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  • Why there is an invalid context error?

    - by Tattat
    Here is the code I use to draw: - (void) drawSomething { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetRGBStrokeColor(context, 1, 0, 0, 1); CGContextSetLineWidth(context, 6.0); CGContextMoveToPoint(context, 100.0f, 100.0f); CGContextAddLineToPoint(context, 200.0f, 200.0f); CGContextStrokePath(context); NSLog(@"draw"); } But I got the error like this: [Session started at 2010-04-03 17:51:07 +0800.] Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextSetRGBStrokeColor: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextSetLineWidth: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextMoveToPoint: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextAddLineToPoint: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextDrawPath: invalid context Why it prompt me to say that the context is invalided?

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  • Drawing CGPathRef in ScrollView using Iphone sdk.

    - by Ann
    Hi all. I want to draw some curve in my scroll view using CGPathRef. I tried to draw this path but i see only the part of my CGPathRef which located at 320x480 pixels. Is it way to do that. Thank you in advance. Here is my code path = CGPathCreateMutable(); CGContextBeginPath(ctx); CGContextMoveToPoint(ctx, [[pathArray objectAtIndex:0]CGPointValue].x,[[pathArray objectAtIndex:0]CGPointValue].y ); for(int i = 1; i < [pathArray count]; ++i) { CGContextAddLineToPoint(ctx, [[pathArray objectAtIndex:i]CGPointValue].x, [[pathArray objectAtIndex:i]CGPointValue].y); } CGContextClosePath(ctx); CGContextSetRGBFillColor(ctx, 0.5, 0.3, 0.2, 0.5); CGContextFillPath(ctx); And when I scroll my view the line does not change its location. My goal is to move this line during scrolling.

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  • correct fisheye distortion

    - by Will
    I have some points that describe positions in a picture taken with a fisheye lens. I've found this description of how to generate a fisheye effect, but not how to reverse it. How do you calculate the radial distance from the centre to go from fisheye to rectilinear? My function stub looks like this: Point correct_fisheye(const Point& p,const Size& img) { // to polar const Point centre = {img.width/2,img.height/2}; const Point rel = {p.x-centre.x,p.y-centre.y}; const double theta = atan2(rel.y,rel.x); double R = sqrt((rel.x*rel.x)+(rel.y*rel.y)); // fisheye undistortion in here please //... change R ... // back to rectangular const Point ret = Point(centre.x+R*cos(theta),centre.y+R*sin(theta)); fprintf(stderr,"(%d,%d) in (%d,%d) = %f,%f = (%d,%d)\n",p.x,p.y,img.width,img.height,theta,R,ret.x,ret.y); return ret; }

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  • For "draggable" div tags that are NOT nested: JQuery/JavaScript div tag “containment” approach/algor

    - by Pete Alvin
    Background: I've created an online circuit design application where .draggable() div tags are containers that contain smaller div containers and so forth. Question: For any particular div tag I need to quickly identify if it contains other div tags (that may in turn contain other div tags). -- Since the div tags are draggable, in the DOM they are NOT nested inside each other but I think are absolutely positioned. So I think that a "hit testing" approach is the only way to determine containment, unless there is some "secret" routine built-in somewhere that could help with this. I've searched JQuery and I don't see any built-in routine for this. Does anyone know of an algorithm that's quicker than O(n^2)? Seems like I have to walk the list of div tags in an outer loop (n) and have an inner loop (another n) to compare against all other div tags and do a "containment test" (position, width, height), building a list of contained div tags. That's n-squared. Then I have to build a list of all nested div tags by concatenating contained lists. So the total would be O(n^2)+n. There must be a better way?

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  • CGPath and Quartz 2D

    - by iphonedevnoob
    I want to create a triangle using Quartz 2D functions. The 3 edges of the triangle should be in different colors. I am able to create the triangle but not able to set the color of each edge or subpath separately. Any suggestions or sample code are much appreciated.

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  • Building a clip area in a UIView from path objects in its subviews

    - by hkatz
    I'm trying to produce a clipping area in a UIView that's generated from path objects in its subviews. For example, I might have one subview containing a square and another containing a circle. I want to be able to produce a clip in the parent superview that's the union of both these shapes. Can someone explain how to do this? About all I've been able to figure out so far is that: 1 - the superview's drawRect: method is called before its subviews' drawRects are, and 2 - the ContextRef that's accessible in all three instances is the same. Other than that I'm stumped. Thanks, Howard

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  • Soft Paint Bucket Fill: Colour Equality

    - by Bart van Heukelom
    I'm making a small app where children can fill preset illustrations with colours. I've succesfully implemented an MS-paint style paint bucket using the flood fill argorithm. However, near the edges of image elements pixels are left unfilled, because the lines are anti-aliased. This is because the current condition on whether to fill is colourAtCurrentPixel == colourToReplace (the colours are RGB uints) I'd like to add a smoothing/treshold option like in Photoshop and other sophisticated tools, but what's the algorithm to determine the equality/distance between two colours? if (match(pixel(x,y), colourToReplace) setpixel(x,y,colourToReplaceWith) How to fill in match()? Here's my current full code: var b:BitmapData = settings.background; b.lock(); var from:uint = b.getPixel(x,y); var q:Array = []; var xx:int; var yy:int; var w:int = b.width; var h:int = b.height; q.push(y*w + x); while (q.length != 0) { var xy:int = q.shift(); xx = xy % w; yy = (xy - xx) / w; if (b.getPixel(xx,yy) == from) { b.setPixel(xx,yy,to); if (xx != 0) q.push(xy-1); if (xx != w-1) q.push(xy+1); if (yy != 0) q.push(xy-w); if (yy != h-1) q.push(xy+w); } } b.unlock(null);

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  • How to write text(using CGContextShowTextAtPoint) dynamically near graph x and y-axis intervals?

    - by Rajendra Bhole
    I developed graph using NSObject class and using CGContext method. The following code displaying dynamically in X and Y-axis intervals, CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextSetLineWidth(ctx, 2.0); CGContextMoveToPoint(ctx, 30.0, 200.0); CGContextAddLineToPoint(ctx, 30.0, 440.0); for(float y = 400.0; y >= 200.0; y-=30) { CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextMoveToPoint(ctx, 28, y); CGContextAddLineToPoint(ctx, 32, y); CGContextStrokePath(ctx); //CGContextClosePath(ctx); } CGContextMoveToPoint(ctx, 10, 420.0); CGContextAddLineToPoint(ctx, 320, 420.0); //CGContextAddLineToPoint(ctx, 320.0, 420.0); //CGContextStrokePath(ctx); for(float x = 60.0; x <= 260.0; x+=30) { CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextMoveToPoint(ctx, x, 418.0); CGContextAddLineToPoint(ctx, x, 422.0); CGContextStrokePath(ctx); CGContextClosePath(ctx); } I want to write the dynamic text on the X and Y-axis lines near the intervals (like X-axis is denoting number of days per week and Y-axis denoting something per someting)? Thanks.

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  • Metric 3d reconstruction

    - by srand
    I'm trying to reconstruct 3D points from 2D image correspondences. My camera is calibrated. The test images are of a checkered cube and correspondences are hand picked. Radial distortion is removed. After triangulation the construction seems to be wrong however. The X and Y values seem to be correct, but the Z values are about the same and do not differentiate along the cube. The 3D points look like as if the points were flattened along the Z-axis. What is going wrong in the Z values? Do the points need to be normalized or changed from image coordinates at any point, say before the fundamental matrix is computed? (If this is too vague I can explain my general process or elaborate on parts)

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  • iPhone - Is it ok to override UITableViewCell setSelected:animated

    - by Brian
    I am drawing custom UITableViewCells. My cells are opaque and are completely drawn in the drawRect of the cell to help with performance. I want to handle the look of a selected cell myself. If I don't, then the contents of my cell is covered up by the selectedBackgroundView that is added. Is it common or acceptable to override the setSelected:animated method of my cell so this is done properly. I guess if I did that, then I would not call the super's setSelected method since I would be handling how the cell will show that its selected. I would also have to set the selected property of the cell. Any help would be great. Thanks.

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  • How do I translate a point from one rect to a point in a scaled rect?

    - by Bill
    I have an image (i) that's been scaled from its original size (rectLarge) to fit a smaller rectangle (rectSmall). Given a point p in rectSmall, how can I translate this to a point in rectLarge. To make this concrete, suppose I have a 20x20 image that's been scaled to a 10x10 rect. The point (1, 1) in the smaller rect should be scaled up to a point in the larger rect (i.e. (2,2)). I'm trying to achieve this with: result.x = point.x * (destRect.size.width / srcRect.size.width ); result.y = point.y * (destRect.size.height / srcRect.size.height); However, the points generated by this code are not correct - they do not map to the appropriate point in the original image. What am I doing wrong?

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  • How do bezier handles work?

    - by user146780
    On Wikipedia I found information about bezier curves and made a function to generate the inbetween points for a bezier polygon. I noticed that Expression Design uses bezier handles. This allows a circle to be made with 4 points each with a bezier handle. I'm just not sure mathematically how this works in relation with the formula for bezier point at time T. How do these handle vectors work to modify the shape? Basically what's there relation to the bezier formula? Thanks

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  • iPhone image distortion

    - by Corey Floyd
    Are there any reasons why the simulator will display UIImageViews properly, but incorrectly on the iPhone? My Process: An image in a PNG file Start a UIGraphicsBeginImageContext() Draw the PNG in a CGrect Draw text in the CGRect Create an UIImage from the context Set the image of a UIImaveView to the UIImage Set the frame of the UIImageView to the size of the PNG Add as a subview Outcome: The image does not display correctly. The rightmost 1-3 pixels of the image is just a vertical white line. This occurs only on the device and not on the simulator. I can fix the problem, but only by increasing the size of the UIImageView. If I increase the size.height of the UIImageView by 1 pixel, it displays the UIImage correctly. Of course, these leaves the iPhone to scale my image before drawing it on screen which is not desirable. Any ideas why this occurs or any fixes for it? (I will post my code if needed)

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  • Odd values/movement with UITouch and CGPoint.

    - by Joshua
    I'm getting odd numbers from UITouch and CGPoint and one is different, I also think this maybe causing a flickering affect in my app when I try to move something by following a touch. This is the code I'm using: - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { NSLog(@"touchDown"); UITouch *touch = [touches anyObject]; firstTouch = [touch locationInView:self.view]; if (CGRectContainsPoint(but.frame, firstTouch)) { butContains = YES; NSLog(@"butContains = %d", butContains); } } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; currentTouch = [touch locationInView:self.view]; NSInteger x = currentTouch.x; NSInteger y = currentTouch.y; CGFloat CGX = (CGFloat)x; CGFloat CGY = (CGFloat)y; if (butContains == YES) { NSLog(@"touch in subView/contentView"); sub.frame = CGRectMake(CGX, CGY, 130.0, 21.0); } NSLog(@"touch moved"); } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; currentTouch = [touch locationInView:self.view]; NSLog(@"User tapped at %@", NSStringFromCGPoint(currentTouch)); NSLog(@"Point %a, %a", currentTouch.x, currentTouch.y); NSInteger x = currentTouch.x; NSInteger y = currentTouch.y; NSLog(@"Point %a, %a", y, x); CGFloat CGX = (CGFloat)x; CGFloat CGY = (CGFloat)y; NSLog(@"Point %g, %g", CGX, CGY); if (butContains == YES) { NSLog(@"touch in subView/contentView"); sub.frame = CGRectMake(CGX, CGY, 130.0, 21.0); } butContains = NO; NSLog(@"touch ended"); } - (IBAction)add:(id)sender{ InSightViewController *contentView = [[InSightViewController alloc] initWithNibName:@"SubView" bundle:[NSBundle mainBundle]]; [contentView loadView]; [self.view insertSubview:contentView.view atIndex:0]; } This is what I get from the touchesEnded method in the Debugger. 2010-04-20 20:06:13.045 InSight[25042:207] User tapped at {50, 78} 2010-04-20 20:06:13.047 InSight[25042:207] Point 0x1.9p+5, 0x1.38p+6 2010-04-20 20:06:13.048 InSight[25042:207] Point 0x1.900000027p-1037, 0x1.38p+6 2010-04-20 20:06:13.048 InSight[25042:207] Point 50, 78 And this is what's happening in the Simulator. fwdr.org/file:y8bd As this is a complicated problem this is the source code of my XCode Project aswell. http://cl.ly/Qjj

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  • How to read and modify the colorspace of an image in c#

    - by Matthias
    I'm loading a Bitmap from a jpg file. If the image is not 24bit RGB, I'd like to convert it. The conversion should be fairly fast. The images I'm loading are up to huge (9000*9000 pixel with a compressed size of 40-50MB). How can this be done? Btw: I don't want to use any external libraries if possible. But if you know of an open source utility class performing the most common imaging tasks, I'd be happy to hear about it. Thanks in advance.

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  • Nonblocking texture upload on iPhone and other OpenGL ES platforms

    - by spurserh
    Hello, I am doing some work which involves drawing video frames in real time in OpenGL ES. Right now I am using glTexImage2D to transfer the data, in the absence of Pixel Buffer Objects and the like. A below answer suggests that glTexImage2D is always blocking, even if texture object referenced does is not used for any drawing. Is there a way to do a nonblocking texture upload with OpenGL ES (any version)? Thank you very much, Sean

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  • Visual Python - Visualize graphs relating to a movement

    - by Francisco P.
    Hello, everyone! I'm working with visual python on a project where I need to simulate a physical movement. I'd like to present, in a different window than the one the actual, 3D sim is running, two graphs, both related to the movement: How the velocity and angular velocity progress over time. How the movement and rotation progress over time. All these vars are refreshed once per cycle (inside a while(true)) How can I accomplish this? Thank you for your time!

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  • Video Synthesis - Making waves, patterns, gradients...

    - by Nathan
    I'm writing a program to generate some wild visuals. So far I can paint each pixel with a random blue value: for (y = 0; y < YMAX; y++) { for (x = 0; x < XMAX; x++) { b = rand() % 255; setPixelColor(x,y,r,g,b); } } I'd like to do more than just make blue noise, but I'm not sure where to start (Google isn't helping me much today), so it would be great if you could share anything you know on the subject or some links to related resources.

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  • Detecting Asymptotes in a Graph

    - by nasufara
    I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with asymptotes. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with asymptotes using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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  • iPhone app crashes on start-up, in stack-trace only messages from built-in frameworks

    - by Aleksejs
    My app some times crashes at start-up. In stack-trace only messages from built-in frameworks. An excerpt from a crash log: OS Version: iPhone OS 3.1.3 (7E18) Report Version: 104 Exception Type: EXC_BAD_ACCESS (SIGBUS) Exception Codes: KERN_PROTECTION_FAILURE at 0x000e6000 Crashed Thread: 0 Thread 0 Crashed: 0 CoreGraphics 0x339305d8 argb32_image_mark_RGB32 + 704 1 CoreGraphics 0x338dbcd4 argb32_image + 1640 2 libRIP.A.dylib 0x320d99f0 ripl_Mark 3 libRIP.A.dylib 0x320db3ac ripl_BltImage 4 libRIP.A.dylib 0x320cc2a0 ripc_RenderImage 5 libRIP.A.dylib 0x320d5238 ripc_DrawImage 6 CoreGraphics 0x338d7da4 CGContextDelegateDrawImage + 80 7 CoreGraphics 0x338d7d14 CGContextDrawImage + 364 8 UIKit 0x324ee68c compositeCGImageRefInRect 9 UIKit 0x324ee564 -[UIImage(UIImageDeprecated) compositeToRect:fromRect:operation:fraction:] 10 UIKit 0x32556f44 -[UINavigationBar drawBackButtonBackgroundInRect:withStyle:pressed:] 11 UIKit 0x32556b00 -[UINavigationItemButtonView drawRect:] 12 UIKit 0x324ecbc4 -[UIView(CALayerDelegate) drawLayer:inContext:] 13 QuartzCore 0x311cacfc -[CALayer drawInContext:] 14 QuartzCore 0x311cab00 backing_callback 15 QuartzCore 0x311ca388 CABackingStoreUpdate 16 QuartzCore 0x311c978c -[CALayer _display] 17 QuartzCore 0x311c941c -[CALayer display] 18 QuartzCore 0x311c9368 CALayerDisplayIfNeeded 19 QuartzCore 0x311c8848 CA::Context::commit_transaction(CA::Transaction*) 20 QuartzCore 0x311c846c CA::Transaction::commit() 21 QuartzCore 0x311c8318 +[CATransaction flush] 22 UIKit 0x324f5e94 -[UIApplication _reportAppLaunchFinished] 23 UIKit 0x324a7a80 -[UIApplication _runWithURL:sourceBundleID:] 24 UIKit 0x324f8df8 -[UIApplication handleEvent:withNewEvent:] 25 UIKit 0x324f8634 -[UIApplication sendEvent:] 26 UIKit 0x324f808c _UIApplicationHandleEvent 27 GraphicsServices 0x335067dc PurpleEventCallback 28 CoreFoundation 0x323f5524 CFRunLoopRunSpecific 29 CoreFoundation 0x323f4c18 CFRunLoopRunInMode 30 UIKit 0x324a6c00 -[UIApplication _run] 31 UIKit 0x324a5228 UIApplicationMain 32 Journaler 0x000029ac main (main.m:14) 33 Journaler 0x00002948 start + 44 File main.m is simple as possible: #import <UIKit/UIKit.h> int main(int argc, char *argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; int retVal = UIApplicationMain(argc, argv, nil, nil); // line 14 [pool release]; return retVal; } What my cause the app to crash?

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  • Can a GeneralPath be modified?

    - by Dov
    java2d is fairly expressive, but requires constructing lots of objects. In contrast, the older API would let you call methods to draw various shapes, but lacks all the new features like transparency, stroke, etc. Java has fairly high costs associated with object creation. For speed, I would like to create a GeneralPath whose structure does not change, but go in and change the x,y points inside. path = new GeneralPath(GeneralPath.WIND_EVEN_ODD, 10); path.moveTo(x,y); path.lineTo(x2, y2); double len = Math.sqrt((x2-x)*(x2-x) + (y2-y)*(y2-y)); double dx = (x-x2) * headLen / len; double dy = (y-y2) * headLen / len; double dx2 = -dy * (headWidth/headLen); double dy2 = dx * (headWidth/headLen); path.lineTo(x2 + dx + dx2, y2 + dy + dy2); path.moveTo(x2 + dx - dx2, y2 + dy - dy2); path.lineTo(x2,y2); This one isn't even that long. Imagine a much longer sequence of commands, and only the ones on the end are changing. I just want to be able to overwrite commands, to have an iterator effectively. Does that exist?

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  • Drawing triangle/arrow on a line with CGContext

    - by Pete
    Hi, I am using the framework of route-me for working with locations. In this code the path between two markers(points) will be drawn as a line. My Question: "What code should I add if I want to add an arrow in the middle(or top) of the line, so that it points the direction" Thanks - (void)drawInContext:(CGContextRef)theContext { renderedScale = [contents metersPerPixel]; float scale = 1.0f / [contents metersPerPixel]; float scaledLineWidth = lineWidth; if(!scaleLineWidth) { scaledLineWidth *= renderedScale; } //NSLog(@"line width = %f, content scale = %f", scaledLineWidth, renderedScale); CGContextScaleCTM(theContext, scale, scale); CGContextBeginPath(theContext); CGContextAddPath(theContext, path); CGContextSetLineWidth(theContext, scaledLineWidth); CGContextSetStrokeColorWithColor(theContext, [lineColor CGColor]); CGContextSetFillColorWithColor(theContext, [fillColor CGColor]); // according to Apple's documentation, DrawPath closes the path if it's a filled style, so a call to ClosePath isn't necessary CGContextDrawPath(theContext, drawingMode); }

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  • Image animation over CGContextDrawPDFPage

    - by BittenApple
    I have a pdf page displayed with CGContextDrawPDFPage in QuartzDemo sample application. I want to keep this page shown and have an image slide in from top over this page, just as it can be seen in the iBooks application. It's a book, the sliding image is a bookmark that slides in when you are about to close the book. I added this code by DyingCactus (hint: im a newbie to obj c and iphone dev) as follows: In QuartzViewController.m, the animation starts to show but the view slides away before the animation is finished, in fact I think the animation goes on while the view is sliding away. -(void)viewWillDisappear:(BOOL)animated { [self.quartzView setFrame:CGRectMake(150, -200, 100, 200)]; [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:1.0]; [self.quartzView setFrame:CGRectMake(150, 0, 100, 200)]; [UIView commitAnimations]; } How can I keep the view visible and finish the animation before view disappears?

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