这仅仅是路径，需要添加到画布上才能显示
这里 全部没有使用 CGAffineTransform，2D 变化（仿射变化）另外再说。

不可变路径创建 CGPathRef

    CGPathRef pathRef = CGPathCreateWithRect(rect, nil);
    CGPathCreateWithEllipseInRect(rect, nil);
    CGPathCreateWithRoundedRect(rect, 10, 20, nil);

    CGPathCreateCopy(pathRef);
    CGPathCreateCopyByTransformingPath(pathRef, nil);
    CGPathCreateCopyByStrokingPath(pathRef, nil, 2, kCGLineCapButt, kCGLineJoinMiter, 4);
    /*
    typedef CF_ENUM(int32_t, CGLineJoin) {
        kCGLineJoinMiter,
        kCGLineJoinRound,
        kCGLineJoinBevel
    };
    
    typedef CF_ENUM(int32_t, CGLineCap) {
        kCGLineCapButt,
        kCGLineCapRound,
        kCGLineCapSquare
    };
    */

可变路径创建 CGMutablePathRef ，下面连点绘制

    CGMutablePathRef pathRef = CGPathCreateMutable();
    CGPathCreateMutableCopy(pathRef);
    CGPathCreateMutableCopyByTransformingPath(pathRef, nil);
    

路径绘制

基本与UIBezierPath 方法一致，就是多了两条线的圆角。

// 可变路径 用于添加下一个点
    CGMutablePathRef pathRef = CGPathCreateMutable();

起点
    CGPathMoveToPoint(pathRef, nil, 10, 20);

直线
    CGPathAddLineToPoint(pathRef, nil, 100, 200);

一次贝塞尔 控制点 终点
    CGPathAddQuadCurveToPoint(pathRef, nil, 50, 50, 100, 200);

二次贝塞尔曲线 控制点1 控制点2 终点
    CGPathAddCurveToPoint(pathRef, nil, 30, 30, 10, 200, 200, 300);

闭合当前点 和 起点
    CGPathCloseSubpath(pathRef);



矩形
    CGPathAddRect(pathRef, nil, CGRectMake(100, 100, 100, 100));

// 圆角矩形 rect ， 圆角 宽 高
    CGPathAddRoundedRect(pathRef, nil, CGRectMake(100, 100, 100, 100), 10, 40);

内切椭圆
    CGPathAddEllipseInRect(pathRef, nil, CGRectMake(100, 100, 100, 100));
    
    
弧线 （x,y）圆心 ，半径，起点  圆心角
    CGPathAddRelativeArc(pathRef, nil, 200, 200, 50, 0, M_PI/2);

同上 并增加 顺逆时针（上面的是画短的那条）（这个可以画出长的那条）
    CGPathAddArc(pathRef, nil, 200, 200, 50, 0, M_PI/2,YES);

-------------------------注意这个 UIBezierPath不好画，其他都是差不多的 ----------------------------
圆角 ：起点-（x1,y1）的直线  与 （x1,y1）-（x2,y2） 内切的圆弧 
    CGPathAddArcToPoint(pathRef, nil, 100, 100, 200, 200, 10);
-------------------------注意这个 UIBezierPath不好画，其他都是差不多的 ----------------------------


合并 路径
    CGPathAddPath(pathRef, nil, pathRef2);

路径信息

    // 返回 BOOl
    CGPathIsEmpty(pathRef);
    CGPathEqualToPath(pathRef1, pathRef2);
    CGPathIsRect(pathRef, &rect);
    CGPathContainsPoint(pathRef, nil, CGPointMake(100, 100), YES);// 最后的 YES 与 填充规则有关
    
    // 返回 对应的 结构体
    CGPathGetCurrentPoint(pathRef);
    CGPathGetBoundingBox(pathRef);// 包括内赛尔曲线的 控制点
    CGPathGetPathBoundingBox(pathRef);// 不包括 控制点

注意 Release

    CGPathRetain(pathRef);
    CGPathRelease(pathRef);// 释放

非本节内容，但是为了整体性测试，添加到画布看看效果。

    CAShapeLayer *newlayer = [[CAShapeLayer alloc] init];
    newlayer.path = pathRef;// 把上面绘制的 pathRef 赋值给画布！
    CFRelease(pathRef);// 这里 release了。
    newlayer.fillColor = [UIColor whiteColor].CGColor;
    newlayer.strokeColor = [UIColor redColor].CGColor;
    newlayer.lineWidth = 1.;
    [self.layer insertSublayer:newlayer atIndex:0];

其他

/* Return the CFTypeID for CGPathRefs. */
CG_EXTERN CFTypeID CGPathGetTypeID(void)
    CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);

 
/* Create a dashed path from `path'. The parameters `phase', `lengths', and
   `count' have the same meaning as the corresponding parameters for
   `CGContextSetLineDash'. If `transform' is non-NULL, then the elements of
   the constructed path will be transformed by `transform' before they are
   added to the path. */
CG_EXTERN CGPathRef __nullable CGPathCreateCopyByDashingPath(
    CGPathRef __nullable path, const CGAffineTransform * __nullable transform,
    CGFloat phase, const CGFloat * __nullable lengths, size_t count)
    CG_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_5_0);

 
/* Add each rectangle specified by `rects', an array of `count' CGRects, to
   `path'. If `m' is non-NULL, then first transform each rectangle by `m'
   before adding it to `path'. */
CG_EXTERN void CGPathAddRects(CGMutablePathRef __nullable path,
    const CGAffineTransform * __nullable m, const CGRect * __nullable rects,
    size_t count)
    CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);

/* Move to the first element of `points', an array of `count' CGPoints, and
   append a line from each point to the next point in `points'. If `m' is
   non-NULL, then first transform each point by `m'. */
CG_EXTERN void CGPathAddLines(CGMutablePathRef __nullable path,
    const CGAffineTransform * __nullable m, const CGPoint * __nullable points,
    size_t count)
    CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);

 

/* The types of path elements returned by `CGPathApply'. */
typedef CF_ENUM(int32_t, CGPathElementType) {
  kCGPathElementMoveToPoint,
  kCGPathElementAddLineToPoint,
  kCGPathElementAddQuadCurveToPoint,
  kCGPathElementAddCurveToPoint,
  kCGPathElementCloseSubpath
};

/* An element of a path returned by `CGPathApply'. */
struct CGPathElement {
  CGPathElementType type;
  CGPoint *  points;
};
typedef struct CGPathElement CGPathElement;

/* The prototype for the function called by `CGPathApplyFunction'. */
typedef void (*CGPathApplierFunction)(void * __nullable info,
  const CGPathElement *  element);

/* For element of `path', call `function', passing it the path element and
   `info'. */
CG_EXTERN void CGPathApply(CGPathRef __nullable path, void * __nullable info,
    CGPathApplierFunction __nullable function)
    CG_AVAILABLE_STARTING(__MAC_10_2, __IPHONE_2_0);