Transforming view coordinates with CGAffineTransform - iphone

Question

I'm fooling around with Apple's ScrollViewSuite, TapToZoom app, trying to place a view on the zoomed image. Here's what I want to do: on double tap, rotate the image by pi/2, zoom it by a factor of 8, then place a subview in the scrollView on top of the transformed image.
I know the view's desired frame in the original coordinate system. So I need to transform those coordinates to the new system after the zoom...
From the ScrollViewSuite...
- (void)handleDoubleTap:(UIGestureRecognizer *)gestureRecognizer {
// double tap zooms in
float newScale = [imageScrollView zoomScale] * 8; // my custom zoom
CGRect zoomRect = [self zoomRectForScale:newScale withCenter:[gestureRecognizer locationInView:gestureRecognizer.view]];
[imageScrollView zoomToRect:zoomRect animated:YES];
[self rotateView:imageScrollView by:M_PI_2]; // then the twist
}
My rotation code...
- (void)rotateView:(UIView *)anImageView by:(CGFloat)spin {
[UIView animateWithDuration:0.5 delay: 0.0
options: UIViewAnimationOptionAllowUserInteraction
animations:^{
anImageView.transform = CGAffineTransformMakeRotation(spin);
}
completion:^(BOOL finished){}];
}
Then, after the zoom is finished, place a view at a known location in the original coordinate system. This is where I think I need some help...
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)_scale {
CGFloat coX = scrollView.contentOffset.x;
CGFloat coY = scrollView.contentOffset.y;
// try to build the forward transformation that got us here, then invert it
CGAffineTransform rotate = CGAffineTransformMakeRotation(M_PI_2);
CGAffineTransform scale = CGAffineTransformMakeScale(_scale, _scale);
// should these be negative? some confusion here.
CGAffineTransform translate = CGAffineTransformMakeTranslation(coX, coY);
// what's the right order of concatenation on these? more confusion
CGAffineTransform aft0 = CGAffineTransformConcat(rotate, scale);
CGAffineTransform aft1 = CGAffineTransformConcat(aft0, translate);
// invert it
CGAffineTransform aft = CGAffineTransformInvert(aft1);
// this is the fixed rect in original coordinate system of the image
// the image is at 0,0 320, 300 in the view, so this will only work
// when the image is at the origin... need to fix that later,too.
CGRect rect = CGRectMake(248, 40, 90, 160);
CGRect xformRect = CGRectApplyAffineTransform(rect, aft);
// build a subview with this rect
UIView *newView = [scrollView viewWithTag:888];
if (!newView) {
newView = [[UIView alloc] initWithFrame:xformRect];
newView.backgroundColor = [UIColor yellowColor];
newView.tag = 888;
[scrollView addSubview:newView];
} else {
newView.frame = xformRect;
}
// see where it landed...
NSLog(#"%f,%f %f,%f", xformRect.origin.x, xformRect.origin.y, xformRect.size.width, xformRect.size.height);
}