来自NSAttributedString的“逆”NSAttributedString

Question

我从一个UIImage创建了一个NSAttributedString

UIFont *font = [UIFont systemFontOfSize:12.0f];
NSDictionary *attributes = @{NSFontAttributeName:font,
                             NSForegroundColorAttributeName:[UIColor greenColor]};

NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:title attributes:attributes];

// Create the image here
UIImage *image = [self imageFromAttributedString:attributedString];


#pragma mark - Get image from attributed string

- (UIImage *)imageFromAttributedString:(NSAttributedString *)text
{
    UIGraphicsBeginImageContextWithOptions(text.size, NO, 0.0);

    // draw in context
    [text drawAtPoint:CGPointMake(0.0, 0.0)];

    // transfer image
    UIImage *image = [UIGraphicsGetImageFromCurrentImageContext() imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    UIGraphicsEndImageContext();

    return image;
}

我的问题是，用相同的文本创建一个图像的最佳方法是什么，但是“反转”，即UIColor greenColor与白色字体文本？

Answer 1

使用NSBackgroundColorAttributeName将背景设置为绿色，并将文本设置为白色。

这些文件包括：

NSString *const NSForegroundColorAttributeName;
NSString *const NSBackgroundColorAttributeName;

在ref/doc/uid/TP40011688

Answer 2

一旦您有了图像，您可以使用核心图像过滤器反转颜色，或将蓝色更改为粉红色或红色或任何您想要的:有一个名为CIColorInvert的CI过滤器，它将简单地反转颜色，但就我个人而言，我更喜欢使用colorMatrix过滤器，它为我提供了更多的控制代码来逆转如下：

注意，这个例程假设您的起始UIImage是beginImage，输出是endImage

使用ColorMatrix：

 CIFilter *filterci = [CIFilter filterWithName:@"CIColorMatrix"  //rgreen
                                keysAndValues: kCIInputImageKey, beginImage, nil];
[filterci setValue:[CIVector vectorWithX:-1 Y:0 Z:0 W:0] forKey:@"inputRVector"]; // 5
[filterci setValue:[CIVector vectorWithX:0 Y:-1 Z:0 W:0] forKey:@"inputGVector"]; // 6
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:-1 W:0] forKey:@"inputBVector"]; // 7
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:0 W:1] forKey:@"inputAVector"]; // 8
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:0 W:0] forKey:@"inputBiasVector"];     
 CIImage *boutputImagei = [filterci outputImage];

  CGImageRef cgimgi = [context createCGImage:boutputImagei fromRect:[boutputImage extent]];
UIImage *endImage = [UIImage imageWithCGImage:cgimgi];

 CGImageRelease(cgimgi);

使用CIColorInvert：

CIFilter *filterci = [CIFilter filterWithName:@"CIColorInvert"  //rgreen
                                keysAndValues: kCIInputImageKey, beginImage, nil];
    CIImage *boutputImagei = [filterci outputImage];

  CGImageRef cgimgi = [context createCGImage:boutputImagei fromRect:[boutputImage extent]];
UIImage *endImage = [UIImage imageWithCGImage:cgimgi];

 CGImageRelease(cgimgi);