core-graphics

问题 I needed to draw a shadow around photos of users. I drew those circle photos by drawing a circle and then clipping the context. Here's the snippet of my code: + (UIImage*)roundImage:(UIImage*)img imageView:(UIImageView*)imageView withShadow:(BOOL)shadow { UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, NO, [UIScreen mainScreen].scale); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextAddEllipseInRect(context, CGRectMake(0,0, imageView.width, imageView.height));

问题 I am working on a drawing application, I am drawing into CGlayers , I am creating a CGlayer this way -(void)drawRect { if(self.DrawingLayer == nil) { CGFloat scale = self.contentScaleFactor; CGRect bounds = CGRectMake(0, 0, self.bounds.size.width * scale, self.bounds.size.height * scale); CGLayerRef layer = CGLayerCreateWithContext(context, bounds.size, NULL); CGContextRef layerContext = CGLayerGetContext(layer); CGContextScaleCTM(layerContext, scale, scale); self.DrawingLayer = layer; }

问题 I have created a core text view and visually it's working great but i run it for 30 minutes with a lot of data coming in and it crashes. The debugger starts saying 'received memory warning'. I think the views i'm drawing that refresh on every new line that comes in from telnet, are not leaving memory on a redraw completely. code below. The first part of this code might be an issue. I found on a redraw i had to clear the old views or it over layed or drew on top and text got garbled. But it

问题 I have this code so far: CGPoint midLeft = CGPointMake(0, additionalHeight); CGPoint bottomCenter = CGPointMake(self.bounds.size.width / 2, self.bounds.size.height); CGPoint midRight = CGPointMake(self.bounds.size.width, additionalHeight); CGPoint topRight = CGPointMake(self.bounds.size.width, 0); CGPoint topLeft = CGPointMake(0, 0); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextMoveToPoint(context, midLeft.x, midLeft.y); CGContextAddLineToPoint(context, midRight.x, midRight

问题 I'm trying to set a transparent background for a CGContext but keep getting : CGBitmapContextCreateImage: invalid context 0x0 Here's what I've got. If I switch kCGImageAlphaLast to kCGImageAlphaNoneSkipFirst it works but the alpha channel is completely ignored. I'm very new to this color & context stuff - any ideas? -(BOOL) initContext:(CGSize)size { int bitmapByteCount; int bitmapBytesPerRow; bitmapBytesPerRow = (size.width * 4); bitmapByteCount = (bitmapBytesPerRow * size.height);

问题 I want to pre-render some graphics into CGLayer for fast drawing in future. I found that CGLayerCreateWithContext requires a CGContext parameter. It can be easily found in drawRect: method. But I need to create a CGLayer outside of drawRect: . Where should I get CGContext ? Should I simply create temporary CGBitmapContext and use it? UPDATE: I need to create CGLayer outside of drawRect: because I want to initialize CGLayer before it is rendered. It is possible to init once on first drawRect

问题 Is it possible to change how radius of the grouped UITableView? The rounded corners are way to drastic for my design. 回答1: I believe that the only way to do this is to provide your own background images for your table cells. You can provide 3 images to have a rounded feel to the UITableView like Apple Does. in - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath set the cell's backgroundView to a UIView with the image you want based on the

问题 I am building an app that takes a few different text files and strings them together, then builds a pdf out of them. I needed to add the file's text add separate times so I can add in hyperlinks to the text from each file. I have made some progress and got it to display almost accurately, but it appears CTFramesetterCreateWithAttributedString is not sizing correctly. For example, the first of the three files displays too much, in other words, after the text ends there is a blank page that

问题 I'm trying to figure out how to save a CGImageRef as JPEG2000. At the moment I get scattered-looking image output. I have the following code which works for every other format except kUTTypeJPEG2000. Saving as kUTTypeGIF or kUTTypePNG works fine. Interesting, saving as kUTTypeJPEG2000 without an alpha channel works too. How can I get the image to output correctly? - (void)saveImage:(CGImageRef)image path:(NSString *)path { // Set the image compression quality CFMutableDictionaryRef properties

问题 I have a fairly standard RGBA image as a CGImageRef. I'm looking to convert this into a GraphicsMagick Blob (http://www.graphicsmagick.org/Magick++/Image.html#blobs) What's the best way to go about transposing it? I have this but it produces only a plain black image if I specify PNG8 in the pathString or it crashes: - (void)saveImage:(CGImageRef)image path:(NSString *)pathString { CGDataProviderRef dataProvider = CGImageGetDataProvider(image); NSData *data = CFBridgingRelease