core-graphics

问题 I am working on a circular progress bar for custom game center achievements view and I have kind of "hit the wall". I am struggling with this for over two hours and still cannot get it to work. The thing is, that I need a circular progress bar, where I would be able to set (at least) the track(fill) image. Because my progress fill is a rainbow like gradient and I am not able to achieve the same results using only code. I was messing with CALayers, and drawRect method, however I wasn't

问题 After updating my iPad (mini) to iOS7 I experienced that my drawing app is lagging and crashing after a few strokes. Now, when I run the app with Instruments/memory allocation tool in xcode 5, I see that the VM: CG raster data category is filling up rapidly when drawing on the screen. There seems to be a multitude of CGDataProviderCreateWithCopyOfData calls being made, each 3.00Mb in size. After continous drawing the app receives memory warnings, and usually terminates. The code basically

问题 I need to draw an hexagon and fill it with a color build with an Image as pattern. I did: CGContextSaveGState(context); CGContextSetLineCap(context, kCGLineCapRound); CGContextSetFillColorWithColor(context, [[UIColor colorWithPatternImage:[UIImage imageNamed:@"patternerba.png"]] CGColor]); CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]); CGContextSetLineWidth(context, 3.0); // drawing hexagon here... CGContextStrokePath(context); CGContextFillPath(context); [

问题 I need to draw an hexagon and fill it with a color build with an Image as pattern. I did: CGContextSaveGState(context); CGContextSetLineCap(context, kCGLineCapRound); CGContextSetFillColorWithColor(context, [[UIColor colorWithPatternImage:[UIImage imageNamed:@"patternerba.png"]] CGColor]); CGContextSetStrokeColorWithColor(context, [[UIColor blackColor] CGColor]); CGContextSetLineWidth(context, 3.0); // drawing hexagon here... CGContextStrokePath(context); CGContextFillPath(context); [

问题 I am working on an iOS project that loads UIImages from URLs in a background thread and displays them in a horizontally paged scroll view. This behavior should mimic that of the native photo library application for iPhone. I have everything setup in a way that I believe should work, but upon drawing the UIImages in the main UI graphics context, I occasionally see this message print out in the console: ImageIO: <ERROR> CGImageReadSessionGetCachedImageBlockData ***

问题 You can use the following code to draw an arc using Quartz: CGContextMoveToPoint(context2, x, y); CGContextAddArcToPoint(context2, x1, y1, x2, y2, r); In these functions, (x,y) is the starting point and r is the arc radius but what are (x1,y1) and (x2,y2) ? 回答1: http://developer.apple.com/library/ios/documentation/GraphicsImaging/Reference/CGContext/Reference/reference.html#//apple_ref/c/func/CGContextAddArcToPoint x1 : The x-value, in user space coordinates, for the end point of the first

问题 ((UIImageView*)[dsry objectAtIndex:0]).transform = CGAffineTransformMakeRotation(1.57*2); ((UIImageView*)[dsry objectAtIndex:0]).transform = CGAffineTransformMakeScale(.5,.5); Just one of these works at a time. How can I save a transformation and then apply another? Cheers 回答1: To expand upon what Peter said, you would want to use code like the following: CGAffineTransform newTransform; newTransform = CGAffineTransformMakeRotation(1.57*2); ((UIImageView*)[dsry objectAtIndex:0]).transform =

问题 Actually, I thought that there would be an easy way to achieve that. What I need is pure alpha value information. For testing, I have a 50 x 55 px PNG, where on every edge a 5x5 pixel rectangle is fully transparent. In these areas alpha has to be 0.Everywhere else it has to be 255. I made very sure that my PNG is created correctly, and it also looks correctly. Please tell me if this is theoretically correct: I created an CGImageRef that has only the alpha channel and nothing else. This is

问题 I am having this very strange issue. I am creating animated gifs from UIImages and most of the time they come out correct. However when I start to get into larger size images my colors start to disappear. For example if I do a 4 frame 32 x 32 pixel image with no more than 10 colors no issue. If I scale the same image up to 832 x 832 I lose a pink color and my brown turns green. @1x 32 x 32 @10x 320 x 320 @26x 832 x 832 Here is the code I use to create the gif... var kFrameCount = 0 for

问题 I'm overriding drawRect: in one of my views and it works even without calling [super drawrect:rect]. How does that work? - (void)drawRect:(CGRect)rect{ CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetBlendMode(context, kCGBlendModeDestinationOver); [[UIColor clearColor] setFill]; UIRectFill(CGRectMake(0,0,100,100)); } 回答1: From the documentation: "The default implementation of this method does nothing.Subclasses that use technologies such as Core Graphics and UIKit to draw