Mouse event handling of Handles is off

For editing custom assets, I am rendering a little preview scene using a PreviewRenderUtility in an EditorWindow and I'd like it support handles for convenient position editing.

This is a rough outline of my code (which is ultimately called during the window's OnGUI):

Code (CSharp):

1. // begin preview
2. _previewRenderUtility.BeginPreview(rect, GUIStyle.none);
3.  
4. /* ... render the scene ... */
5.  
6. // do handles
7. Handles.SetCamera(_previewRenderUtility.camera);
8. editPos = Handles.PositionHandle(editPos, Quaternion.identity);
9.  
10. // finalize preview
11. _previewRenderUtility.EndAndDrawPreview(rect);

rect is the rectangle of the GUI the preview is using.

The position handle is rendered at the correct position and looks fine. However, it's processing mouse input in a wrong way: the detected mouse position is off. In order to select the handle, I have to move the mouse somewhere above and left of it.

So there seems to be some discrepancy between Handles' screen-to-world position conversion and the preview's world-to-screen rendering, with the latter being correct. I feel like I need to tell Handles what part of the screen I'm using, but the variant of Handles.SetCamera that takes a rectangle is not documented and I couldn't get it to work properly.

Does anybody know what I need to do here?

 

Quick and dirty solution: modify mousePosition in Event.current to account for the discrepancy.

 

I tried that, but that's not as quick as it seems because perspective is involved, and I believe getting this right is harder than a clean solution...