Le 5 août 08 à 19:48, Frederick Bartram a écrit :
I am having difficulty understanding the issues involved in image
drawing speed.
I have a large, ~10K x 10K image in a scrolling view. The image is
loaded as a PNG file into an NSImageView from a nib. I am getting
large differences in the image drawing speed that I do not
understand. The image at a resolution of 72dpi, at the default
settings as loaded from the nib, draws very,very slowly.
If I change the size of the image either larger or smaller, drawing
rate increases dramatically.
If I change the resolution from 72dpi to 96dpi, for example, but not
the total pixel count then the image drawing rate also improves
greatly.
Can someone provide some guidance as to what is happening?
Many thanks,
RickB
The NSImage use differents representations to store your image data,
and probably create NSCachedImageRep when the image does not have
expected caracteristics (72 dpi ) and when you resize it.
The NSCchedImageRep use an internal representation that is optimal for
drawing, that probably explain your difference.
See the Image section of Cocoa Drawing guide for details and some tips
to change the caching behavior of an image:
http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaDrawingGuide/Images/chapter_7_section_2.html
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