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POHow to implement undo in a drawing app
 

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  1. POHow to implement undo in a drawing app
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    <p>Below is the code snippet of painting. I can do undo in a vector drawing just like storing points and remove the highest one from mutable array then redrawing.However, it does not function properly in a raster drawing.</p> <p>If I use UIGraphicsGetCurrentContext() as a context reference, undo works well. But the context of CGBitmapContextCreate() does not when issue undo action.</p> <pre><code>- (id)initWithFrame:(CGRect)frame { objArray = [[NSMutableArray alloc] init]; CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); canvas = CGBitmapContextCreate(NULL, drawImage.frame.size.width, drawImage.frame.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast); CGColorSpaceRelease(colorSpace); } return self; } </code></pre> <p>&nbsp;</p> <pre><code>- (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGImageRef imgRef = CGBitmapContextCreateImage(canvas); CGRect r = self.bounds; CGContextDrawImage(context, CGRectMake(0, 0, r.size.width, r.size.height), imgRef); if(ok) { for (int i = 0; i &lt; [objArray count]; i++) { CGPoint point = [[[objArray objectAtIndex: i] objectAtIndex:0] CGPointValue]; CGContextMoveToPoint(canvas, point.x, point.y); for (int j = 0; j &lt; [[objArray objectAtIndex:i] count]; j++) { point = [[[objArray objectAtIndex: i] objectAtIndex:j] CGPointValue]; CGContextAddLineToPoint(canvas, point.x, point.y); CGContextStrokePath(**canvas**); CGContextMoveToPoint(**canvas**, point.x, point.y); } } } CGImageRelease(imgRef); } </code></pre> <p>&nbsp;</p> <pre><code>- (void)undo:(id) sender { NSLog(@"click"); if([objArray count] &gt; 0) [objArray removeLastObject]; ok = YES; [self setNeedsDisplay]; } </code></pre> <p>&nbsp;</p> <pre><code>- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { NSMutableArray *points = [NSMutableArray array]; UITouch *touch = nil; if (touchPoint) { touch = [touches member:touchPoint]; } end = [touch locationInView:self]; [points addObject:[NSValue valueWithCGPoint:start]]; [points addObject:[NSValue valueWithCGPoint:end]]; [objArray addObject:points]; CGContextMoveToPoint(**canvas**, start.x, start.y); CGContextAddLineToPoint(**canvas**, end.x, end.y); CGContextSetLineCap(**canvas**, kCGLineCapRound); CGContextSetLineWidth(**canvas**, 40.0); CGContextStrokePath(**canvas**); start = end; [self setNeedsDisplay]; } </code></pre>
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    1. PTQuestion
    1. USMatthew Frederick
    1. USyongjoon
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    1. COYou're much more likely to get assistance if we don't have to visit a mysterious link. Make the effort required as small as possible. I have a likely answer but don't want to risk following your link.
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      1. POHow to implement undo in a drawing app
      1. USMatthew Frederick
    2. CO@Matthew Sorry for that. I removed the link and put a short description. I'd appreciate if you give me any hints.
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      1. POHow to implement undo in a drawing app
      1. USyongjoon
 

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