iOS Quartz2D - 给图片加水印

UIImage *bgImage = [UIImage imageNamed:@"scene"];

// 上小文 : 基于位图(bitmap) ,  所有的东西需要绘制到一张新的图片上去

// 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)
// size : 新图片的尺寸
// opaque : YES : 不透明,  NO : 透明
// 这行代码过后.就相当于常见一张新的bitmap,也就是新的UIImage对象
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();

// 6.显示到UIImageView
self.iconView.image = newImage;

// 7.将image对象压缩为PNG格式的二进制数据
NSData *data = UIImagePNGRepresentation(newImage);
//    UIImageJPEGRepresentation(<#UIImage *image#>, <#CGFloat compressionQuality#>)

// 8.写入文件
NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"new.png"];
[data writeToFile:path atomically:YES];