On 22/02/2010, at 10:43 AM, Alexander Hartner wrote:
I would like to rotate and offset an NSImage and then draw it onto
an NSImageView. So far I figured out to use Quartz and use
CGContextRotateCTM and CGContextTranslateCTM. I got the offset
working just fine using this, but as soon as I introduce the
rotation it rotates the image relative to the origin, rather then
the centre. I figure I need to do a combination of
CGContextTranslateCTM to move the centre of the image to the origin,
then apply a CGContextRotateCTM to rotate it and then move it back,
but I can't figure out how to best do this.
Are there any other options of doing this please let me know. I had
a look online, but all the suggestions I found seem too complicated
as there must be a simple solution to this (I hope).
CGContextSaveGState(context);
CGContextRotateCTM(context, foregrounRotation);
CGContextTranslateCTM (context, foregroundXoffset,
foregroundYoffset);
CGContextDrawImage(context, imageRect, imageBackground);
CGImageRelease(imageBackground);
CGContextRestoreGState(context);
...
Thanks in advance
Alex
To rotate around the centre of an image, first translate (move) the
image origin to the centre of your frame, then rotate, then move the
image back. You've rotated first and then moved it.
CGContextTranslateCTM(ctx, distanceXtoCentre, distanceYtoCentre);
CGContextRotateCTM(ctx, rotationValue);
CGContextTranslateCTM(ctx, -distanceXtoCentre, -distanceYtoCentre);
HTH,
Ron
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