NSImage和PDFImageRep缓存仍然只能以一种分辨率绘制

Question

I have an NSImage, initialized with PDF data, created like this:

NSData* data = [view dataWithPDFInsideRect:view.bounds];
slideImage = [[NSImage alloc] initWithData:data];

The slideImage is now the size of the view .

When I try to render the image in an NSImageView , it only draws sharp when the image view is exactly the original size of the image, even if you clear the cache or change the image size. I tried setting the cacheMode to NSImageCacheNever , which also didn't work. The only image rep in the image is the PDF one, and when I render it to a PDF file it shows that it's vector.

As a workaround, I create a NSBitmapImageRep with a different size, call drawInRect on the original image, and put the bitmap representation inside a new NSImage and render that, which works, but it feels like it's not optimal:

- (NSBitmapImageRep*)drawToBitmapOfWidth:(NSInteger)width
                               andHeight:(NSInteger)height
                               withScale:(CGFloat)scale
{
    NSBitmapImageRep *bmpImageRep = [[NSBitmapImageRep alloc]
                                     initWithBitmapDataPlanes:NULL
                                     pixelsWide:width * scale
                                     pixelsHigh:height * scale
                                     bitsPerSample:8
                                     samplesPerPixel:4
                                     hasAlpha:YES
                                     isPlanar:NO
                                     colorSpaceName:NSCalibratedRGBColorSpace
                                     bitmapFormat:NSAlphaFirstBitmapFormat
                                     bytesPerRow:0
                                     bitsPerPixel:0
                                     ];
    bmpImageRep = [bmpImageRep bitmapImageRepByRetaggingWithColorSpace:
                   [NSColorSpace sRGBColorSpace]];
    [bmpImageRep setSize:NSMakeSize(width, height)];
    NSGraphicsContext *bitmapContext = [NSGraphicsContext graphicsContextWithBitmapImageRep:bmpImageRep];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:bitmapContext];

    [self drawInRect:NSMakeRect(0, 0, width, height) fromRect:NSZeroRect operation:NSCompositeCopy fraction:1];

    [NSGraphicsContext restoreGraphicsState];
    return bmpImageRep;
}

- (NSImage*)rasterizedImageForSize:(NSSize)size
{
    NSImage* newImage = [[NSImage alloc] initWithSize:size];
    NSBitmapImageRep* rep = [self drawToBitmapOfWidth:size.width andHeight:size.height withScale:1];
    [newImage addRepresentation:rep];
    return newImage;
}

How can I get the PDF to render nicely at any size without resorting to hacks like mine?

Answer 1

The point of NSImage is that you create it with the size (in points) that you want it to be. The backing representation can be vector based (eg PDF), and the NSImage is resolution independent (ie it supports different pixels per point), but the NSImage still has a fixed size (in points).

One one the points of an NSImage is that it will / can add a cache representation to speed up subsequent drawing.

If you need to draw a PDF to multiple sizes, and you want to use an NSImage, you're probably best of creating an NSImage for your given target size. If you want to, you can keep the NSPDFImageRef around -- I don't think it'll save you much.

Answer 2

We tried the following:

NSPDFImageRep* rep = self.representations.lastObject;
return [NSImage imageWithSize:size flipped:NO drawingHandler:^BOOL (NSRect dstRect)
{
    [[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationHigh];
    [rep drawInRect:dstRect fromRect:NSZeroRect operation:NSCompositeCopy fraction:1 respectFlipped:YES hints:@{
            NSImageHintInterpolation: @(NSImageInterpolationHigh)
    }];
    return YES;
}];

And that does give you nice results when scaling up, but makes for blurry images when scaling down.