Re: Determining CGContext type at runtime

Steve Christensen

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

On Jun 19, 2020, at 10:23 PM, Graham Cox <graham@...> wrote:

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.


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