Display a PDF does not work correctly in iOS 15 using CoreGraphics libraries

Question

julio_adaptive_channel OP

Created Nov ’21

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I have an application coded in objective-c that are using CoreGraphics and CGPDFDocument, it's a PDF reader.

With the release of iOS 15 i'm having problems with the rendering of certain pages in certain PDF files. The problem is not present with PDFKit.

I have also downloaded the ZoomingPDFViewer example (https://developer.apple.com/library/archive/samplecode/ZoomingPDFViewer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010281) from the official apple documentation page and i see that the same thing happens.

See the problem

Screenshot 2021-11-25 at 16.07.46.png

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Answer 1

richirobot OP

Jan ’22

I can confirm that this problem occurs since iOS 15. As far as I am concerned, I think it is due to a mismapping of the color space, in particular the alpha channel, when rendering the image to the PDF drawing context.

However, I have found a small workaround for the time being. That is setting the bitmap drawing context to non-opaque.

UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);

Regarding the CATiledLayer, one can simply set the opaque flag to false.

CATiledLayer *tiledLayer = (CATiledLayer *)[self layer];
tiledLayer.opaque = NO;

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