UIBezierPath的橡皮擦

Question

我正在使用UIBezierPath在iPad应用程序中进行免费手绘.我想为这个UIBezierPath应用橡皮擦.但我想只通过这条路径擦除绘图.我不能使用路径颜色作为背景颜色,因为我在背景上有其他元素.有谁能够帮我.以下是我的免费手绘图代码.

     - (id)initWithFrame:(CGRect)frame
{

self = [super initWithFrame:frame];

if (self) {

    self.backgroundColor = [UIColor clearColor];

    self.opaque = NO;

    lineWidths = 10;

    brushPattern = [UIColor greenColor]; 

    pathArray = [[NSMutableArray alloc]init];

    bufferArray = [[NSMutableArray alloc]init];

    self.multipleTouchEnabled = NO;

}

return self;
}

- (void)drawRect:(CGRect)rect

 {

for (NSMutableDictionary *dictionary in pathArray) {

    UIBezierPath *_path = [dictionary objectForKey:@"Path"];

    UIColor *_colors = [dictionary objectForKey:@"Colors"];

    [_colors setStroke];

    _path.lineCapStyle = kCGLineCapRound;

    [_path stroke];


   }  

}

  -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
   {

myPath=[[UIBezierPath alloc]init];

myPath.lineWidth=lineWidths;

CGPoint touchPoint = [[touches anyObject] locationInView:self];

UITouch *mytouch=[[touches allObjects] objectAtIndex:0];

[myPath moveToPoint:[mytouch locationInView:self]];

[myPath addLineToPoint:CGPointMake(touchPoint.x, touchPoint.y)];

dict = [[NSMutableDictionary alloc] initWithObjectsAndKeys:myPath, @"Path", brushPattern, @"Colors", nil];

[pathArray addObject:dict];

[self setNeedsDisplay];

[undoManager registerUndoWithTarget:self selector:@selector(undoButtonClicked) object:nil];

  }

  -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event

 {

   UITouch *mytouch=[[touches allObjects] objectAtIndex:0];

   [myPath addLineToPoint:[mytouch locationInView:self]];

   [self setNeedsDisplay];

  }

Answer 1

存储BOOL值以进行擦除: BOOL _erase;

BOOL eraseButtonIsTapped = ...
if eraseButtonIsTapped {
    _erase = yes;
} else{
    _erase = NO;
}

绘图时:

[myPath strokeWithBlendMode:_erase?kCGBlendModeClear:kCGBlendModeNormal alpha:1.0f];