目标c - 视图上的透明绘图（UIVisualEffectView）

Question

我想在视图上创建透明绘图（就像黄色视图中的红色绘图）。 我有一些观点（UIVisualEffectView - 黄色视图），我想用手指画画，看起来我们会“擦掉”它。

我创建了UIVisualEffectView的子类并尝试绘制，但它的工作效果不佳..

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches)
    {
        CGPoint location = [touch locationInView:self];
        CGFloat drawSize = 45;
        CGRect rect = CGRectMake(location.x, location.y, drawSize, drawSize);
        [self test:rect];
    }
}

-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches)
    {
        CGPoint location = [touch locationInView:self];
        CGFloat drawSize = 45;
        [self test:CGRectMake(location.x, location.y, drawSize, drawSize)];
    }
}

-(void)test:(CGRect)rect
{
    if (!self.mask)
    {
        self.mask = [[UIView alloc]initWithFrame:self.bounds];
        self.mask.clipsToBounds = YES;
        self.mask.backgroundColor = [UIColor clearColor];
    }

    if (!self.fillLayer)
    {
        self.fillLayer = [CAShapeLayer layer];
        self.fillLayer.fillRule = kCAFillRuleEvenOdd;
        self.fillLayer.fillColor = [UIColor greenColor].CGColor;
    }

    if (!self.outerbezierPath)
    {
        self.outerbezierPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:0];
        self.outerbezierPath.usesEvenOddFillRule = NO;
    }

    self.innerCirclepath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:rect.size.height * 0.5];


    [self.outerbezierPath appendPath:self.innerCirclepath];

    [self.fillLayer removeFromSuperlayer];
    self.fillLayer.path = self.outerbezierPath.CGPath;

    [self.mask.layer addSublayer:self.fillLayer];
    self.maskView = self.mask;
}