How to- NSAttributedString to CGImageRef

Question

Hello!

I'm writing a QuickLook plugin. Well, everything works. Just want to try it make better ;). Thus the question.
Here is a function that returns thumbnail image and that I'm using now.

QLThumbnailRequestSetImageWithData(
QLThumbnailRequestRef thumbnail,
CFDataRef data,
CFDictionaryRef properties);
);

http://developer.apple.com/mac/library/documentation/UserExperience/Reference/QLThumbnailRequest_Ref/Reference/reference.html#//apple_ref/c/func/QLThumbnailRequestSetImageWithData

Right now I'm creating a TIFF -> encapsulated it into NSData. An example

// Setting CFDataRef
CGSize thumbnailMaxSize = QLThumbnailRequestGetMaximumSize(thumbnail);
NSMutableAttributedString *attributedString = [[[NSMutableAttributedString alloc] 
                                                   initWithString:@"dummy" 
                                                   attributes:[NSDictionary dictionaryWithObjectsAndKeys:
                                                               [NSFont fontWithName:@"Monaco" size:10], NSFontAttributeName, 
                                                               [NSColor colorWithCalibratedRed:0.0 green:0.0 blue:0.0 alpha:1.0], NSForegroundColorAttributeName, 
                                                               nil]
                                                   ] autorelease];
NSImage *thumbnailImage = [[[NSImage alloc] initWithSize:NSMakeSize(thumbnailMaxSize.width, thumbnailMaxSize.height)] autorelease];
[thumbnailImage lockFocus];
[[NSColor whiteColor] set];
NSRectFill(NSMakeRect(0, 0, thumbnailMaxSize.width, thumbnailMaxSize.height));
[attributedString drawInRect:NSMakeRect(0, 0, thumbnailMaxSize.width, thumbnailMaxSize.height)];
[thumbnailImage unlockFocus];
(CFDataRef)[thumbnailImage TIFFRepresentation]; // This is data

// Setting CFDictionaryRef
(CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:@"kUTTypeTIFF", (NSString *)kCGImageSourceTypeIdentifierHint, nil ]; // this is properties

However QuickLook provides another function to return thumbnail image, namely

QLThumbnailRequestSetImage(
QLThumbnailRequestRef thumbnail,
CGImageRef image,
CFDictionaryRef properties);

);

http://developer.apple.com/mac/library/documentation/UserExperience/Reference/QLThumbnailRequest_Ref/Reference/reference.html#//apple_ref/c/func/QLThumbnailRequestSetImage

I have a feeling that passing CGImage to the QL instead of TIFF data would help in speeding things up. However- I have never worked with CG context before. I know, the documentation is there :), but anyways- could anyone give an example how to turn that NSAttributed string into CGImageRef. An example is worth 10 times reading the documentation ;)
Any help appreciated. Thanks in advance!

Answer 1

could anyone give an example how to turn that NSAttributed string into CGImageRef.

You can't turn a string into an image; they're two completely different kinds of data, and one is two dimensional (characters over time) while the other is at-least-three dimensional (color over x and y).

What you need to do is draw the string and produce an image of the drawing. That's what you're doing now with NSImage: Creating an image and drawing the string into it.

You're asking about creating a CGImage. Creating a bitmap context, using Core Text to draw the string into it, and creating an image of the contents of the bitmap context is one way to do that.

However, you're already much closer to another solution, assuming you can require Snow Leopard. Instead of asking the NSImage for a TIFF representation, ask it for a CGImage.