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Determining CGContext type at runtime
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Graham Cox
I need to determine whether I am drawing into a CGPDFContext or a different context at runtime.
In AppKit, I can use [NSGraphicsContext currentContextDrawingToScreen], but this is code that is passed a CGContextRef only, so that higher-level API isn’t appropriate. CGPDFContext doesn’t appear to have an associated CGPDFContextGetTypeID() function to compare with the result of CFGetTypeID(), so it’s unclear how I can do this. The reason I need to so this is that objects I am drawing can have different states according to whether they are selected in the UI or not, but when capturing the drawing into a PDF, the selection state needs to be ignored, so the drawing code needs to be able to detect what context type is so that it can do this. —Graham |
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Steve Christensen <punster@...>
I played around with it and found that bitmap (easy to create) and PDF contexts have the same CFTypeID so no help there, and that there doesn’t appear to be a public context [sub-]type property. One thing I noticed in run logging was that the context type is available in the description string, so if you’d like a fragile solution then you might do something like this. I’m not advocating for it, but if in a weak moment desperation overwhelms you... NSString* pdfDescription = [[NSString alloc] initWithFormat:@"%@", pdfContext]; NSString* bitmapDescription = [[NSString alloc] initWithFormat:@"%@", bitmapContext]; NSLog(@"pdf = %@, isPDF = %@", pdfDescription, [pdfDescription containsString:@"PDF"] ? @"YES" : @"NO"); NSLog(@"bitmap = %@, isPDF = %@", bitmapDescription, [bitmapDescription containsString:@"PDF"] ? @"YES" : @"NO"); pdf = <CGContext 0x600001ae0840> (kCGContextTypePDF), isPDF = YES bitmap = <CGContext 0x600001ae0b40> (kCGContextTypeBitmap) <<CGColorSpace 0x600000be0c60> (kCGColorSpaceDeviceRGB)> width = 100, height = 100, bpc = 8, bpp = 32, row bytes = 416 kCGImageAlphaPremultipliedFirst | 0 (default byte order) | kCGImagePixelFormatPacked (default) , isPDF = NO
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Graham Cox
Thanks — it is a bit kludgey, but might do in a pinch, as you say.
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In some cases I can set a flag on my drawing to tell it that the context should be a PDF at that time, since I am responsible for setting up that context in the first place — but at other times (such as printing), I may not get the chance. But I will explore the issue further and see if anything else comes to mind. cheers, Graham
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