CoreGraphics rotate and image around a point in iOS - ios

Question

I have tried everything I can think of, but none of its working. In an iOS UIView drawRect, I want a function that takes an image, a point on the image, scale, and an angle, and draws the image rotated around the given point at the center of the view. So if I want to rotate around the origin (0,0) the edge of my image will appear in the center of the view.
Here's my first version of the code:
-(void)drawImage:(UIImage*)image atAngle:(float)theta atScale:(float)scale whereCenter:(JBPoint*)center inContext:(CGContextRef)context
{
UIGraphicsPushContext(context);
//Rotate
CGContextTranslateCTM (context, -center.x, -center.y);
CGContextRotateCTM (context, theta);
CGContextTranslateCTM (context, center.x, center.y);
//Scale
CGContextScaleCTM(context, scale, scale);
//Draw
GContextDrawImage(context, self.frame, image.CGImage);
UIGraphicsPopContext();
}
However, this skewed the image such that it was not an affine transformation even though I only performed affine transformations on it.
After fiddling with it for a time, I just decided to do it by hand, and calculate the locations of the four corner points and draw it then:
-(void)drawImage:(UIImage*)image atAngle:(float)theta atScale:(float)scale whereCenter:(JBPoint*)center inContext:(CGContextRef)context
{
UIGraphicsPushContext(context);
CGContextRotateCTM (context, theta);
float ux = cos(theta);
float uy = sin(theta);
float vx = sin(theta);
float vy = -cos(theta);
CGPoint p1 = CGPointMake(self.frame.size.width/2.0f-ux*scale*center.x-vx*scale*(image.size.height - center.y), self.frame.size.height/2.0f-uy*scale*center.x-vy*scale*(image.size.height - center.y));
CGPoint p2 = CGPointMake(p1.x+ux*image.size.width*scale, p1.y+uy*image.size.width*scale);
CGPoint p3 = CGPointMake(p2.x+vx*image.size.height*scale, p2.y+vy*image.size.height*scale);
CGPoint p4 = CGPointMake(p1.x+vx*image.size.height*scale, p1.y+vy*image.size.height*scale);
//Sanity check. These all should be the same since I want to center at the center of the frame
NSLog(#"Center: %f, %f", (p1.x+p3.x)/2.0f, (p1.y+p3.y)/2.0f);
NSLog(#"Center: %f, %f", (p2.x+p4.x)/2.0f, (p2.y+p4.y)/2.0f);
NSLog(#"Center: %f, %f", self.frame.size.width/2.0f, self.frame.size.height/2.0f);
float minX = MIN(MIN(p1.x, p2.x), MIN(p3.x, p4.x));
float minY = MIN(MIN(p1.y, p2.y), MIN(p3.y, p4.y));
float maxX = MAX(MAX(p1.x, p2.x), MAX(p3.x, p4.x));
float maxY = MAX(MAX(p1.y, p2.y), MAX(p3.y, p4.y));
CGContextSetAlpha(context, alpha);
CGContextScaleCTM(context, 1, -1);
CGContextDrawImage(context, CGRectMake(minX, -minY, (maxX-minX), -(maxY-minY)), image.CGImage);
UIGraphicsPopContext();
}
This works for angles of 0, but as soon as the angle becomes 90 degrees (pi/2) the image is extremely skewed, which doesn't make any sense.
This seems to be such a simple problem. Why is it so hard? Does anyone see what I'm doing wrong?