From d8f7aac4ca32f3aee3fcdda3e2847489e847b60e Mon Sep 17 00:00:00 2001
From: Mike Griese <migrie@microsoft.com>
Date: Fri, 6 Mar 2020 16:14:35 -0600
Subject: [PATCH] Resize the drag bar on `WM_DISPLAYCHANGE` (#4829)

## Summary of the Pull Request

Pretty straightforward. When we get a `WM_DISPLAYCHANGE`, that means the
display's DPI changed. When that happens, resize the drag bar, so that
it'll reflect the new scaling.

Unblocks #4778
Closes #4166

## Validation
Man I've changed the DPI of my displays so many times in the last 30
minutes. I dragged the window across a bunch of DPI boundaries too.
---
 src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp b/src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp
index b4752bd7327..bf35c555aa6 100644
--- a/src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp
+++ b/src/cascadia/WindowsTerminal/NonClientIslandWindow.cpp
@@ -480,6 +480,11 @@ void NonClientIslandWindow::_UpdateFrameMargins() const noexcept
 {
     switch (message)
     {
+    case WM_DISPLAYCHANGE:
+        // GH#4166: When the DPI of the monitor changes out from underneath us,
+        // resize our drag bar, to reflect its newly scaled size.
+        _UpdateIslandRegion();
+        return 0;
     case WM_NCCALCSIZE:
         return _OnNcCalcSize(wParam, lParam);
     case WM_NCHITTEST: