iOS 基本图形的绘制 基于bitmap 位图

- (void)imageBackGroud
{
    
    UIImageView * imageView = [[UIImageView alloc] init];
    [self.view addSubview:imageView];
    
    imageView.backgroundColor  = [UIColor redColor];
    CGRect  imageFrame = CGRectMake(100, 100, 100, 100);
    imageView.frame = imageFrame;
    
    //设置圆角
    imageView.layer.cornerRadius = 50;
    imageView.layer.masksToBounds = YES;
    
    
    UIImage *oldImage = [UIImage imageNamed:@"13"];
    
    //设置需要把图片显示的区域                           最后一个参数为scale倍数
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(200, 200), NO, 0.0);
    // 选择画布的大小和位置
    [oldImage drawInRect:self.view.bounds];
    
    // 从上下文中取得***完毕的UIImage对象
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    // 结束上下文
    UIGraphicsEndImageContext();
    
    imageView.image = newImage;
}