UWP / C# Rotating BMP

Question

The question seems to be asked already, however I cannot find a relevant answer.

I am loading a BMP image to memory in a UWP app, and I would like to rotate it by either 90, 180 or 270, but I just cannot find the way to do this.

The imgSource.rotate() does not seem to exist anymore The RotateTransform works with xaml ....

Could anyone add the missing code by a chance please?

public async Task LoadImage()
    {
        StorageFile file = await ApplicationData.Current.LocalFolder.GetFileAsync("test.bmp");
        using (var stream = await file.OpenAsync(FileAccessMode.Read))
        {
            var decoder = await BitmapDecoder.CreateAsync(stream);
            bitmap = await decoder.GetSoftwareBitmapAsync(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied);
            var imgSource = new WriteableBitmap(bitmap.PixelWidth, bitmap.PixelHeight);

            // Code to rotate image by 180 to be added

            bitmap.CopyToBuffer(imgSource.PixelBuffer);
        }
    }

Chela

Answer 1

The RotateTransform works with xaml

As you known, RotateTransform is for rotate transform in uwp app XAML. A RotateTransform is defined by an Angle that rotates an object through an arc around the point CenterX, CenterY. But a transform is typically used to fill the UIElement.RenderTransform property, so if you load the image source to an ImageControl, you can rotate the ImageControl since it is a UIElement. For example, if we have ImageControl as follows:

<Image x:Name="PreviewImage" Height="400" Width="300" AutomationProperties.Name="Preview of the image"  Stretch="Uniform" HorizontalAlignment="Center" VerticalAlignment="Center"/> 

We can simply rotate it by angle property by code as:

RotateTransform m_transform = new RotateTransform(); 
PreviewImage.RenderTransform = m_transform;
m_transform.Angle = 180;

If you need rotate an image file not a UIElement, you may need to decode the image file as what you already did and then encode the file with setting the BitmapTransform.Rotation property. Code as follows:

  double m_scaleFactor;
  private async void btnrotatefile_Click(object sender, RoutedEventArgs e)
  {
      StorageFile file = await ApplicationData.Current.LocalFolder.GetFileAsync("test.bmp"); 
      using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.ReadWrite),
                                         memStream = new InMemoryRandomAccessStream())
      {
          BitmapDecoder decoder = await BitmapDecoder.CreateAsync(fileStream); 
          uint originalWidth = decoder.PixelWidth;
          uint originalHeight = decoder.PixelHeight;
          BitmapEncoder encoder = await BitmapEncoder.CreateForTranscodingAsync(memStream, decoder);
          if (m_scaleFactor != 1.0)
          {
              encoder.BitmapTransform.ScaledWidth = (uint)(originalWidth * m_scaleFactor);
              encoder.BitmapTransform.ScaledHeight = (uint)(originalHeight * m_scaleFactor);
              encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Fant;
          }

         //Rotate 180
          encoder.BitmapTransform.Rotation = BitmapRotation.Clockwise180Degrees;
          await encoder.FlushAsync(); 
          memStream.Seek(0);
          fileStream.Seek(0);
          fileStream.Size = 0;
          await RandomAccessStream.CopyAsync(memStream, fileStream);
      }
  }

More features about the image file rotation you can use other APIS under Windows.Graphics.Imaging namespace. And the scenario 2 of SimpleImaging official sample provides a complete sample about image rotation you can reference.

Kaiserism

This is fantastic, works as expected. Indeed scenario 2 was the one needed. Thank you so much Sunteen. – Chela

This solution is great! However, do you have any idea how it can be done only with XAML definitions and bindings? (You may see more details in my question here: https://mcmap.net/q/473139/-uwp-rotating-an-image-while-keeping-it-aligned-to-the-grid-using-xaml-only/997940) – Abbatial