using UIImage drawInRect still renders it upside down

问题

I have read some posts on this website about using drawInRect instead of the CGContext draw methods. It still draws it upside down? I thought using drawInRect would print it right side up with the coordinate system originating at the top left?

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
[image drawInRect:CGRectMake(x, size.height-y-height, width, height)];
UIGraphicsPopContext();
}

Notice I'm doing size.height-y-height and if I don't do that it doesn't go where I expect (assuming drawInRect using a topleft coordinate system). It renders in the correct spot with the above code but still upside down. HELP!!!!!!

UPDATE

Thanks to the answer below this is the working method

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
CGContextSaveGState(context); 
CGContextTranslateCTM(context, 0, size.height);
CGContextScaleCTM(context, 1.0, -1.0);
[image drawInRect:CGRectMake(x, y, width, height)];
CGContextRestoreGState(context);
UIGraphicsPopContext();
}

回答1:

    UIGraphicsBeginImageContext(imageViewSize);
CGContextRef imageContext = UIGraphicsGetCurrentContext();

// Draw the image in the upper left corner (0,0) with its actual size
CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

//  As it draws the image from lower right corner, 
//  following code will flip it up side down vertically.


CGContextTranslateCTM(imageContext, 0.0, 0.0);
CGContextScaleCTM(imageContext, 1.0, -1.0);

CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

来源：https://stackoverflow.com/questions/4496191/using-uiimage-drawinrect-still-renders-it-upside-down

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iphone

uiimage

cgcontext