以下代码在图像上绘制一些文本:
UIGraphicsBeginImageContext(image.size);
[image drawAtPoint:CGPointZero];
NSString *stamp = @"Internal Use Only";
[stamp drawAtPoint:CGPointMake(10, 10) withFont:[UIFont systemFontOfSize:32]];
UIImage *stampedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
如果使用不同的字符串再次执行代码,则两个字符串会合并且不清晰。我怎样才能使这个 drawAtPoint() 覆盖以前的字符串?