如何在iOS屏幕上画出一条线来？这是一切复杂画线的基础。
首先介绍如何运用CGPath来标定区域：

iOS有时候需要判断是否touch到某个图的区域中。这里做了个小示例，通过CGPath创建一个区域，区域是由路径做两点间线段并闭合成的区域，比如这里创建了一个简单的矩形。然后就可以用CGPath相关函数判断点是否在区域里了。

- (void)viewDidLoad {
    [super viewDidLoad];
 
    CGMutablePathRef pathRef=CGPathCreateMutable();
    CGPathMoveToPoint(pathRef, NULL, 4, 4);
    CGPathAddLineToPoint(pathRef, NULL, 4, 8);
    CGPathAddLineToPoint(pathRef, NULL, 10, 4);
    CGPathAddLineToPoint(pathRef, NULL, 4, 4);
    CGPathCloseSubpath(pathRef);
 
    CGPoint point=CGPointMake(5,7);
    CGPoint outPoint=CGPointMake(5,10);
 
    if (CGPathContainsPoint(pathRef, NULL, point, NO)) {
        NSLog(@"point in path!");
    }
 
    if (!CGPathContainsPoint(pathRef, NULL, outPoint, NO)) {
        NSLog(@"outPoint out path!");
    }

下面介绍如何画线：

首先要有个UIImageView，在本例中声明为成员变量：

@interface PathDemoViewController : UIViewController {
    UIImageView *imageView;
}

画线的代码：

- (void)viewDidLoad {
    [super viewDidLoad];
 
    imageView=[[UIImageView alloc] initWithFrame:self.view.frame];
    [self.view addSubview:imageView];
 
    self.view.backgroundColor=[UIColor blueColor];
 
    UIGraphicsBeginImageContext(imageView.frame.size);
    [imageView.image drawInRect:CGRectMake(0, 0, imageView.frame.size.width, imageView.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 15.0);
    CGContextSetAllowsAntialiasing(UIGraphicsGetCurrentContext(), YES);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), 100, 100);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), 200, 100);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    imageView.image=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}

其中：

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);

设置了线的边缘样式：

原文链接：http://marshal.easymorse.com/archives/4046