cgcontext

问题 I have a UIView that draws a circle inside it using the following code: -(void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetFillColorWithColor(context, myColor); CGContextFillEllipseInRest(context, myRect); } I want to animate this circle to a grey color... How can I achieve this? -(void)fadeToGrey { // What goes here? } 回答1: You should use CAShapeLayer as a layer class and do your drawing inside setLayerProperties: method. drawRect: will not be

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 I try to add a CAGradient effect in a pie chart I make with Core Graphics. It turns out I am not able and certainly not understand very well how to apply it to a view that is part of a CGPath... override func draw(_ rect: CGRect) { ... func arc(myRadius: CGFloat, myStartAngle: CGFloat, myEndAngle: CGFloat) { // This is the pie chart segment context?.setFillColor(phenotypeColor.cgColor) context?.move(to: center) context?.addArc(center: center, radius: finalRadius, startAngle: myStartAngle,

问题 I am trying to draw an image with a 2px transparent border: CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 0.0); CGContextAddRect(context, CGRectMake(0.0, 0.0, outputImageSize.width, outputImageSize.height)); CGContextDrawPath(context, kCGPathFill); [image drawInRect:CGRectMake(2.0, ((outputImageSize.height - userPhotoImageSize.height) / 2.0) +2.0, userPhotoImageSize.width -4.0, userPhotoImageSize.height -4.0)]; UIImage *screenshot =

问题 I wrote the following code in ViewDidLoad // Implement viewDidLoad to do additional setup after loading the view, typically from a nib. -(void)viewDidLoad { [super viewDidLoad]; NSString *str = [NSString stringWithFormat:@"Veer"]; CGColorSpaceRef rgbColorspace = CGColorSpaceCreateDeviceRGB(); CGFloat values[4] = {55.0, 0.0, 0.0, 1.0}; CGColorRef glowColor = CGColorCreate(rgbColorspace, values); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetShadowWithColor( context,

问题 (UIImage *) cropToSquare:(UIImage *)_image { if(_image.size.height < _image.size.width) { CGRect drawRect = CGRectMake(0, 0, _image.size.height, _image.size.height); UIGraphicsBeginImageContext(drawRect.size); CGContextRef currentContext = UIGraphicsGetCurrentContext(); CGRect cropArea = CGRectMake (((_image.size.width - _image.size.height)/2), 0, _image.size.height, _image.size.height); CGContextTranslateCTM(currentContext, 0.0, _image.size.height); CGContextScaleCTM(currentContext, 1.0, -1

问题 I have an area where a user can add their signature to an app, to verify an order. They sign with their touch. The only thing is, the frame for the signature is large, and if the user were to make a signature very small, when I save the image, I'm left with a wealth of empty space around the image, which, when I add it to an email further down the process can look horrible. Is there any way, using that I can crop the image to whatever the bounds of the actual content is, and not the bounds of

问题 I'm trying to save all of the contents of a UIScrollView to a .pdf. I found some tutorials for saving the current view, and they all rely on creating a CGContextRef using UIGraphicsGetCurrentContext() . Right now, I capture my view with just CGContextRef context = UIGraphicsGetCurrentContext(); [myView.layer renderInContext:context]; And that works fine for a plain UIView. However, when I try to pass a UIScrollView as myView , it passes the visible part of the UIScrollView fine, but anything

问题 I'm creating many colour variations of an image using Core Graphics. I need to create about 320 in total but gradually, the memory usage of the app keeps increasing until it crashes. From Instruments, I see that more CGImage objects are being created and stay alive. I want to release them because I store the images to the cache directory in PNG format. I have searched through all other solutions I could find without success. Any help is appreciated. Thanks. Here's the main part: +(UIImage *

问题 I have the following code for a custom view. @IBDesignable class SplitCircleView: UIView { override init(frame: CGRect) { super.init(frame: frame) draw(frame) } required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) draw(frame) } override func draw(_ rect: CGRect) { self.backgroundColor = .clear drawSlice(rect: self.frame, startPercent: 87.5, endPercent: 37.5, color: .green) drawSlice(rect: self.frame, startPercent: 37.5, endPercent: 87.5, color: .red) } func drawSlice(rect: