内容包括 图片水印，图片裁剪，屏幕截图，背景平铺

1、图片水印功能

#import "UIImage+MJ.h"

@implementation UIImage (MJ)
+ (instancetype)waterImageWithBg:(NSString *)bg logo:(NSString *)logo
{
    UIImage *bgImage = [UIImage imageNamed:bg];
    
    // 1.创建一个基于位图的上下文(开启一个基于位图的上下文)
    UIGraphicsBeginImageContextWithOptions(bgImage.size, NO, 0.0);
    
    // 2.画背景
    [bgImage drawInRect:CGRectMake(0, 0, bgImage.size.width, bgImage.size.height)];
    
    // 3.画右下角的水印
    UIImage *waterImage = [UIImage imageNamed:logo];
    CGFloat scale = 0.2;
    CGFloat margin = 5;
    CGFloat waterW = waterImage.size.width * scale;
    CGFloat waterH = waterImage.size.height * scale;
    CGFloat waterX = bgImage.size.width - waterW - margin;
    CGFloat waterY = bgImage.size.height - waterH - margin;
    [waterImage drawInRect:CGRectMake(waterX, waterY, waterW, waterH)];
    
    // 4.从上下文中取得制作完毕的UIImage对象
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 5.结束上下文
    UIGraphicsEndImageContext();
    
    return newImage;
}
@end

 
    // 1.返回水印图片
    UIImage *newImage = [UIImage waterImageWithBg:@"scene" logo:@"logo"];
    
    // 2.显示图片
    self.iconView.image = newImage;

#import "UIImage+MJ.h"

@implementation UIImage (MJ)
+ (instancetype)circleImageWithName:(NSString *)name borderWidth:(CGFloat)borderWidth borderColor:(UIColor *)borderColor
{
    // 1.加载原图
    UIImage *oldImage = [UIImage imageNamed:name];
    
    // 2.开启上下文
    CGFloat imageW = oldImage.size.width + 2 * borderWidth;
    CGFloat imageH = oldImage.size.height + 2 * borderWidth;
    CGSize imageSize = CGSizeMake(imageW, imageH);
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);
    
    // 3.取得当前的上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    
    // 4.画边框(大圆)
    [borderColor set];
    CGFloat bigRadius = imageW * 0.5; // 大圆半径
    CGFloat centerX = bigRadius; // 圆心
    CGFloat centerY = bigRadius;
    CGContextAddArc(ctx, centerX, centerY, bigRadius, 0, M_PI * 2, 0);
    CGContextFillPath(ctx); // 画圆
    
    // 5.小圆
    CGFloat smallRadius = bigRadius - borderWidth;
    CGContextAddArc(ctx, centerX, centerY, smallRadius, 0, M_PI * 2, 0);
    // 裁剪(后面画的东西才会受裁剪的影响)
    CGContextClip(ctx);
    
    // 6.画图
    [oldImage drawInRect:CGRectMake(borderWidth, borderWidth, oldImage.size.width, oldImage.size.height)];
    
    // 7.取图
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 8.结束上下文
    UIGraphicsEndImageContext();
    
    return newImage;
}
@end

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    UIImage *newImage = [UIImage circleImageWithName:@"me" borderWidth:3 borderColor:[UIColor whiteColor]];
    self.iconView.image = newImage;
    
    NSData *data = http://www.mamicode.com/UIImagePNGRepresentation(newImage);>
3、屏幕截图
#import "UIImage+MJ.h"

@implementation UIImage (MJ)
+ (instancetype)captureWithView:(UIView *)view
{
    // 1.开启上下文
    UIGraphicsBeginImageContextWithOptions(view.frame.size, NO, 0.0);
    
    // 2.将控制器view的layer渲染到上下文
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    
    // 3.取出图片
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 4.结束上下文
    UIGraphicsEndImageContext();
    
    return newImage;
}
@end

调用
- (IBAction)clip {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        // 1.捕捉
        UIImage *newImage = [UIImage captureWithView:self.view];
        
        // 2.写文件
        NSData *data = http://www.mamicode.com/UIImagePNGRepresentation(newImage);>
4，背景拉伸
- (void)imageBg
{
    UIImage *oldImage = [UIImage imageNamed:@"me"];
    
    UIGraphicsBeginImageContextWithOptions(self.view.frame.size, NO, 0.0);
    [oldImage drawInRect:self.view.bounds];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    self.view.backgroundColor = [UIColor colorWithPatternImage:newImage];
}

5、背景平铺
- (void)viewDidLoad
{
    [super viewDidLoad];
    
//    self.view.backgroundColor = [UIColor redColor];
    
    // 1.创建一行背景图片
    CGFloat rowW = self.view.frame.size.width;
//    CGFloat rowH = 40;
    CGFloat rowH = 30;
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(rowW, rowH), NO, 0.0);
    
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    // 画矩形框
    [[UIColor redColor] set];
    CGContextAddRect(ctx, CGRectMake(0, 0, rowW, rowH));
    CGContextFillPath(ctx);
    
    // 2.画线
    [[UIColor greenColor] set];
    CGFloat lineWidth = 2;
    CGContextSetLineWidth(ctx, lineWidth);
    CGFloat dividerX = 0;
    CGFloat dividerY = rowH - lineWidth;
    CGContextMoveToPoint(ctx, dividerX, dividerY);
    CGContextAddLineToPoint(ctx, rowW - dividerX, dividerY);
    CGContextStrokePath(ctx);
    
    // 3.取图
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // 4.结束上下文
    UIGraphicsEndImageContext();
    
    // 5.设置为背景
    self.textView.backgroundColor = [UIColor colorWithPatternImage:newImage];
}