调整 PDF NSImage OSX

Question

我正在更新一个调整图像大小的应用程序 Mac。我想要做的是，如果用户导入要调整大小且具有 PDFImageRep 的图像，则使用我选择的分辨率保存一个新的 PDF 文件。

到目前为止，我已尝试以新尺寸绘制图像，如：

- (NSImage*)imageAtSize:(NSSize)newSize
{
    NSImage *resizedImage = [[NSImage alloc] initWithSize:newSize];

    [resizedImage lockFocus];
    [self drawInRect:NSMakeRect(0, 0, newSize.width, newSize.height)
            fromRect:NSMakeRect(0, 0, self.size.width, self.size.height)
           operation:NSCompositeSourceOver fraction:1.0];
    [resizedImage unlockFocus];

    return resizedImage;
}

但这会丢失 PDF 图像表示，因此导致我的保存代码失败。

- (void)saveAsPDFWithOutputDirectory:(NSURL *)outputDirectory size:(NSSize)newSize
{
    NSPDFImageRep *pdfRep = [self PDFImageRep];
    [pdfRep setSize:newSize];

    NSError *error = nil;
    [pdfRep.PDFRepresentation writeToURL:outputDirectory options:NSDataWritingAtomic error:&error];
    if (error)
    {
        CLS_LOG(@"Error saving image: %@", error);
    }
}

那我该怎么做呢。我将要使用的图像应该是基于矢量的，所以有什么方法可以更新 PDF 上的属性以指定新的分辨率？

Answer 1

试试下面的方法。这会创建一个新的 PDF 数据对象，您可以将其保存到文件中。

// pdfData is a CFMutableDataRef
// auxInfo is a CFDictionary
// bounds is your new size in points!
CGDataConsumerRef consumer = CGDataConsumerCreateWithCFData(pdfData);
CGContextRef context = CGPDFContextCreate(consumer, &bounds, auxInfo);
CGPDFContextBeginPage(context, NULL);
NSGraphicsContext *gc = [NSGraphicsContext graphicsContextWithGraphicsPort:context flipped:NO];
[NSGraphicsContext saveGraphicsState];
[NSGraphicsContext setCurrentContext:gc];

// Your drawing code here
// You probably want to draw your NSImage here in the bounds

[NSGraphicsContext restoreGraphicsState];
CGPDFContextEndPage(context);
CGPDFContextClose(context);
CGContextRelease(context);
CGDataConsumerRelease(consumer);

然后将pdfData保存到文件

Answer 2

感谢 Jacob 提供正确答案。如果有人感兴趣，我用 Jacob 的技术写的完整类别是：

@implementation NSImage (MKBSaveAsPDF)

- (BOOL)isPDF
{
    return ([self PDFImageRep] != nil);
}

- (NSPDFImageRep  * _Nullable)PDFImageRep
{
    for (NSImageRep *imageRep in self.representations)
    {
        if ([imageRep isKindOfClass:[NSPDFImageRep class]]){
            return (NSPDFImageRep*)imageRep;
        }
    }

    return nil;
}

- (void)saveAsPDFWithOutputDirectory:(NSURL *)outputDirectory size:(NSSize)newSize
{
    NSPDFImageRep *pdfRep = self.PDFImageRep;

    NSMutableData *mutablePDFRef = [[NSMutableData alloc]initWithData:pdfRep.PDFRepresentation];

    CFMutableDataRef pdfDataRef = (__bridge CFMutableDataRef)(mutablePDFRef);
    CGRect bounds = CGRectMake(0, 0, newSize.width, newSize.height);

    CGDataConsumerRef consumer = CGDataConsumerCreateWithCFData(pdfDataRef);
    CGContextRef context = CGPDFContextCreate(consumer, &bounds, nil);
    CGPDFContextBeginPage(context, NULL);
    NSGraphicsContext *gc = [NSGraphicsContext graphicsContextWithGraphicsPort:context flipped:NO];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:gc];

    [self drawInRect:NSMakeRect(0, 0, newSize.width, newSize.height)];

    [NSGraphicsContext restoreGraphicsState];
    CGPDFContextEndPage(context);
    CGPDFContextClose(context);
    CGContextRelease(context);
    CGDataConsumerRelease(consumer);


    NSError *error = nil;

    NSData *pdfData = (__bridge NSData *)(pdfDataRef);
    [pdfData writeToURL:outputDirectory options:NSDataWritingAtomic error:&error];
    if (error)
    {
        NSLog(@"Error saving image: %@", error);
    }
}

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