iOS 关乎绘制圆弧的一个细节

1.png

#import "LXBezierPathView.h"
@interface LXBezierPathView()
@property(nonatomic,strong)UILabel *lable;
@end
@implementation LXBezierPathView

-(instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        
        
        self.lable =[[UILabel alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
        self.lable.text = @"哈哈哈";
        self.lable.textAlignment = NSTextAlignmentCenter;
        self.lable.center = CGPointMake((frame.size.width )/2, (frame.size.width)/2);
        
        [self addSubview:self.lable];
    }
    return self;
}
-(void)drawRect:(CGRect)rect{
    CAShapeLayer *shapeLayer =[[CAShapeLayer alloc]init];
    
    shapeLayer.frame = CGRectMake(0, 0, rect.size.width, rect.size.width);
    shapeLayer.lineWidth = 10;
    
    shapeLayer.fillColor =[UIColor clearColor].CGColor;
    shapeLayer.strokeColor =[UIColor redColor].CGColor;
    
    
    CGPoint center =  CGPointMake((rect.size.width )/2, (rect.size.width)/2);
   
    UIBezierPath *bezierPath =[UIBezierPath bezierPathWithArcCenter:center radius:(rect.size.width )/2 startAngle:-0.5 *M_PI endAngle:0.5 *M_PI clockwise:YES];
    shapeLayer.path = bezierPath.CGPath;
    
    [self.layer insertSublayer:shapeLayer above:shapeLayer];
    
}

我们绘制圆弧的时候，会设置贝塞尔曲线的半径为view的一半， 可是真正显示出来，会发现多了一点。这一点的长度刚好是线宽的一般。

所以需要处理的是

 UIBezierPath *bezierPath =[UIBezierPath bezierPathWithArcCenter:center radius:(rect.size.width  - 线宽)/2 startAngle:-0.5 *M_PI endAngle:0.5 *M_PI clockwise:YES];