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

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?

Answer 1

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 ;-)

Answer 2

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];
}