绘制饼状图，绘制曲线，裁剪图片，添加水印

1.绘制饼状图

a.获取上下文

CGContextRef context=UIGraphicsGetCurrentContext( );

b.绘制一段圆弧

CGContextAddArc(context , x,y,M_PI*a,M_PI*b,0);

c.绘制一条直线

CGContextAddLineToPoint( context,x,y);

d.设置闭合

CGContextClosePath(context);

e.设置线条颜色和填充色

[ [ UIColor redColor] set];

[ [ UIColor redColor] setFill];

f.渲染线条和填充色

CGContextStrokePath(context);

2.绘制曲线

a.获取上下文

CGContextRef context=UIGraphicsGetCurrentContext( );

b.设置曲线的起点

CGContextMoveToPoint(context,x,y);

c.绘制曲线

CGContextAddCurveToPoint(context,点1的x坐标，点1的y坐标，点2的x坐标，点2的y坐标，曲线的终点x坐标，终点的y坐标);

d.设置颜色

[ [ UIColor redColor ] set ];

e.渲染颜色

CGContextStrokePath( context);

3.裁剪图片

a.获取背景图

UIImage *image=[ UIImage imageNamed:图片的名字];

b.开始

UIGraphicsBeginImageContext( image.size);

c.获取山下文

CGContextRef context=UIGraphicsGetCurrentContext( );

d.

CGContextAddEllipseInRect(context, CGRect (0,0,image.size.width, image.size.height ) );

e.裁剪

CGContextClip( context );

f.

[ image drawAtPoint:CGPointZero];

g.获取裁剪后的新图片

UIImage * newImage=UIGraphicsGetImageFromCurrentImageContext( );

h.设置一个UIImageView

UIImageView *imageView=[ [ UIImageView alloc] initWithFrame:CGRectMake(0,20,image.size.width,image.size.height) ];

i.设置imageView所要显示的内容

imageView. image=newImage;

j.添加到根视图上

[ self.view addSubView: imageView];

l.结束

UIGraphicsEndImageContext( );

4.添加水印

a.获得背景图

UIImage *backImage=[ UIImage imageNamed:背景图片];

b.开始

UIGraphicsBeginImageContextWithOptions(backImage.size,动画效果，缩放比例 );

c.

[ backImage drawInRect:CGRectMake(0,0,backImage.size.width,backImage.size.height)];

d.获得水印图片

UIImage * waterImage=[ UIImage imageNamed:水印图片];

e.

[ waterImage drawInRect : CGRectMake( backImage.size.width-waterImage.size.width*0.1-100,backImage.size.height-waterImage.size.height*0.1-100,waterImage.size.width*0.2,waterImage.size.height*0.2 ) blendMode:kCGBlendModeNormal alpha:0.5];

f.获取新的图片

UIImage *newImage= UIGraphicsGetImageFromCurrentImageContext( );

g.绘制UIImageView

UIImageView *imageView=[ [ UIImageView alloc] initWithFrame:CGRectMake( 0,20,self.frame.size.width,self.frame.size.height-20)] ;

imageView.image=newImage;

[ self addSubView:imageView];