WPF MVVM binding controls with helper methods PDFTron PDFViewer - wpf

Question

I am struggling with a WPF MVVM problem using a control that has helper functions and exposing those helper functions to my viewmodels.
I am using the PDFTron viewer control that shows a PDFDocument object. Items in that PDFDocument are specified in terms of a PDFTron.Rect structure with the elements measured in points(1/72th inch) and a page number
To help convert the coordinate systems to and from screen position the PDFTron ViewerControl has various function on itself.
e.g. To convert from a screen point
Double x, y;
int page = Control.GetPageNumberFromScreenPt(x, y);
Control.ConvScreenPtToPagePt(ref x, ref y, page);
To convert to a screen point is from the object being examined
PDFTron.Rect r = Control.GetScreenRectForAnnot(embeddedObject, pageNumber);
What the best way of calling/exposing or binding to functions like this between the view model(s) and the PDF control as I would really like to databind to coordinates.
For instance I have an adorner defined in XAML that allows me to move an image I have read from the embeddedobject about the page by dragging and I can also resize the image. The viewmodel knows As my view model knows the image the embedded object its page and Rectangle on that page, but as PDF coordinates. But this needs to be translated to screen coordinates for the X, Y, Width and Height for binding to the XAML Attributes. I cannot quite see how to do this as it seems beyond a dataconverter.
So the control in the xaml has attributes measured in screen units
AdornerLeft="{Binding Data.X, Mode=TwoWay}"
AdornerTop="{Binding Data.Y, Mode=TwoWay}"
AdornerWidth="{Binding Data.Width, Mode=TwoWay}"
AdornerHeight="{Binding Data.Height, Mode=TwoWay}"
If the X and Y change I need the change to be reflected eventually as the page,x,y coordinates of the viewer as they are what are used by the underlying model.
I did wonder would it be wise to make a series of dependency properties so if I change one it ripples the change through the others as a conversion? So for example I have a property ScreenY When that changes it updates PDFY and PDFPage and vice versa but that seems overly complicated. Any suggestions?

Answer 1

Typically what is done, is that during user interaction, so while your user is moving and resizing the image, everything is drawn overtop of PDFViewWPF viewer.
You can get a Canvas object from PDFViewWPF.GetCanvas() and then you can draw your image on that if you like.
At this point, nothing relates to the PDF, you are just dealing with WPF coordinates.
Only once the user is done moving and dragging, and you want to add the image to the PDF page, perhaps as a Stamp annotation, or even injecting the image into the page content, only then would you erase all your graphics, and inject the image into the PDF. Only at this point would you need to translate between coordinate systems.
Please take a closer look at the PDFViewWPFTools project, and see how something like the Rectangle annotations are created.
This post might provide additional clarity for you.

Answer 2

I ended up using the Prism library and the eventAggregator to pass the details back to a the View and get the results, also using events to refresh the view. The PDFWPFViewer MVVM sample from PdfTron beside having some issues with incorrect bindings, essentially uses a tool library that is shared and acts like a windows forms library, no behaviors for controlling adorner drag etc.