UIBezierPath 的橡皮擦

我正在使用 UIBezierPath 在 iPad 应用程序中进行免费手绘。我想用橡皮擦乌贝济耶路径 /questions/tagged/uibezierpath.

不过，我想only擦除其路径中的图形。我cannot使用路径颜色作为背景颜色，因为背景上还有其他元素。

以下是我创作手绘图的方法：

- (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 = @{@"Path": myPath, @"Colors": brushPattern};
    [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];
}

存储一个用于擦除的 BOOL 值：BOOL _erase;

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

绘图时：

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