On Fri, May 28, 2010 at 1:36 AM, Graham Cox <graham....@bigpond.com> wrote: > I understand that contexts can (still) be flipped. > > Let's break this down a bit, since I'm fighting two problems simultaneously > here. First, PDF File generation. > > Using the code I quoted, I generate PDF data in a flipped context. The > flipped context matches the coordinate system that drawn objects expect. As > such, objects and text are all positioned in the correct relative locations. > > If I write the PDF data immediately to a file, no NSImage or rep involved, > result is an upside down PDF file when it's opened in Preview. > > If I generate the PDF data in a non-flipped context, the PDF File is still > upside down, with the added problem that text glyphs are inverted > individually. > > So at no point have I done anything with this image like draw it anywhere. > How can it even be possible for PDF data in a file to be inverted? The > problem appears to be with the PDF generation, so what's wrong there?
My understanding of this isn't the best, but here's how I see it: The idea of "flipped/not-flipped" is a Cocoa idea. But CGContexts aren't Cocoa and they don't have the notion of being flipped or not. That's exactly why the +[NSGraphicsContext graphicsContextWithGraphicsPort:flipped:] call has to ask if the CG context it is getting is flipped or not! If the CG context knew, NSGraphicsContext could just ask it. So, your view is flipped and all your drawing operations assume a flipped context. How do we get there for PDFs? Simple... we apply a Current Transformation Matrix (CTM) that flips the CG context! Something like this should work: // Move the origin to the top of the context CGContextTranslateCTM( pdfContext, 0.0, size.height ); // Now "flip" the y-axis so that it increases downwards CGContextScaleCTM( pdfContext, 1.0, -1.0 ); And now you would pass flipped:YES to +[NSGraphicsContext graphicsContextWithGraphicsPort:flipped:] because we just flipped it! Basically, you were almost there. You got a perfect PDF file, just upside down. Another way to look at all of this is "what CTM do I need to apply to get everything right side up?" The answer is, flip the y-axis over y=0 (the x-axis) and add the height. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
