Re: Thread safe?

FROM : Trygve Inda
DATE : Sun Mar 30 17:34:19 2008

>
> On 29.03.2008, at 18:54, Adam R. Maxwell wrote:

>>
>> Drawing into an NSImage is explicitly documented to be thread safe
>> in the article you linked to, and each thread has its own graphics
>> context.  The post I linked to does indicate that you might want to
>> use [image setCacheMode:NSImageCacheNever].  If your goal is just to
>> get an NSBitmapImageRep from a file, it's probably easier just to
>> use +imageRepWithContentsOfFile:.

>
> While it is documented to be thread save you might get crashes later
> when an NSBitmapImageRep created by drawing into from an secondary
> thread gets drawn itself. The crash occurs when the image tries to
> access an NULL (offscreen) window context (it probably was originally
> drawn into).
>
> Tried to debug that on 10.5.2 (and simply worked around)...


This will never be drawn to the screen, but will be saved to disk:

NSDictionary*    imageProps = [NSDictionary dictionaryWithObject:[NSNumber
numberWithFloat:0.9] forKey:NSImageCompressionFactor];

NSData*            imageData = [myImageRep
representationUsingType:NSJPEGFileType properties:imageProps];

[imageData writeToFile:path atomically:NO];

How did you work around this?

Basically I am opening a bitmap drawing an NSImage into it, then pixel-level
tweaking the bitmap, and saving it to disk as a jpg.

Trygve