How can I prevent WPF from clipping my image?

Question

I am writing a WPF app that displays an image that is initially centered. The user can zoom in/out and move the image, which are implemented using ScaleTransform and TranslateTransform. That works great.

The problem is when the image is significantly bigger than the window, and the user moves the image or zooms out enough so that the entire image should be visible. The portion of the image that was originally hidden isn't rendered, and instead only the originally viewable part of the image is drawn.

Based on some other questions, if I put my image inside of a Canvas that will cause the entire image to be rendered, and when moved it will be rendered correctly. The problem is that I don't want my image to be in a Canvas, since that prevents any other layout from occurring - the HorizontalAlignment and VerticalAlignment properties are ignored (so the image is no longer centered), and I need to implement an option that will draw the image as large as possible to fill the entire area of the window which no longer works (setting the Stretch property to UniformToFill doesn't do anything).

Currently the two transforms are set to the RenderTransform property. If I use LayoutTransform instead, the entire image is drawn, but this also prevents the user from moving any portion of the image off the edge of the window (which is behavior that I would like to keep).

How can I tell WPF to always render the entire image without using a Canvas or a LayoutTransform?

Answer 1

I suggest not using a TranslateTransform but instead rely on the ScrollViewer.

<ScrollViewer>
   <Grid>
      <Image Source="blabla">
          <Image.LayoutTransform>
              <ScaleTransform />
          </Image.LayoutTransform>
      </Image>
   </Grid>
</ScrollViewer>

The ScrollViewer gives the Image infinite space to expand, the entire image will be rendered. The Grid forces a centered layout while still allowing the image to expand. If you don't like the scrollbars to control the translate then you can hide them and roll your own solution.

LayoutTransform is definetely the way to go, so that the image's actual size in pixels (based on the zoom) is properly reflected onto your window.