Want to add manual erasing option in ipad painting application by Quartz

Question

I am working on a painting application using Quartz 2D for ipad. Now I want to add an eraser option so that user can manually erase portion of his drawn line with touch.I have also background image. Can anyone please help?

what do you have implemented so far? Is there an specific problem you are having, or are you just looking for general advice? — filipe, Oct 05 '10 at 13:27
possible duplicate of [How to draw a transparent stroke (or anyway clear part of an image) on the iPhone](http://stackoverflow.com/questions/629409/how-to-draw-a-transparent-stroke-or-anyway-clear-part-of-an-image-on-the-iphone) — Brad Larson, Oct 05 '10 at 14:04
See also [Issue with erase or transparent stroke using CoreGraphics framework](http://stackoverflow.com/questions/3247491/issue-with-erase-or-transparent-stroke-using-coregraphics-framework) — Brad Larson, Oct 05 '10 at 14:05
@g-azam Please don't add irrelevant tags. This question has nothing to do with Swift. Maybe you were thinking about "iOS" instead? — Eric Aya, Aug 21 '16 at 16:07

score 4 · Answer 1 · edited Oct 09 '12 at 10:05

yes this is work well in my app ;-)

firstly you add this code in touch began

UITouch *touch = [touches anyObject];
        lastPoint = [touch locationInView:imgview];
        UIGraphicsBeginImageContext(imgview.frame.size);
        [imgview.image drawInRect:CGRectMake(0, 0, imgview.frame.size.width, imgview.frame.size.height)];
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), lineWidth);
        CGContextSetStrokeColorWithColor(UIGraphicsGetCurrentContext(), [UIColor colorWithPatternImage:img].CGColor);
        CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(), [UIColor clearColor].CGColor);
        CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
        CGContextBeginPath(UIGraphicsGetCurrentContext());

here img is ur background image then on move touch you simple write the line stroke code that code is this

UITouch *touch = [touches anyObject];
        CGPoint currentPoint = [touch locationInView:imgview];
        NSLog(@"asdasdas");
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        imgview.image = UIGraphicsGetImageFromCurrentImageContext();
        lastPoint = currentPoint;

then you see the final result is produce ;-)

score 0 · Answer 2 · edited Feb 12 '13 at 06:49

if(erase)
    {
        UITouch *touch = [touches anyObject];
        CGPoint currentTouch = [touch locationInView:extraImageVw];

        CGFloat brushSize;
        if (isEraser)
        {
            brushSize=25.0;
        }
        else
        {
            brushSize=25.0;
        }
        CGColorRef strokeColor = [UIColor whiteColor].CGColor;

        UIGraphicsBeginImageContext(extraImageVw.frame.size);

        CGContextRef context = UIGraphicsGetCurrentContext();
        [extraImageVw.image drawInRect:CGRectMake(0, 0, extraImageVw.frame.size.width, extraImageVw.frame.size.height)];
        CGContextSetLineCap(context, kCGLineCapRound);
        CGContextSetLineWidth(context, brushSize);
        if (isEraser) {
            CGContextSetStrokeColorWithColor(UIGraphicsGetCurrentContext(), [UIColor colorWithPatternImage:[UIImage imageWithContentsOfFile:fullPathToFile]].CGColor);
        }
        else
        {
            CGContextSetStrokeColorWithColor(context, strokeColor);
            CGContextSetBlendMode(context, kCGBlendModeClear);
        }
        CGContextSaveGState(UIGraphicsGetCurrentContext());
        CGContextBeginPath(context);
        CGContextMoveToPoint(context, Lastpoint.x, Lastpoint.y);
        CGContextAddLineToPoint(context, currentTouch.x, currentTouch.y);
        CGContextStrokePath(context);
        extraImageVw.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        Lastpoint = [touch locationInView:extraImageVw];


    }

Want to add manual erasing option in ipad painting application by Quartz

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