cgcontext

问题 does anybody know what to do with this problem: my image in a custom MKPolygonView is flipped upside down? The idea (this is working OK already) is having an class "SnowmapsOverlayView" that extends "MKPolygonView", that displays a image. This image has a default location & size on the map (acts as a GroundOverlay in the Google Maps web API). This is all working fine, but the image is displayed upside down. I've tryed the following options, but with no result: CGContextDrawImage draws image

问题 This question already has answers here : Cannot create PDF document with 400+ pages on iOS (4 answers) Closed 3 years ago . I need to generate PDF more than 60 pages and need to Print it, but in iPhone & iPad memory Ram raises to 350.50MB-500.00MB and Crashes . For Reducing memory->Running in dispatch queues also that doesn't help Can't find the solution for this . Plz help me in this ... and referred below link but doesn't help Cannot create PDF document with 400+ pages on iOS -(NSData*

问题 I'm applying filter on UIImage but after conversion, it appear as sideway. Below is my code. CIImage *ciImage = [[CIImage alloc] initWithImage:self.imgToProcess]; CIFilter *filter = [CIFilter filterWithName:@"CIPhotoEffectChrome" keysAndValues:kCIInputImageKey, ciImage, nil]; [filter setDefaults]; CIContext *context = [CIContext contextWithOptions:nil]; CIImage *outputImage = [filter outputImage]; CGImageRef cgImage = [context createCGImage:outputImage fromRect:[outputImage extent]]; UIImage

问题 I am using two CGlayers for drawing, Layer1 and Layer2, I draw into Layer1 and on touches end, I transfer the data into Layer2 and just clear Layer1, and in my drawRect, method, I draw both layers to context. On erase button clicked, I transfer the drawing from Layer2 to Layer1 and then I erase layer1, but on touches end, I dont transfer it to Layer2, because I only erase Layer1 On pen clicked If erase has happened, I transfer drawing from Layer1 to Layer2, otherwise previous drawing can

问题 I want to stroke a CGContext path using three or four images, but randomly cycle through the images as I'm drawing the path. I want to draw the images INSTEAD!! of drawing the CGContext I am now. I have this code so far - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; CGPoint currentPoint = [touch locationInView:self.view]; currentPoint.x = currentPoint.x; currentPoint.y = currentPoint.y; mouseSwiped = YES; UIGraphicsBeginImageContext

问题 Those two functions are currently my bottleneck. I am working with very large bitmaps. How can I improve their performance? 回答1: You could cache smaller versions of your bitmaps which you create before drawing the first time and then simply draw the downscaled samples instead of the full-blown 15 megapixel stuff. Then again make sure you are only drawing what is necessary i.e. in 'drawRect: (NSRect) rect' only draw inside the rect (unless absolutely necessary). And try not do perform drawings

问题 I'm trying to draw some text on the iPhone, but in landscape mode, where the home button is on the left. So I need to somehow twist the numbers (I'm guessing I use a transform) ? Here's what I have now: CGContextSetRGBFillColor(context, 1.0, 0, 0, 1.0); CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0); CGContextSelectFont(context, "Helvetica", 20, kCGEncodingMacRoman); CGContextSetTextMatrix(context, CGAffineTransformMakeRotation(M_PI/2)); CGContextSetTextDrawingMode(context,

问题 I'd like to take a UITextView and allow the user to enter text into it and then trigger a copy of the contents onto a quartz bitmap context. Does anyone know how I can perform this copy action? Should I override the drawRect method and call [super drawRect] and then take the resulting context and copy it? If so, does anyone have any reference to sample code to copy from one context to another? Update: from reading the link in the answer below, I put together this much to attempt to copy my

问题 New programmer here. I am having issues trying to use Core Graphics to draw a stroked arc around my touch location. I have the method to draw the circle working fine, and I have tested and am registering touches when I tap the screen, but when I try to call the method to draw the circle when I tap, I get the error "CGContextBlahBlah: invalid context 0x0" I think that this is because I'm not calling the method in drawRect:(). So how am I able to call this method on a touch? Furthermore, how

问题 I am trying to create a 8-bit grayscale context as follows : CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); CGContextRef context = CGBitmapContextCreate( data, m_width, m_height, 8, m_width, colorSpace, kCGBitmapByteOrder32Little|kCGImageAlphaNone); But I have the following error : CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 8 bits/pixel; 1-component color space; kCGImageAlphaNone; 1936 bytes/row. Why is this combination unsupported ? 回答1: