eraser tool for vector drawings ios - ios

Question

I'm implementing my draw tools like this:
CGPoint CGPointCropByRect1(CGPoint point, CGRect rect)
{
rect = CGRectInset(rect, 5., 5.);
return CGPointMake(MIN(CGRectGetMaxX(rect), MAX(CGRectGetMinX(rect), point.x)), MIN(CGRectGetMaxY(rect), MAX(CGRectGetMinY(rect), point.y)));
}
CGFloat CGPointLengthToPoint1(CGPoint first, CGPoint second)
{
return sqrtf(powf(second.x - first.x, 2.) + powf(second.y - first.y, 2.));
}
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
self.backgroundColor = [UIColor clearColor];
_paths = [[NSMutableArray alloc] init];
}
return self;
}
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
UIColor *color = [UIColor blackColor];
CGFloat width = 5.f;
if (_isErase) {
CGContextSetStrokeColorWithColor(ctx, [UIColor clearColor].CGColor);
//CGContextSetFillColorWithColor(ctx, [UIColor clearColor].CGColor);
CGContextSetBlendMode(ctx, kCGBlendModeClear);
}
else {
CGContextSetStrokeColorWithColor(ctx, [color CGColor]);
CGContextSetLineWidth(ctx, width);
CGContextSetLineJoin(ctx, kCGLineJoinRound);
CGContextSetLineCap(ctx, kCGLineCapRound);
}
for(NSArray *array in _paths)
{
size_t index = 0;
CGPoint first = [[array objectAtIndex:index++] CGPointValue];
CGContextBeginPath(ctx);
CGContextMoveToPoint(ctx, first.x, first.y);
while (index < array.count)
{
CGPoint middlePoint = [[array objectAtIndex:index++] CGPointValue];
if(index < array.count)
{
CGPoint endPoint = [[array objectAtIndex:index++] CGPointValue];
//CGContextAddQuadCurveToPoint(ctx, middlePoint.x, middlePoint.y, endPoint.x, endPoint.y);
CGContextAddLineToPoint(ctx, middlePoint.x, middlePoint.y);
CGContextAddLineToPoint(ctx, endPoint.x, endPoint.y);
}
else
CGContextAddLineToPoint(ctx, middlePoint.x, middlePoint.y);
}
CGContextStrokePath(ctx);
}
CGContextBeginPath(ctx);
BOOL first = YES;
for(NSValue *point in _currentPath)
{
if(first)
CGContextMoveToPoint(ctx, point.CGPointValue.x, point.CGPointValue.y);
else
CGContextAddLineToPoint(ctx, point.CGPointValue.x, point.CGPointValue.y);
first = NO;
}
CGContextStrokePath(ctx);
CGContextRestoreGState(ctx);
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
_currentPath = [[NSMutableArray alloc] init];
[_currentPath addObject:[NSValue valueWithCGPoint:[[touches anyObject] locationInView:self]]];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint currentTouch = [[touches anyObject] locationInView:self];
if(!CGRectContainsPoint(self.bounds, currentTouch))
{
if(!_currentPath.count)
return;
currentTouch = CGPointCropByRect1(currentTouch, self.bounds);
CGPoint lastTouch = [[_currentPath objectAtIndex:_currentPath.count - 1] CGPointValue];
[_currentPath addObject:[NSValue valueWithCGPoint:currentTouch]];
[self setNeedsDisplayInRect:CGRectInset(CGRectMake(currentTouch.x, currentTouch.y, lastTouch.x - currentTouch.x, lastTouch.y - currentTouch.y), -10., -10.)];
return;
}
if(_currentPath.count == 0)
{
_currentPath = [[NSMutableArray alloc] init];
[_currentPath addObject:[NSValue valueWithCGPoint:currentTouch]];
return;
}
CGPoint lastTouch = [[_currentPath objectAtIndex:_currentPath.count - 1] CGPointValue];
CGFloat dim = CGPointLengthToPoint1(currentTouch, lastTouch);
if(dim > 5.)
{
[_currentPath addObject:[NSValue valueWithCGPoint:currentTouch]];
[self setNeedsDisplayInRect:CGRectInset(CGRectMake(currentTouch.x, currentTouch.y, lastTouch.x - currentTouch.x, lastTouch.y - currentTouch.y), -10., -10.)];
}
}
-(void)dropPath
{
if(_currentPath.count)
[_paths addObject:[NSArray arrayWithArray:_currentPath]];
[_currentPath release];
_currentPath = nil;
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint currentTouch = [[touches anyObject] locationInView:self];
if (!_isErase) {
//CGPoint currentTouch = [[touches anyObject] locationInView:self];
[_currentPath addObject:[NSValue valueWithCGPoint:currentTouch]];
[self dropPath];
[self setNeedsDisplay];
}
else{
[_currentPath removeObject:[NSValue valueWithCGPoint:currentTouch]];
[self dropPath];
[self setNeedsDisplay];
}
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
[self touchesEnded:touches withEvent:event];
}
#end
the main idea is- I'm storing my current points in NSArray, and then add it in another array.
How can I create a eraser? I think the main idea is to redraw the lines, but how to implement it? Is there any of examples that will make it clear for me?
The option for using background color doesn't fit.
Thanks

Answer 1

You can try adding this snipper:
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextAddPath(context, self.path);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, self.lineWidth);
CGContextSetStrokeColorWithColor(context, [UIColor clear].CGColor);
CGContextSetBlendMode(context, kCGBlendModeClear);
CGContextSetAlpha(context, self.lineAlpha);
CGContextStrokePath(context);