IDTMessaging Test

ViewController.m

// 7. Briefly discuss pixelmap image rotation algorithms and their execution times (O(*)). If you would write an image rotation algorithm, do you find anything useful in the iOS Accelerate framework?

- (UIImage *)rotateImage:(UIImage *)sourceImage withDegrees:(CGFloat)degrees {
    vImage_Buffer sourceBuffer = [self bufferFromImage:sourceImage];
    vImage_Buffer destinationBuffer = [self newBufferForBuffer:sourceBuffer];
    
    CGFloat radians = [self radiansFromDegrees:degrees];
    
    Pixel_8 backColor = 0;
    vImageRotate_Planar8(&sourceBuffer, &destinationBuffer, NULL, radians, backColor, 0);
    
    return [self imageFromvBuffer:destinationBuffer];
}

- (UIImage *)imageFromvBuffer:(vImage_Buffer)buffer {
    CGColorSpaceRef grayColorSpace = CGColorSpaceCreateDeviceGray();
    
    CGContextRef context = CGBitmapContextCreate(buffer.data,
                                                 buffer.width,
                                                 buffer.height,
                                                 8,
                                                 buffer.width,
                                                 grayColorSpace,
                                                 0);
    
    CGImageRef dstImage = CGBitmapContextCreateImage(context);
    
    CGColorSpaceRelease(grayColorSpace);
    CGContextRelease(context);
    
    return [[UIImage alloc] initWithCGImage:dstImage];
}

- (vImage_Buffer)bufferFromImage:(UIImage *)image {
    CGImageRef imageRef = [image CGImage];
    size_t width  = CGImageGetWidth(imageRef);
    size_t height = CGImageGetHeight(imageRef);
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    Pixel_8 *bitmap = (Pixel_8 *)malloc(width * height * sizeof(Pixel_8));
    
    long bytesPerPixel = 1;
    long bytesPerRow = bytesPerPixel * width;
    long bitsPerComponent = 8;
    
    CGContextRef context = CGBitmapContextCreate(bitmap,
                                                 width,
                                                 height,
                                                 bitsPerComponent,
                                                 bytesPerRow,
                                                 colorSpace,
                                                 0);
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
    
    vImage_Buffer buffer = { bitmap, height, width, bytesPerRow };

    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);
    
    return buffer;
}

- (vImage_Buffer)newBufferForBuffer:(vImage_Buffer)buffer {
    size_t width = buffer.width;
    size_t height = buffer.height;
    size_t bytesPerRow = buffer.rowBytes;
    
    Pixel_8 *outData = (Pixel_8 *)malloc( bytesPerRow * height );
    vImage_Buffer newBuffer = { outData, height, width, bytesPerRow };
    
    return newBuffer;
}

#pragma mark - Helper Methods

- (CGFloat)radiansFromDegrees:(CGFloat)degrees {
    return degrees * 2.0f * M_PI / 360.0f;
}