GetWindowRect returning wrong coordinaties - wpf

Question

i'm developing VSTO add-in for outlook which includes overlay on top of the window.
I'm building my UI using WPF.
Problem is that when i'm trying to attach WPF Window ( merge left/top/width/height ) to outlook window when STARTING at scale more than 100% GetWindowsRect Returns wrong rectangle.
BUT when i'm starting application at 100% scale then change windows scale at runtime to whatever value everything is good and DPI Aware. Both cases ( starting and runtime ) GetDpiForWindow returns correct values which is...strange. DPI Awareness is set using SetThreadDpiAwareness when forms are created.
Can't get my head what's wrong :<. Any advises appreciated.
Code for attaching:
public void AttachTo(IntPtr src, AttachFlagEnum flags)
{
var nativeRectangle = new WinAPI.RECT();
if (!WinAPI.GetWindowRect(src, ref nativeRectangle))
{
// throw new Win32Exception(Marshal.GetLastWin32Error());
return;
}
AttachToCoords(new Rectangle(nativeRectangle.Left, nativeRectangle.Top, nativeRectangle.Right - nativeRectangle.Left, nativeRectangle.Bottom - nativeRectangle.Top), flags);
}
Form create code:
private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
StateManager.Init();
OutlookUtils.WaitOutlookLoading();
using (var ctx = new DPIContextBlock(WinAPI.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE))
{
new Forms.One().Show();
new Forms.Overlay().Show();
new Forms.Two();
}
}
Overlay attach code (executes by timer )
private void OverlayThink(object ob)
{
if (Managers.StateManager.OutlookState == OutlookStateEnum.MINIMIZED || Managers.StateManager.UiState == UIStateEnum.DESCWND)
{
if (this.IsVisible)
{
this.Dispatcher.Invoke(() => this.Hide());
}
return;
}
this.Dispatcher.Invoke(() => this.AttachTo(Utils.OutlookUtils.GetWordWindow(), AttachFlagEnum.OVERLAY));
this.Dispatcher.Invoke(() => this.Show());
}

Answer 1

My solution to the problem was that AttachToCoords method sets coords from GetWindowRect directly to Window.Left | Right | Top | Bottom. That's wrong because internally WPF positions it's elements in 96 DPI coordinate system. So i was need to convert it before assigning.
Solution:
private Rectangle TransformCoords(Rectangle coords)
{
var source = PresentationSource.FromVisual(this);
coords.X = (int)(coords.X / source.CompositionTarget.TransformToDevice.M11);
coords.Y = (int)(coords.Y / source.CompositionTarget.TransformToDevice.M22);
coords.Width = (int)(coords.Width / source.CompositionTarget.TransformToDevice.M11);
coords.Height = (int)(coords.Height / source.CompositionTarget.TransformToDevice.M22);
return coords;
}

Answer 2

WPF (as well as Windows forms) should be scaled automatically depending on the DPI value set on the system. There is no need to calculate the size and positions of the dialog window in Outlook add-ins.
Instead, you need to set up the form correctly to follow the DPI settings and set the window parent, so it will be displayed on top of the Outlook window.