iPhone: How does CGContextConcatCTM affect CGContextDrawImage speed?
<p>I am seeing dramatic differences in drawing speed depending on whether I transform my context.</p>

<pre><code>- (void)drawLayer:(CALayer *)myLayer inContext:(CGContextRef)context {
 NSDate *startDate = [[NSDate date] retain];

 //CGContextConcatCTM(context, finalTransform);
    CGContextDrawImage(context, imageRect, imageRef);

 NSLog(@"%f", [[NSDate date] timeIntervalSinceDate:startDate]);
}
</code></pre>

<p>Average output:<br>
- With transform = 0.0125<br>
- Without transform = 0.000175</p>

<p>The image is about 100x100 and I am transforming it be to slightly less than iPad screen resolution.  The pixel data of this image often needs to be updated which is why performance is an issue. </p>

<p>Is this dramatic difference in drawing time (more than 50 times faster) to be expected?  Is there a better way to apply a scaling transform when drawing to the screen?</p>
