Question

This is part of a big project, but my problem can be simplified as:
I have a simple view with an ImageView and a “Rotate” button. Whenever I press the button, the image inside the ImageView will rotate 90 degree. From much of what I’ve found on StackOverflow and other sites, this should work (please note that my image is a square image, which has width and height equal to 464):

- (UIImage *) getRotatedImageFromImage:(UIImage*)image:(int)rotate_index
{
    UIImage *rotatedImage;

    // Get image width, height of the bounding rectangle
    CGRect boundingRect = CGRectMake(0, 0, image.size.width, image.size.height);
    NSLog(@"width = %f, height = %f",boundingRect.size.width,boundingRect.size.height);
    NSLog(@"rotate index = %d",rotate_index);

    // Create a graphics context the size of the bounding rectangle
    UIGraphicsBeginImageContext(boundingRect.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextRotateCTM(context, rotate_index*M_PI/2);

    // Draw the image into the context

    [image drawInRect:boundingRect];

    // Get an image from the context
    rotatedImage = UIGraphicsGetImageFromCurrentImageContext();

    // Clean up
    UIGraphicsEndImageContext();

    NSLog(@"rotatedImage size = (%f, %f)",rotatedImage.size.width,rotatedImage.size.height);

    return rotatedImage;
}

- (IBAction) rotateImage
{
    NSLog(@"rotate image");
    rotateIndex++;
    if (rotateIndex >= 4)
        rotateIndex = 0;
    [imageView setImage: [self getRotatedImageFromImage:imageToSubmit :rotateIndex]];
}

But it doesn’t work for some reasons. What I have is: when pressing the button, the image only appears when rotateIndex gets to 0, and the image is the same as the original image (which is expected). When rotateIndex is 1, 2, 3, the imageView displays nothing, even though the size of rotatedImage printed out is correct (i.e. 464 x 464) .
Could anyone tell me what’s going wrong?
Thanks.

Answer 1

I was able to solve my problem. Here is my solution, using CGImageRef and [UIImage imageWithCGImage: scale: orientation:]

CGImageRef cgImageRef = CGBitmapContextCreateImage(context); 
UIImageOrientation imageOrientation; 
switch (rotate_index) { 
    case 0: imageOrientation = UIImageOrientationUp; break; 
    case 1: imageOrientation = UIImageOrientationLeft; break; 
    //2 more cases for rotate_index = 2 and 3 
} 
rotatedImage = [UIImage imageWithCGImage:cgImageRef scale:1.0 orientation:imageOrientation];`