Erase drawing made on image view - ios

Question

So, I am working on a virtual wall painting app.
I am able to draw some random lines by moving my finger on the image view(which has an image in it). Now I am trying to erase the drawings made on it without success as of yet.
I googled to find some solution and this line below came as full on recommended :-
CGContextSetBlendMode(UIGraphicsGetCurrentContext(),kCGBlendModeClear);
Using this drawing can be erased,but it also erases the image on which the drawing are done. Is there any way to prevent the image from getting erased ? only erase the drawing made on it?
Following is the code I am using to erase the drawings :-
In touchesMoved:-
UITouch *touch = [touches anyObject];
CGPoint previousPoint = [touch locationInView:self.upperImageView];
UIGraphicsBeginImageContext(self.upperImageView.frame.size);
[self.upperImageView.image drawInRect:CGRectMake(0, 0, self.upperImageView.frame.size.width, self.upperImageView.frame.size.height)];
CGContextSaveGState(UIGraphicsGetCurrentContext());
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(),YES);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), eraserCap);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 45.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.25, 0.25, 0.25, 1.0);
CGMutablePathRef pathB = CGPathCreateMutable();
CGPathMoveToPoint(pathB,nil,location.x,location.y);
CGPathAddLineToPoint(pathB,nil,previousPoint.x,previousPoint.y);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
CGContextAddPath(UIGraphicsGetCurrentContext(),pathB);
CGContextStrokePath(UIGraphicsGetCurrentContext());
upperImageView.image = UIGraphicsGetImageFromCurrentImageContext();
CGContextRestoreGState(UIGraphicsGetCurrentContext());
UIGraphicsEndImageContext();
location = previousPoint;
and in touchesEnded:-
UITouch *touch = [touches anyObject];
CGPoint previousPoint = [touch locationInView:self.upperImageView];
UIGraphicsBeginImageContext(self.upperImageView.frame.size);
[self.upperImageView.image drawInRect:CGRectMake(0, 0, self.upperImageView.frame.size.width, self.upperImageView.frame.size.height)];
CGContextSaveGState(UIGraphicsGetCurrentContext());
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), YES);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), eraserCap);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0,1.0,1.0, 0.0);
CGMutablePathRef pathB = CGPathCreateMutable();
CGPathMoveToPoint(pathB, nil, location.x, location.y);
CGPathAddLineToPoint(pathB, nil, previousPoint.x, previousPoint.y);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
CGContextAddPath(UIGraphicsGetCurrentContext(),pathB);
CGContextStrokePath(UIGraphicsGetCurrentContext());
self.upperImageView.image = UIGraphicsGetImageFromCurrentImageContext();
// CGContextRestoreGState(UIGraphicsGetCurrentContext());
UIGraphicsEndImageContext();
previousPoint = location;
Is there anything I am doing wrong ? Please guide me in the right direction here, any help will be truly appreciated.

Answer 1

You can use different views for your image and drawings.
Or keep drawn paths in the array and delete each path separately.

Answer 2

Move all of your drawing to a separate UIView that overlays the UIImageView. That way, when you go to "clear" the contents, the original UIImageView is still completely intact underneath.
Something like this will get you set up:
- (void)viewWillAppear {
// Assumes you add a property of type UIView
self.drawingView = [[UIView alloc] initWithFrame:self.upperImageView.bounds];
[self.upperImageView addSubview:drawingView];
}
Then, your drawing code needs to only change to this (notice that you won't need to redraw the image any more):
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint previousPoint = [touch locationInView:self.drawingView];
UIGraphicsBeginImageContext(self.drawingView.frame.size);
CGContextSaveGState(UIGraphicsGetCurrentContext());
CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(),YES);
CGContextSetLineCap(UIGraphicsGetCurrentContext(), eraserCap);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 45.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 0.25, 0.25, 0.25, 1.0);
CGMutablePathRef pathB = CGPathCreateMutable();
CGPathMoveToPoint(pathB,nil,location.x,location.y);
CGPathAddLineToPoint(pathB,nil,previousPoint.x,previousPoint.y);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
CGContextAddPath(UIGraphicsGetCurrentContext(),pathB);
CGContextStrokePath(UIGraphicsGetCurrentContext());
upperImageView.image = UIGraphicsGetImageFromCurrentImageContext();
CGContextRestoreGState(UIGraphicsGetCurrentContext());
UIGraphicsEndImageContext();
location = previousPoint;
}
Make similar changes in the touchesEnded: method.