Issue #1606 - Add support for multi-monitor DPI awareness v2 (W10 1706+)

1 files changed, 15 insertions, 5 deletions

diff --git a/widget/windows/WinUtils.cpp b/widget/windows/WinUtils.cpp
index 28033193f..a43c92b69 100644
--- a/widget/windows/WinUtils.cpp
+++ b/widget/windows/WinUtils.cpp
@@ -449,10 +449,20 @@ WinUtils::Initialize()
   if (IsWin10OrLater()) {
     HMODULE user32Dll = ::GetModuleHandleW(L"user32");
     if (user32Dll) {
-      sEnableNonClientDpiScaling = (EnableNonClientDpiScalingProc)
-        ::GetProcAddress(user32Dll, "EnableNonClientDpiScaling");
-      sSetThreadDpiAwarenessContext = (SetThreadDpiAwarenessContextProc)
-        ::GetProcAddress(user32Dll, "SetThreadDpiAwarenessContext");
+      auto getThreadDpiAwarenessContext = (decltype(GetThreadDpiAwarenessContext)*)
+        ::GetProcAddress(user32Dll, "GetThreadDpiAwarenessContext");
+      auto areDpiAwarenessContextsEqual = (decltype(AreDpiAwarenessContextsEqual)*)
+        ::GetProcAddress(user32Dll, "AreDpiAwarenessContextsEqual");
+      if (getThreadDpiAwarenessContext && areDpiAwarenessContextsEqual &&
+          areDpiAwarenessContextsEqual(getThreadDpiAwarenessContext(),
+                                       DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE)) {
+        // Only per-monitor DPI awareness v1 requires these workarounds.
+        // Since this was introduced in Win 8.1 we'll need to keep this indefinitely.
+        sEnableNonClientDpiScaling = (EnableNonClientDpiScalingProc)
+          ::GetProcAddress(user32Dll, "EnableNonClientDpiScaling");
+        sSetThreadDpiAwarenessContext = (SetThreadDpiAwarenessContextProc)
+          ::GetProcAddress(user32Dll, "SetThreadDpiAwarenessContext");
+      }
     }
   }
 
@@ -468,7 +478,7 @@ LRESULT WINAPI
 WinUtils::NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
                                             WPARAM wParam, LPARAM lParam)
 {
-  if (msg == WM_NCCREATE && sEnableNonClientDpiScaling) {
+  if (msg == WM_NCCREATE) {
     sEnableNonClientDpiScaling(hWnd);
   }
   return ::DefWindowProcW(hWnd, msg, wParam, lParam);