旋转 UIImage 单点触控

Question

我正在尝试将图像从手机上传到我的网络服务，但我注意到上传图像时图像方向丢失了。在上传之前我需要做些什么来确保图像以正确的方向上传吗？

我还查看了其他地方并找到了用于旋转图像的 Objective-C 代码，我将其转换为 C#，但每次使用旋转方法时，图像都会变黑，即我猜什么都不会显示。

我附上我的代码供您参考，如果有人能告诉我我做错了什么，我将非常非常感激。谢谢！

    public static UIImage RotateImage(this UIImage image)
    {
        UIImage imageToReturn = null;
        if(image.Orientation == UIImageOrientation.Up)
        {
            imageToReturn = image;
        }
        else 
        {
            CGAffineTransform transform = CGAffineTransform.MakeIdentity();

            switch (image.Orientation) {
                case UIImageOrientation.Down:
                case UIImageOrientation.DownMirrored:
                    transform.Translate(image.Size.Width, image.Size.Height);
                    transform.Rotate((float)Math.PI);
                    break;

                case UIImageOrientation.Left:
                case UIImageOrientation.LeftMirrored:
                    transform.Translate(image.Size.Width, 0);
                    transform.Rotate((float)Math.PI/2);
                    break;

                case UIImageOrientation.Right:
                case UIImageOrientation.RightMirrored:
                    transform.Translate(0, image.Size.Height);
                    transform.Rotate((float)-Math.PI/2);
                    break;
                case UIImageOrientation.Up:
                case UIImageOrientation.UpMirrored:
                    break;
            }

            switch (image.Orientation) {
                case UIImageOrientation.UpMirrored:
                case UIImageOrientation.DownMirrored:
                    transform.Translate(image.Size.Width, 0);
                    transform.Scale(-1, 1);
                    break;

                case UIImageOrientation.LeftMirrored:
                case UIImageOrientation.RightMirrored:
                    transform.Translate(image.Size.Height, 0);
                    transform.Scale(-1, 1);
                    break;
                case UIImageOrientation.Up:
                case UIImageOrientation.Down:
                case UIImageOrientation.Left:
                case UIImageOrientation.Right:
                    break;
            }

            //now draw image
            using(var context = new CGBitmapContext(IntPtr.Zero,
                                                    (int)image.Size.Width, 
                                                    (int)image.Size.Height, 
                                                    image.CGImage.BitsPerComponent,
                                                    image.CGImage.BytesPerRow,
                                                    image.CGImage.ColorSpace,
                                                    image.CGImage.BitmapInfo)){
                context.ConcatCTM(transform);
                switch (image.Orientation) 
                {
                    case UIImageOrientation.Left:
                    case UIImageOrientation.LeftMirrored:
                    case UIImageOrientation.Right:
                    case UIImageOrientation.RightMirrored:
                        // Grr...
                        context.DrawImage(new RectangleF(PointF.Empty,new SizeF(image.Size.Height, image.Size.Width)), image.CGImage);
                        break;
                    default:
                        context.DrawImage(new RectangleF(PointF.Empty, new SizeF(image.Size.Width, image.Size.Height)), image.CGImage);
                        break;
                }

                using(var imageRef = context.ToImage())
                {
                    imageToReturn = new UIImage(imageRef);
                }
            }
        }

        return imageToReturn;
    }

Answer 1

你得到黑色图像的原因是 translate 和 rotate 调用是向后的。 iPod/iphone 上的正常人像图片是“右”方向。转换它们的正确代码使用：

        case UIImageOrientation.Right:
        case UIImageOrientation.RightMirrored:
            transform.Rotate (-(float)Math.PI / 2);
            transform.Translate (0, input.Size.Height);
            break;

变换函数是顺序相关的。此代码将其旋转到正确的方向，但由于旋转大约是左下角的 0,0 坐标，因此图像现在刚好离开框架的底部。然后翻译将它推到它所属的位置。

原始代码会将侧向图像推离框架顶部，然后旋转将转动物体，使图像向右转，但远离框架右侧。

使用较小的高度值（如 100 或 200 和 pi/4）将很容易显示更改这些函数的顺序时得到的差异，因为某些原始图像始终可见。

Answer 2

使用@Random 提供的信息，我更正了原始代码以使其正常工作：

    private byte[] RotateImage(UIImage image)
    {
        UIImage imageToReturn = null;
        if (image.Orientation == UIImageOrientation.Up)
        {
            imageToReturn = image;
        }
        else
        {
            CGAffineTransform transform = CGAffineTransform.MakeIdentity();

            switch (image.Orientation)
            {
                case UIImageOrientation.Down:
                case UIImageOrientation.DownMirrored:
                    transform.Rotate((float)Math.PI);
                    transform.Translate(image.Size.Width, image.Size.Height);
                    break;

                case UIImageOrientation.Left:
                case UIImageOrientation.LeftMirrored:
                    transform.Rotate((float)Math.PI / 2);
                    transform.Translate(image.Size.Width, 0);
                    break;

                case UIImageOrientation.Right:
                case UIImageOrientation.RightMirrored:
                    transform.Rotate(-(float)Math.PI / 2);
                    transform.Translate(0, image.Size.Height);
                    break;
                case UIImageOrientation.Up:
                case UIImageOrientation.UpMirrored:
                    break;
            }

            switch (image.Orientation)
            {
                case UIImageOrientation.UpMirrored:
                case UIImageOrientation.DownMirrored:
                    transform.Translate(image.Size.Width, 0);
                    transform.Scale(-1, 1);
                    break;

                case UIImageOrientation.LeftMirrored:
                case UIImageOrientation.RightMirrored:
                    transform.Translate(image.Size.Height, 0);
                    transform.Scale(-1, 1);
                    break;
                case UIImageOrientation.Up:
                case UIImageOrientation.Down:
                case UIImageOrientation.Left:
                case UIImageOrientation.Right:
                    break;
            }

            //now draw image
            using (var context = new CGBitmapContext(IntPtr.Zero,
                                                    (int)image.Size.Width,
                                                    (int)image.Size.Height,
                                                    image.CGImage.BitsPerComponent,
                                                    image.CGImage.BytesPerRow,
                                                    image.CGImage.ColorSpace,
                                                    image.CGImage.BitmapInfo))
            {
                context.ConcatCTM(transform);
                switch (image.Orientation)
                {
                    case UIImageOrientation.Left:
                    case UIImageOrientation.LeftMirrored:
                    case UIImageOrientation.Right:
                    case UIImageOrientation.RightMirrored:
                        // Grr...
                        context.DrawImage(new RectangleF(PointF.Empty, new SizeF((float)image.Size.Height, (float)image.Size.Width)), image.CGImage);
                        break;
                    default:
                        context.DrawImage(new RectangleF(PointF.Empty, new SizeF((float)image.Size.Width, (float)image.Size.Height)), image.CGImage);
                        break;
                }

                using (var imageRef = context.ToImage())
                {
                    imageToReturn = new UIImage(imageRef);
                }
            }
        }

        using (NSData imageData = imageToReturn.AsJPEG())
        {
            Byte[] byteArray = new Byte[imageData.Length];
            System.Runtime.InteropServices.Marshal.Copy(imageData.Bytes, byteArray, 0, Convert.ToInt32(imageData.Length));
            return byteArray;
        }
    }

非常有用的一段代码

Answer 3

我通过this question 找到了this gist。希望这段代码对你有用！