Re: Scheme for efficiently archiving images.
Re: Scheme for efficiently archiving images.
- Subject: Re: Scheme for efficiently archiving images.
- From: Graham Cox <email@hidden>
- Date: Thu, 27 Nov 2008 15:19:17 +1100
On 27 Nov 2008, at 12:49 pm, Ken Ferry wrote:
I don't have time to go much into this before I go off for the
holiday, but one thing:
On Wed, Nov 26, 2008 at 5:26 PM, Graham Cox <email@hidden>
wrote:
For images from a file, I am thinking I can copy the
original file into my package and simply archive a relative path to
it.
If you create an image with -initByReferencingURL:, the URL is all it
will archive. The 'reference' here means that the app is permitted to
assume image remains accessible at the URL. If you use
initWithContentsOfURL:, the app is contractually obligated to read the
data in immediately and no longer go back to the URL.
OK, that's fine - I'm not sure it will be a problem, but I will bear
it in mind.
I'm already running into a few other problems though, basically
because NSImage is too much of a black-box.
In order to cache the original data used to create an image, I need to
grab it before the image is actually constructed. That isn't too bad,
but for example, using [NSImage initWithPasteboard:] or [NSImage
initWithContentsOfURL:], those methods covers up a lot of
functionality. For example, it will correctly rotate an image that was
saved with a rotation flag, whereas if I grab the data from the URL
myself and make the image from that, it does not. That seems a bit
strange to me, since it's surely the same, complete data.
i.e. these two bits of code give unexpectedly different results:
return [[[NSImage alloc] initWithContentsOfURL:url] autorelease];
and
NSData* data = [NSData dataWithContentsOfURL:url];
return [[[[NSImage alloc] initWithData:data] autorelease];
Why does that happen and what can I do to fix it?
If NSImage had a way to return its retained data (if I call
setDataRetained:), none of this would seem to be necessary. Why
doesn't it?
--Graham
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