.
&gt; This application, or a library it uses, is using an invalid context 
&gt; and is thereby contributing to an overall degradation of system
&gt; stability and reliability. This notice is a courtesy: please fix this
&gt; problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; &lt;Error&gt;: CGContextSetFlatness: invalid context 0x0. This is a serious
&gt; error. This application, or a library it uses, is using an invalid
&gt; context  and is thereby contributing to an overall degradation of
&gt; system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; 
&gt; &lt;Error&gt;: CGContextAddPath: invalid context 0x0. This is a serious
&gt; error. This application, or a library it uses, is using an invalid
&gt; context  and is thereby contributing to an overall degradation of
&gt; system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; &lt;Error&gt;: CGContextDrawPath: invalid context 0x0. This is a serious
&gt; error. This application, or a library it uses, is using an invalid
&gt; context  and is thereby contributing to an overall degradation of
&gt; system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; 
&gt; &lt;Error&gt;: CGContextRestoreGState: invalid context 0x0. This is a
&gt; serious error. This application, or a library it uses, is using an
&gt; invalid context  and is thereby contributing to an overall degradation
&gt; of system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.
&gt; 
&gt; 
&gt; &lt;Error&gt;: CGContextGetBlendMode: invalid context 0x0. This is a serious
&gt; error. This application, or a library it uses, is using an invalid
&gt; context  and is thereby contributing to an overall degradation of
&gt; system stability and reliability. This notice is a courtesy: please
&gt; fix this problem. It will become a fatal error in an upcoming update.

Those errors may occur when a custom view is presented, or one of its inherited classes. At which point they spawn multiple times, until the keyboard won&#39;t provide any input. Touch events are still registered, but system slows down, and eventually may lead to unallocated object errors.

**EDIT #1:** I do have access to the framework being imported, but I do not see anything weird in the classes which causing the issue.

**EDIT #2:** I just received an email that iOS 7.1 has been released for developers. I&#39;m curious to see if this goes away, or become worse, or can be solved.


invalid context 0x0 under iOS 7.0 and system degradation

I have a UIImage (Cocoa Touch). From that, I&#39;m happy to get a CGImage or anything else you&#39;d like that&#39;s available. I&#39;d like to write this function:

    - (int)getRGBAFromImage:(UIImage *)image atX:(int)xx andY:(int)yy {
      // [...]
      // What do I want to read about to help
      // me fill in this bit, here?
      // [...]
    
      int result = (red &lt;&lt; 24) | (green &lt;&lt; 16) | (blue &lt;&lt; 8) | alpha;
      return result;
    }

How to get pixel data from a UIImage (Cocoa Touch) or CGImage (Core Graphics)?

I&#39;ve been bashing my face into this one for literally days now and even though I feel constantly that I am right on the edge of revelation, I simply cannot achieve my goal.

I thought, ahead of time in the conceptual phases of my design, that it would be a trivial matter to grab a image from the iPhone&#39;s camera or library, scale it down to a specified height, using a function equivalent to the **Aspect Fill** option of UIImageView (entirely in code), and then **crop off** anything that did not fit within a passed CGRect.

Getting the original image from camera or library, was trivial. I am shocked at how difficult the other two steps have proved to be.

The attached image shows what I am trying to achieve. Would someone please be kind enough to hold my hand? Every code example I have found so far seems to smash the image, be upside down, look like crap, draw out of bounds, or otherwise just not work correctly.

UIImage: Resize, then Crop

I have this practice project that allows the user to draw on the screen as they touch with their fingers. Very simple App I did as an exercise way back.
My little cousin took the liberty of drawing things with his finger with my iPad on this App (Kids drawings: circle, lines, etc, whatever came to his mind).
Then he started to draw circles and then he asked me to make it a &quot;good circle&quot; (from my understanding: make the drawn circle perfectly round, as we know 
no matter how stable we try to draw something with our finger on the screen, a circle is never really as rounded as a circle should be). 

So my question here is that, is there any way in code where we can first detect a line drawn by the user that forms a circle and generate approximately the same size of the circle by making it perfectly round on the screen. Making a not so straight line straight is something I would know how to do, but as for circle, I don&#39;t quite know how to go about doing it with Quartz or other methods. 

My reasoning is that, the start and the end point of the line must touch or cross each other after the user lifts his finger to justify the fact that he was trying to actually draw a circle.


Draw a perfect circle from user&#39;s touch

Does anyone know why `CGContextDrawImage` would be drawing my image upside down? I am loading an image in from my application:

    UIImage *image = [UIImage imageNamed:@&quot;testImage.png&quot;];

And then simply asking core graphics to draw it to my context:

    CGContextDrawImage(context, CGRectMake(0, 0, 145, 15), image.CGImage);

It renders in the right place, and dimensions, but the image is upside down. I must be missing something really obvious here?

CGContextDrawImage draws image upside down when passed UIImage.CGImage

I have a `UIImage` that is `UIImageOrientationUp` (portrait) that I would like to rotate counter-clockwise by 90 degrees (to landscape). I don&#39;t want to use a `CGAffineTransform`. I want the pixels of the `UIImage` to actually shift position. I am using a block of code (shown below) originally intended to resize a `UIImage` to do this. I set a target size as the current size of the `UIImage` but I get an error:

&gt; (Error): CGBitmapContextCreate: invalid data bytes/row: should be at least 1708 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedLast.

(I don&#39;t get an error whenever I provide a SMALLER size as the target size BTW). How can I ROTATE my `UIImage` 90 degrees CCW using just core graphics functions while preserving the current size?


    -(UIImage*)reverseImageByScalingToSize:(CGSize)targetSize:(UIImage*)anImage
    {
    	UIImage* sourceImage = anImage; 
    	CGFloat targetWidth = targetSize.height;
    	CGFloat targetHeight = targetSize.width;
    	
    	CGImageRef imageRef = [sourceImage CGImage];
    	CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    	CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
    	
    	if (bitmapInfo == kCGImageAlphaNone) {
    		bitmapInfo = kCGImageAlphaNoneSkipLast;
    	}
    	
    	CGContextRef bitmap;
    	
    	if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
    		bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
    		
    	} else {
    		
    		
    		bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
    		
    	}       
    
    	
    	if (sourceImage.imageOrientation == UIImageOrientationRight) {
    		CGContextRotateCTM (bitmap, radians(90));
    		CGContextTranslateCTM (bitmap, 0, -targetHeight);
    		
    	} else if (sourceImage.imageOrientation == UIImageOrientationLeft) {
    		CGContextRotateCTM (bitmap, radians(-90));
    		CGContextTranslateCTM (bitmap, -targetWidth, 0);
    		
    	} else if (sourceImage.imageOrientation == UIImageOrientationDown) {
    		// NOTHING
    	} else if (sourceImage.imageOrientation == UIImageOrientationUp) {
    		CGContextRotateCTM (bitmap, radians(90));
    		CGContextTranslateCTM (bitmap, 0, -targetHeight);
    	}
    	
    	CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
    	CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    	UIImage* newImage = [UIImage imageWithCGImage:ref];
    	
    	CGContextRelease(bitmap);
    	CGImageRelease(ref);
    	
    	return newImage; 
    }
















How to Rotate a UIImage 90 degrees?

I was looking to be able to turn any UIColor into a gradient. The way I am intending to do this is by using Core Graphics to draw a gradient. What I am trying to do is to get a color, lets say:

    [UIColor colorWithRed:0.5 green:0.5 blue:0.5 alpha:1.0];
and get a UIColor which is a few shades darker and a few shades lighter. Does anyone know how to do this? Thank you.

Get Slightly Lighter and Darker Color from UIColor

**To clarify the purpose of this question: I know HOW to create complicated views with both subviews and using drawRect. I&#39;m trying to fully understand the when&#39;s and why&#39;s to use one over the other.**

I also understand that it doesn&#39;t make sense to optimize that much ahead of time, and do something the more difficult way before doing any profiling. Consider that I&#39;m comfortable with both methods, and now really want a deeper understanding.

A lot of my confusion comes from learning how to make table view scroll performance really smooth and fast. Of course the original source of this method is from the [author behind twitter][1] for iPhone (formerly tweetie). **Basically it says that to make table scrolling buttery smooth, the secret is to NOT use subviews, but instead do all the drawing in one custom uiview.** Essentially it seems that using lots of subviews slows rendering down because they have lots of overhead, and are constantly re-composited over their parent views.

To be fair, this was written when the 3GS was pretty brand spankin new, and iDevices have gotten much faster since then. Still [this method][2] is [regularly][3] [suggested][4] on the [interwebs][5] and elsewhere for high performance tables. In fact it&#39;s a suggested method in [Apple&#39;s Table Sample Code][6], has been suggested in several WWDC videos ([Practical Drawing for iOS Developers][7]), and many iOS [programming books][8].

There are even [awesome looking tools][9] to design graphics and generate Core Graphics code for them.

**So at first I&#39;m lead to believe &quot;there’s a reason why Core Graphics exists. It’s FAST!&quot;**

But as soon as I think I get the idea &quot;Favor Core Graphics when possible&quot;, I start seeing that drawRect is often responsible for poor responsiveness in an app, is extremely expensive memory wise, and really taxes the CPU. Basically, that I should &quot;[Avoid overriding drawRect][10]&quot; (WWDC 2012 [iOS App Performance: Graphics and Animations][11])

So I guess, like everything, it&#39;s complicated. Maybe you can help myself and others understand the When&#39;s and Why&#39;s for using drawRect?

I see a couple obvious situations to use Core Graphics:

 1. You have dynamic data (Apple&#39;s Stock Chart example)
 2. You have a flexible UI element that can&#39;t be executed with a simple resizable image
 3. You are creating a dynamic graphic, that once rendered is used in multiple places

I see situations to avoid Core Graphics:

 1. Properties of your view need to be animated separately
 2. You have a relatively small view hierarchy, so any perceived extra effort using CG isn&#39;t worth the gain
 3. You want to update pieces of the view without redrawing the whole thing
 4. The layout of your subviews needs to update when the parent view size changes

**So bestow your knowledge. In what situations do you reach for drawRect/Core Graphics (that could also be accomplished with subviews)? What factors lead you to that decision? How/Why is drawing in one custom view recommended for buttery smooth table cell scrolling, yet Apple advises drawRect against for performance reasons in general? What about simple background images (when do you create them with CG vs using a resizable png image)?**

A deep understanding of this subject may not be needed to make worthwhile apps, but I don&#39;t love choosing between techniques without being able to explain why. My brain gets mad at me.

## Question Update ##

Thanks for the information everyone. Some clarifying questions here:

 1. If you are drawing something with core graphics, but can accomplish the same thing with UIImageViews and a pre-rendered png, should you always go that route?
 2. A similar question: Especially with [badass tools like this][12], when should you consider drawing interface elements in core graphics? (Probably when the display of your element is variable. e.g. a button with 20 different color variations. Any other cases?)
 3. Given my understanding in my answer below, could the same performance gains for a table cell possibly be gained by effectively capturing a snapshot bitmap of your cell after your complex UIView render&#39;s itself, and displaying that while scrolling and hiding your complex view? Obviously some pieces would have to be worked out. Just an interesting thought I had.


  [1]: http://atebits.tumblr.com/post/197580827/fast-scrolling-in-tweetie-with-uitableview
  [2]: http://engineering.twitter.com/2012/02/simple-strategies-for-smooth-animation.html
  [3]: http://volonbolon.net/post/634453483/optimizing-table-views-for-performance
  [4]: http://blog.giorgiocalderolla.com/2011/04/16/customizing-uitableviewcells-a-better-way/#comment-208
  [5]: http://nachbaur.com/blog/core-graphics-isnt-scary-honest
  [6]: http://developer.apple.com/library/ios/#samplecode/TableViewSuite/Listings/5_CustomTableViewCell_Classes_TimeZoneView_m.html#//apple_ref/doc/uid/DTS40007318-5_CustomTableViewCell_Classes_TimeZoneView_m-DontLinkElementID_42
  [7]: https://developer.apple.com/videos/wwdc/2011/?id=129
  [8]: http://www.amazon.com/iOS-Programming-Pushing-Limits-ebook/dp/B00AJPDJMC/ref=sr_1_2?ie=UTF8&amp;qid=1359786019&amp;sr=8-2&amp;keywords=ios6%20pushing%20the%20limits
  [9]: http://www.paintcodeapp.com
  [10]: http://screencast.com/t/jVbYIKiI
  [11]: https://developer.apple.com/videos/wwdc/2012/?id=238
  [12]: http://www.paintcodeapp.com

to drawRect or not to drawRect (when should one use drawRect/Core Graphics vs subviews/images and why?)

I have designed UI elements in sketch, and one of them has a shadow with blur 1 and spread 0. I looked at the doc for the views layer property and layer doesn&#39;t have anything named spread or blur, or anything equivalent (the only control was merely shadowOpacity). How can control things like blur and spread?

Here are my settings in Sketch:

[![Sketch shadow settings][1]][1]

And here is what I want my shadow to look like:

[![Shadow wanted][2]][2]

And here is what it looks like at the moment:

[![Current shadow][3]][3]

Note, you have to click on the picture to actually see the shadow.

My code is as follows:

    func setupLayer(){
        view.layer.cornerRadius = 2
        view.layer.shadowColor = Colors.Shadow.CGColor
        view.layer.shadowOffset = CGSize(width: 0, height: 1)
        view.layer.shadowOpacity = 0.9
        view.layer.shadowRadius = 5
    }

  [1]: http://i.stack.imgur.com/NwHOY.png
  [2]: http://i.stack.imgur.com/pGNYw.png
  [3]: http://i.stack.imgur.com/teylM.png

How to control shadow spread and blur?

I would like to create a 1x1 UIImage dynamically based on a UIColor.

I suspect this can quickly be done with Quartz2d, and I&#39;m poring over the documentation trying to get a grasp of the fundamentals.  However, it looks like there are a lot of potential pitfalls:  not identifying the numbers of bits and bytes per things correctly, not specifying the right flags, not releasing unused data, etc.

How can this be safely done with Quartz 2d (or another simpler way)?

How to create a colored 1x1 UIImage on the iPhone dynamically?

All I want is a one pixel black border around my white UILabel text. 

I got as far as subclassing UILabel with the code below, which I clumsily cobbled together from a few tangentially related online examples. And it works but it&#39;s very, very slow (except on the simulator) and I couldn&#39;t get it to center the text vertically either (so I hard-coded the y value on the last line temporarily). Ahhhh!

    void ShowStringCentered(CGContextRef gc, float x, float y, const char *str) {
        CGContextSetTextDrawingMode(gc, kCGTextInvisible);
        CGContextShowTextAtPoint(gc, 0, 0, str, strlen(str));
        CGPoint pt = CGContextGetTextPosition(gc);
	
        CGContextSetTextDrawingMode(gc, kCGTextFillStroke);
	
        CGContextShowTextAtPoint(gc, x - pt.x / 2, y, str, strlen(str));
    }


    - (void)drawRect:(CGRect)rect{
	
        CGContextRef theContext = UIGraphicsGetCurrentContext();
        CGRect viewBounds = self.bounds;
	
        CGContextTranslateCTM(theContext, 0, viewBounds.size.height);
        CGContextScaleCTM(theContext, 1, -1);
	
        CGContextSelectFont (theContext, &quot;Helvetica&quot;, viewBounds.size.height,  kCGEncodingMacRoman);
	
        CGContextSetRGBFillColor (theContext, 1, 1, 1, 1);
        CGContextSetRGBStrokeColor (theContext, 0, 0, 0, 1);
        CGContextSetLineWidth(theContext, 1.0);
	
        ShowStringCentered(theContext, rect.size.width / 2.0, 12, [[self text] cStringUsingEncoding:NSASCIIStringEncoding]);
    }

I just have a nagging feeling that I&#39;m overlooking a simpler way to do this. Perhaps by overriding &quot;drawTextInRect&quot;, but I can&#39;t seem to get drawTextInRect to bend to my will at all despite staring at it intently and frowning really really hard.



How do I make UILabel display outlined text?

How would I store CGRect objects in a NSMutableArray, and then later retrieve them?

How to store CGRect values in NSMutableArray?

Does anybody know of any controls that will replicate the iOS7 style blur views. 

I&#39;m assumming there can be some kind of UIView subclass that will replicate the behavior. 

I&#39;m talking about these type views which blur the background extremely thickly so that they have pull effects from the background view. 


![enter image description here][1]


![][2]


  [1]: http://i.stack.imgur.com/MIYZa.jpg
  [2]: http://i.stack.imgur.com/iUzLc.jpg

iOS 7 style Blur view

I have a CGPoint called point that is being assigned a touch:

    UITouch *touch = [touches anyObject];
	
	CGPoint point = [touch locationInView:self];

I want to get the x coordinate value into my console log:

    NSLog(@&quot;x: %s&quot;, point.x);

When I use this, log output for this is:

x: (null)

I have verified that point is not null when this is called using the debugger and variable watch.

Any help appreciated,

Thanks // :)

NSLog with CGPoint data

I have three buttons in my view. After setting the cornerRadus in the viewDidLoad() : `button.layer.cornerRadius = 20` I get the following error message in the log:

     &lt;Error&gt;: CGContextSaveGState: invalid context 0x0. 
    If you want to see the backtrace, please set 
    CG_CONTEXT_SHOW_BACKTRACE environmental variable.


Questions: 

 - &lt;strike&gt;How can I set CG_CONTEXT_SHOW_BACKTRACE environmental variable?&lt;/strike&gt;
 - Or how can I fix this warning?

Okay I&#39;ve the backtrace now from the message. It doesn&#39;t make any sense to me. Some help please...

    Aug  7 14:27:00  &lt;Error&gt;: CGContextSaveGState: invalid context 0x0. Backtrace:
    	  &lt;-[UIStatusBarItemView updateContentsAndWidth]+33&gt;
    	   &lt;-[UIStatusBarItemView initWithItem:data:actions:style:]+477&gt;
    	    &lt;+[UIStatusBarItemView createViewForItem:withData:actions:foregroundStyle:]+134&gt;
    	     &lt;-[UIStatusBarLayoutManager _createViewForItem:withData:actions:]+163&gt;
    	      &lt;-[UIStatusBarLayoutManager _prepareEnabledItemType:withEnabledItems:withData:actions:itemAppearing:itemDisappearing:]+36
    	       &lt;-[UIStatusBarLayoutManager prepareEnabledItems:withData:actions:]+92&gt;
    	        &lt;-[UIStatusBarForegroundView _setStatusBarData:actions:animated:]+797&gt;
    	         &lt;-[UIStatusBarForegroundView setStatusBarData:actions:animated:]+332&gt;
    	          &lt;__51-[UIStatusBar _prepareToSetStyle:animation:forced:]_block_invoke+360&gt;
    	           &lt;+[UIView(Animation) performWithoutAnimation:]+65&gt;
    	            &lt;-[UIStatusBar _prepareToSetStyle:animation:forced:]+866&gt;
    	             &lt;-[UIStatusBar _requestStyleAttributes:animationParameters:forced:]+391&gt;
    	              &lt;-[UIStatusBar requestStyle:animationParameters:forced:]+437&gt;
    	               &lt;-[UIStatusBar requestStyle:animated:forced:]+90&gt;
    	                &lt;-[UIStatusBar _evaluateServerRegistration]+250&gt;
    	                 &lt;__45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke+590&gt;
    	                  &lt;-[UIView(Hierarchy) _postMovedFromSuperview:]+544&gt;
    	                   &lt;-[UIView(Internal) _addSubview:positioned:relativeTo:]+1967&gt;
    	                    &lt;-[UIStatusBarWindow setStatusBar:]+288&gt;
    	                     &lt;-[UIApplication _createStatusBarWithRequestedStyle:orientation:hidden:]+340&gt;
    	                      &lt;-[UIApplication _runWithMainScene:transitionContext:completion:]+950&gt;
    	                       &lt;-[UIApplication workspaceDidEndTransaction:]+188&gt;
    	                        &lt;-[FBSSerialQueue _performNext]+192&gt;
    	                         &lt;-[FBSSerialQueue _performNextFromRunLoopSource]+45&gt;
    	                          &lt;__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__+17&gt;
    	                           &lt;__CFRunLoopDoSources0+556&gt;
    	                            &lt;__CFRunLoopRun+867&gt;
    	                             &lt;CFRunLoopRunSpecific+488&gt;
    	                              &lt;-[UIApplication _run]+402&gt;
    	                               &lt;UIApplicationMain+171&gt;
    	                                &lt;main+117&gt;
    
    
    
    Aug  7 14:27:00  &lt;Error&gt;: CGContextTranslateCTM: invalid context 0x0. Backtrace:
    	  &lt;-[UIStatusBarItemView updateContentsAndWidth]+33&gt;
    	   &lt;-[UIStatusBarItemView initWithItem:data:actions:style:]+477&gt;
    	    &lt;+[UIStatusBarItemView createViewForItem:withData:actions:foregroundStyle:]+134&gt;
    	     &lt;-[UIStatusBarLayoutManager _createViewForItem:withData:actions:]+163&gt;
    	      &lt;-[UIStatusBarLayoutManager _prepareEnabledItemType:withEnabledItems:withData:actions:itemAppearing:itemDisappearing:]+36
    	       &lt;-[UIStatusBarLayoutManager prepareEnabledItems:withData:actions:]+92&gt;
    	        &lt;-[UIStatusBarForegroundView _setStatusBarData:actions:animated:]+797&gt;
    	         &lt;-[UIStatusBarForegroundView setStatusBarData:actions:animated:]+332&gt;
    	          &lt;__51-[UIStatusBar _prepareToSetStyle:animation:forced:]_block_invoke+360&gt;
    	           &lt;+[UIView(Animation) performWithoutAnimation:]+65&gt;
    	            &lt;-[UIStatusBar _prepareToSetStyle:animation:forced:]+866&gt;
    	             &lt;-[UIStatusBar _requestStyleAttributes:animationParameters:forced:]+391&gt;
    	              &lt;-[UIStatusBar requestStyle:animationParameters:forced:]+437&gt;
    	               &lt;-[UIStatusBar requestStyle:animated:forced:]+90&gt;
    	                &lt;-[UIStatusBar _evaluateServerRegistration]+250&gt;
    	                 &lt;__45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke+590&gt;
    	                  &lt;-[UIView(Hierarchy) _postMovedFromSuperview:]+544&gt;
    	                   &lt;-[UIView(Internal) _addSubview:positioned:relativeTo:]+1967&gt;
    	                    &lt;-[UIStatusBarWindow setStatusBar:]+288&gt;
    	                     &lt;-[UIApplication _createStatusBarWithRequestedStyle:orientation:hidden:]+340&gt;
    	                      &lt;-[UIApplication _runWithMainScene:transitionContext:completion:]+950&gt;
    	                       &lt;-[UIApplication workspaceDidEndTransaction:]+188&gt;
    	                        &lt;-[FBSSerialQueue _performNext]+192&gt;
    	                         &lt;-[FBSSerialQueue _performNextFromRunLoopSource]+45&gt;
    	                          &lt;__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__+17&gt;
    	                           &lt;__CFRunLoopDoSources0+556&gt;
    	                            &lt;__CFRunLoopRun+867&gt;
    	                             &lt;CFRunLoopRunSpecific+488&gt;
    	                              &lt;-[UIApplication _run]+402&gt;
    	                               &lt;UIApplicationMain+171&gt;
    	                                &lt;main+117&gt;
    
    
    
    
    Aug  7 14:27:00 &lt;Error&gt;: CGContextRestoreGState: invalid context 0x0. Backtrace:
    	  &lt;-[UIStatusBarItemView updateContentsAndWidth]+33&gt;
    	   &lt;-[UIStatusBarItemView initWithItem:data:actions:style:]+477&gt;
    	    &lt;+[UIStatusBarItemView createViewForItem:withData:actions:foregroundStyle:]+134&gt;
    	     &lt;-[UIStatusBarLayoutManager _createViewForItem:withData:actions:]+163&gt;
    	      &lt;-[UIStatusBarLayoutManager _prepareEnabledItemType:withEnabledItems:withData:actions:itemAppearing:itemDisappearing:]+36
    	       &lt;-[UIStatusBarLayoutManager prepareEnabledItems:withData:actions:]+92&gt;
    	        &lt;-[UIStatusBarForegroundView _setStatusBarData:actions:animated:]+797&gt;
    	         &lt;-[UIStatusBarForegroundView setStatusBarData:actions:animated:]+332&gt;
    	          &lt;__51-[UIStatusBar _prepareToSetStyle:animation:forced:]_block_invoke+360&gt;
    	           &lt;+[UIView(Animation) performWithoutAnimation:]+65&gt;
    	            &lt;-[UIStatusBar _prepareToSetStyle:animation:forced:]+866&gt;
    	             &lt;-[UIStatusBar _requestStyleAttributes:animationParameters:forced:]+391&gt;
    	              &lt;-[UIStatusBar requestStyle:animationParameters:forced:]+437&gt;
    	               &lt;-[UIStatusBar requestStyle:animated:forced:]+90&gt;
    	                &lt;-[UIStatusBar _evaluateServerRegistration]+250&gt;
    	                 &lt;__45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke+590&gt;
    	                  &lt;-[UIView(Hierarchy) _postMovedFromSuperview:]+544&gt;
    	                   &lt;-[UIView(Internal) _addSubview:positioned:relativeTo:]+1967&gt;
    	                    &lt;-[UIStatusBarWindow setStatusBar:]+288&gt;
    	                     &lt;-[UIApplication _createStatusBarWithRequestedStyle:orientation:hidden:]+340&gt;
    	                      &lt;-[UIApplication _runWithMainScene:transitionContext:completion:]+950&gt;
    	                       &lt;-[UIApplication workspaceDidEndTransaction:]+188&gt;
    	                        &lt;-[FBSSerialQueue _performNext]+192&gt;
    	                         &lt;-[FBSSerialQueue _performNextFromRunLoopSource]+45&gt;
    	                          &lt;__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__+17&gt;
    	                           &lt;__CFRunLoopDoSources0+556&gt;
    	                            &lt;__CFRunLoopRun+867&gt;
    	                             &lt;CFRunLoopRunSpecific+488&gt;
    	                              &lt;-[UIApplication _run]+402&gt;
    	                               &lt;UIApplicationMain+171&gt;
    	                                &lt;main+117&gt;




How can I set CG_CONTEXT_SHOW_BACKTRACE environmental variable?

I have the following CALayer:

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = CGRectMake(8, 57, 296, 30);
    gradient.cornerRadius = 3.0f;
    gradient.colors = [NSArray arrayWithObjects:(id)[RGB(130, 0, 140) CGColor], (id)[RGB(108, 0, 120) CGColor], nil];
    [self.layer insertSublayer:gradient atIndex:0];

I&#39;d like to add an **inner shadow** effect to it, but I am not quite sure how to do this. I suppose I would be required to draw in drawRect, however this would add the layer on top of other UIView objects, since it&#39;s supposed to be a bar behind some buttons, so I am at a loss as to what to do?

I could add another layer, but again, not sure how to achieve the inner shadow effect (like this:

![enter image description here][1]

Help appreciated...


  [1]: http://i.stack.imgur.com/MTFCR.png

Inner shadow effect on UIView layer?

There are a lot of resources about how to display a PDF in an App&#39;s `UIView`. What I am working on now is to create a PDF from `UIViews`. 

For example, I have a `UIView`, with subviews like Textviews, `UILabels`, `UIImages`, so how can I convert a **big** `UIView` as a whole including all its subviews and subsubviews to a PDF?

I have checked [Apple&#39;s iOS reference](https://developer.apple.com/library/archive/documentation/2DDrawing/Conceptual/DrawingPrintingiOS/GeneratingPDF/GeneratingPDF.html). However, it only talks about writing pieces of text/image to a PDF file.

The problem I am facing is that the content I want to write to a file as PDF is a lot. If I write them to the PDF piece by piece, it is going to be huge work to do.
That&#39;s why I am looking for a way to write `UIViews` to PDFs or even bitmaps.

I have tried the source code I copied from other Q/A within Stack Overflow. But it only gives me a blank PDF with the `UIView` bounds size.

    -(void)createPDFfromUIView:(UIView*)aView saveToDocumentsWithFileName:(NSString*)aFilename
    {
        // Creates a mutable data object for updating with binary data, like a byte array
        NSMutableData *pdfData = [NSMutableData data];
    	
        // Points the pdf converter to the mutable data object and to the UIView to be converted
        UIGraphicsBeginPDFContextToData(pdfData, aView.bounds, nil);
        UIGraphicsBeginPDFPage();
    	
        // draws rect to the view and thus this is captured by UIGraphicsBeginPDFContextToData
        [aView drawRect:aView.bounds];
    	
        // remove PDF rendering context
        UIGraphicsEndPDFContext();
    	
        // Retrieves the document directories from the iOS device
        NSArray* documentDirectories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);
    	
        NSString* documentDirectory = [documentDirectories objectAtIndex:0];
        NSString* documentDirectoryFilename = [documentDirectory stringByAppendingPathComponent:aFilename];
    	
        // instructs the mutable data object to write its context to a file on disk
        [pdfData writeToFile:documentDirectoryFilename atomically:YES];
        NSLog(@&quot;documentDirectoryFileName: %@&quot;,documentDirectoryFilename);
    }


How to Convert UIView to PDF within iOS?

Seen this asked before but my example does not seem to work.

    const CGFloat *toCol = CGColorGetComponents([[UIColor greenColor] CGColor]);

The array is empty from looking at it with GDB.  Any hints?

Extracting rgb from UIColor

How to get different lighter and darker variations of a given UIColor in Swift?

[![enter image description here][1]][1]


  [1]: http://i.stack.imgur.com/zVrrf.jpg

Get lighter and darker color variations for a given UIColor

I am attempting to draw a stroked circle by using a CAShapeLayer and setting a circular path on it.  However, this method is consistently less accurate when rendered to the screen than using borderRadius or drawing the path in a CGContextRef directly.

Here are the results of all three methods: ![enter image description here][1]

Notice that the third is poorly rendered, especially inside the stroke on the top and bottom. 

I **have** set the `contentsScale` property to `[UIScreen mainScreen].scale`.

Here is my drawing code for these three circles. What’s missing to make the CAShapeLayer draw smoothly?

    @interface BCViewController ()

    @end

    @interface BCDrawingView : UIView

    @end

    @implementation BCDrawingView

    - (id)initWithFrame:(CGRect)frame
    {
        if ((self = [super initWithFrame:frame])) {
            self.backgroundColor = nil;
            self.opaque = YES;
        }

        return self;
    }

    - (void)drawRect:(CGRect)rect
    {
        [super drawRect:rect];

        [[UIColor whiteColor] setFill];
        CGContextFillRect(UIGraphicsGetCurrentContext(), rect);

        CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(), NULL);
        [[UIColor redColor] setStroke];
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 1);
        [[UIBezierPath bezierPathWithOvalInRect:CGRectInset(self.bounds, 4, 4)] stroke];
    }

    @end

    @interface BCShapeView : UIView

    @end

    @implementation BCShapeView

    + (Class)layerClass
    {
        return [CAShapeLayer class];
    }

    - (id)initWithFrame:(CGRect)frame
    {
        if ((self = [super initWithFrame:frame])) {
            self.backgroundColor = nil;
            CAShapeLayer *layer = (id)self.layer;
            layer.lineWidth = 1;
            layer.fillColor = NULL;
            layer.path = [UIBezierPath bezierPathWithOvalInRect:CGRectInset(self.bounds, 4, 4)].CGPath;
            layer.strokeColor = [UIColor redColor].CGColor;
            layer.contentsScale = [UIScreen mainScreen].scale;
            layer.shouldRasterize = NO;
        }

        return self;
    }

    @end


    @implementation BCViewController

    - (void)viewDidLoad
    {
        [super viewDidLoad];

        UIView *borderView = [[UIView alloc] initWithFrame:CGRectMake(24, 104, 36, 36)];
        borderView.layer.borderColor = [UIColor redColor].CGColor;
        borderView.layer.borderWidth = 1;
        borderView.layer.cornerRadius = 18;
        [self.view addSubview:borderView];

        BCDrawingView *drawingView = [[BCDrawingView alloc] initWithFrame:CGRectMake(20, 40, 44, 44)];
        [self.view addSubview:drawingView];

        BCShapeView *shapeView = [[BCShapeView alloc] initWithFrame:CGRectMake(20, 160, 44, 44)];
        [self.view addSubview:shapeView];

        UILabel *borderLabel = [UILabel new];
        borderLabel.text = @&quot;CALayer borderRadius&quot;;
        [borderLabel sizeToFit];
        borderLabel.center = CGPointMake(borderView.center.x + 26 + borderLabel.bounds.size.width/2.0, borderView.center.y);
        [self.view addSubview:borderLabel];

        UILabel *drawingLabel = [UILabel new];
        drawingLabel.text = @&quot;drawRect: UIBezierPath&quot;;
        [drawingLabel sizeToFit];
        drawingLabel.center = CGPointMake(drawingView.center.x + 26 + drawingLabel.bounds.size.width/2.0, drawingView.center.y);
        [self.view addSubview:drawingLabel];

        UILabel *shapeLabel = [UILabel new];
        shapeLabel.text = @&quot;CAShapeLayer UIBezierPath&quot;;
        [shapeLabel sizeToFit];
        shapeLabel.center = CGPointMake(shapeView.center.x + 26 + shapeLabel.bounds.size.width/2.0, shapeView.center.y);
        [self.view addSubview:shapeLabel];
    }


    @end


EDIT: For those who cannot see the difference, I&#39;ve drawn circles on top of each other and zoomed in:

Here I&#39;ve drawn a red circle with `drawRect:`, and then drawn an identical circle with `drawRect:` again in green on top of it. Note the limited bleed of red. Both of these circles are &quot;smooth&quot; (and identical to the `cornerRadius` implementation):

![enter image description here][2]

In this second example, you&#39;ll see the issue. I&#39;ve drawn once using a `CAShapeLayer` in red, and again on top with a `drawRect:` implementation of the same path, but in green. Note that you can see a lot more inconsistency with more bleed from the red circle underneath. It&#39;s clearly being drawn in a different (and worse) fashion.

![enter image description here][3]


  [1]: http://i.stack.imgur.com/iYdyI.png
  [2]: http://i.stack.imgur.com/lpThN.png
  [3]: http://i.stack.imgur.com/2N1h0.png

How to draw a smooth circle with CAShapeLayer and UIBezierPath?

in my iPad app, I&#39;d like to make a screenshot of a UIView taking a big part of the screen. Unfortunately, the subviews are pretty deeply nested, so it takes to long to make the screenshot and animate a page curling afterwards.

Is there a faster way than the &quot;usual&quot; one?

    UIGraphicsBeginImageContext(self.bounds.size);
    [self.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

If possible, I&#39;d like to avoid caching or restructuring my view.


iOS: what&#39;s the fastest, most performant way to make a screenshot programmatically?

I need to scale down an image, but in a sharp way. In Photoshop for example there are the image size reduction options &quot;Bicubic Smoother&quot; (blurry) and &quot;Bicubic Sharper&quot;.

Is this image downscaling algorithm open sourced or documented somewhere or does the SDK offer methods to do this?

How to scale down a UIImage and make it crispy / sharp at the same time instead of blurry?

I wonder if someone can distinguish precisely between these?
For my understanding, Core Graphics is just a &quot;Framework Package&quot; which contains Quartz Core and Quartz 2D. But I&#39;m not sure about if Quartz 2D actually is Quartz Core? Maybe someone can draw some lines there? What makes up the differences between these?

When looking at the documentation, I see Quartz Core is listing up all the Core Animation stuff only. So Quartz Core == Core Animation?

What&#39;s the difference between Quartz Core, Core Graphics and Quartz 2D?

I have a series of user-customized images within an iOS app that are being animated in a simple, frame-by-frame flip book style.  

My question is this: is there a way to allow users to export their animation as an animated gif?  Ideally, I&#39;d like to enable them to email, social share (T/FB) or (worst case..) save an animated gif to their documents folder for retrieval via iTunes.   

I know how to save a .png to the photo library, and I found a way to record an animation as a QT file (http://www.cimgf.com/2009/02/03/record-your-core-animation-animation/), but I haven&#39;t found a way to just kick out a plain old animated gif.  Am I missing something in Core Animation or somewhere else? Are there any approaches, frameworks, or resources that anyone can recommend?  Sorry if the question is too general - struggling to find a starting point.


Create and export an animated gif via iOS?

I&#39;ve been trying to figure out a way to draw segments as illustrated in the following image:

![enter image description here][1]

I&#39;d like to:

 1. draw the segment
 2. include gradients
 3. include shadows
 4. animate the drawing from 0 to n angle

I&#39;ve been attempting to do this with `CGContextAddArc` and similar calls but not getting very far.

Can anyone help ?


  [1]: http://i.stack.imgur.com/oadFr.png

Draw segments from a circle or donut

I&#39;m trying to get `CIImage` from ImageView that display on the screen. 

    UIImage *image = myImageView.image;

convert image `UIImage` to `CIImage`.

    CIImage *cImage = [....];

How to do this? 

How to Convert UIImage to CIImage and vice versa

I&#39;m trying to draw a shadow under the bottom edge of a `UIView` in Cocoa Touch. I understand that I should use `CGContextSetShadow()` to draw the shadow, but the Quartz 2D programming guide is a little vague:

 1. Save the graphics state.
 2. Call the function `CGContextSetShadow`, passing the appropriate values.
 3. Perform all the drawing to which you want to apply shadows.
 4. Restore the graphics state

I&#39;ve tried the following in a `UIView` subclass:

    - (void)drawRect:(CGRect)rect {
        CGContextRef currentContext = UIGraphicsGetCurrentContext();
        CGContextSaveGState(currentContext);
        CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);
        CGContextRestoreGState(currentContext);
        [super drawRect: rect];
    }

..but this doesn&#39;t work for me and I&#39;m a bit stuck about (a) where to go next and (b) if there&#39;s anything I need to do to my `UIView` to make this work?

How do I draw a shadow under a UIView?

We&#39;re making a user-space device driver for OS X that moves the cursor using Quartz Events, and we ran into a problem when games — especially ones that run in a windowed mode — can&#39;t properly capture the mouse pointer *(= contain/keep it within the boundaries of their windows)*. For example, it would go outside the game window and click on the desktop or nearby inactive applications.

We could fix this if only we could detect when an active application calls CGAssociateMouseAndMouseCursorPosition.

How would you do this? Any ideas are appreciated.

Detecting CGAssociateMouseAndMouseCursorPosition

I have a `UIScrollView` decendent that implements a takeScreenshot method that looks like this:


    -(void)takeScreenshot {  
      CGRect contextRect  = CGRectMake(0, 0, 768, 1004);
      UIGraphicsBeginImageContext(contextRect.size);	
      [self.layer renderInContext:UIGraphicsGetCurrentContext()];
      UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
      UIGraphicsEndImageContext();
      
      // do something with the viewImage here.
    }

This basically moves to the top of the scroll view, and takes a screenshot of the visible area. It works fine when the iPad is oriented portrait, but when it&#39;s in landscape the bottom of the image is cut off (as the height of the visible area is only 748, not 1004).

Is it possible to get a snapshot of the `UIScrollView`, including areas not on screen? Or do I need to scroll the view down, take a second photo and stitch them together?

All Core Graphics Solutions on Gang of Coders

Total of 37 Core Graphics Solutions