On Dec 15, 2008, at 10:50 PM, David Duncan wrote:
On Dec 15, 2008, at 12:47 PM, Thomas Clement wrote:
Alright but how am I suppose to draw a part of the image without
loading the whole image from disk first?
Creating a NSBitmapImageRep requires creating a NSData with the
whole image.
I tried using CGBitmapContextCreate but I got a malloc error again
when calling CGContextDrawImage (passing a small rect to draw).
If you use the bitmap context method, then you create a context that
is the size of the image data that you want (so if you want a 20x20
section of the image, you create a 20x20 context) then draw the
whole image to it. If you use ImageIO to load the image, then it
will only load portion of the image required to draw that area. In
order to get the correct part of the image, you would need to
translate the context (via CGContextTranslateCTM for example) to
position the image correctly.
That's right, I was not doing it correctly, this is now working.
Also I noticed I can call CGImageCreateWithImageInRect to create a new
CGImage which is a smaller area of the original image and then call
CGImageGetDataProvider and CGDataProviderCopyData to get the pixel data.
Seem easier and faster too. However CGDataProviderCopyData is 10.5
minimum.
Thanks!
Thomas
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