Constructing Paths（构建路径）

points -> a shape:多个点构成一个形状

shapes -> a path:多个形状构成一个路径

绘制过程:

    创建路径 －CGMutablePathRef  CGPathCreateMutable (void);  //CGMutablePathRef path = CGPathCreateMutable();

    画线条，并将其加入路径

          设置起点 －void  CGPathMoveToPoint (CGMutablePathRef path,const CGAffineTransform *m,CGFloat x,CGFloat y); //第二个参数:NULL

          设置终点 －void  CGPathAddLineToPoint (CGMutablePathRef path,const CGAffineTransform *m,CGFloat x,CGFloat y);

    创建上下文环境 －CGContextRef  UIGraphicsGetCurrentContext (void); //CGContextRef currentContext = UIGraphicsGetCurrentContext();

       在环境中添加路径 －void  CGContextAddPath (CGContextRef context,CGPathRef path); 

    设置相关属性 - (void)setStroke  //颜色

               － void  CGContextSetLineWidth (CGContextRef c,CGFloat width); //线宽

    绘制路径 －void  CGContextDrawPath (CGContextRef c,CGPathDrawingMode mode);

    释放 －void  CGPathRelease (CGPathRef path);

    重要的3种绘制模式 －CGPathDrawingMode :kCGPathFill, kCGPathStroke, kCGPathFillStroke  ; 

- (void)drawRect:(CGRect)rect{

    

    /* Create the path */

   CGMutablePathRef path = CGPathCreateMutable();

    

   CGRect screenBounds = [[UIScreen mainScreen] bounds];

    

    /* Start:左上 */

   CGPathMoveToPoint(path, NULL, screenBounds.origin.x,screenBounds.origin.y);

    

    /* Draw a line : 从左上到右下 */

   CGPathAddLineToPoint(path,NULL,screenBounds.size.width,screenBounds.size.height);

    

    /* Start another line:右上 */

    CGPathMoveToPoint(path,NULL,screenBounds.size.width,screenBounds.origin.y);

    

    /* Draw a line :从右上到左下 */

    CGPathAddLineToPoint(path,NULL,screenBounds.origin.x,screenBounds.size.height);

    

    /* Get the context that the path has to be drawn on */

   CGContextRef currentContext = UIGraphicsGetCurrentContext();

    

    /* Add the path*/

   CGContextAddPath(currentContext,path);

    

    /* Set the blue color as the stroke color */

    [[UIColor blueColor] setStroke];

    

    /* Draw the path with stroke color */

   CGContextDrawPath(currentContext,kCGPathStroke);

    

    /* Finally release the path object */

   CGPathRelease(path);  

}