From fbfd7e65c842c7909b11747f0641364593304f1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Camilla=20L=C3=B6wy?= <elmindreda@elmindreda.org>
Date: Wed, 1 Dec 2021 17:55:16 +0100
Subject: [PATCH] Win32: Fix bad content scale on monitor disconnect

The monitor handle could have become invalid just before the call to
GetDpiForMonitor.  It was possible for both window and monitor content
scale queries.

This ensures both that an appropriate error is emitted and that the
retrieved values are zero on error.

Fixes #1615
---
 CONTRIBUTORS.md     |  1 +
 README.md           |  3 +++
 src/win32_monitor.c | 13 ++++++++++++-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 959b55eb..d86fe473 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -62,6 +62,7 @@ video tutorials.
  - Mário Freitas
  - GeO4d
  - Marcus Geelnard
+ - ghuser404
  - Charles Giessen
  - Ryan C. Gordon
  - Stephen Gowen
diff --git a/README.md b/README.md
index b13739f1..e3f7d9e7 100644
--- a/README.md
+++ b/README.md
@@ -202,6 +202,9 @@ information on what to include when reporting a bug.
    later (#1783,#1796)
  - [Win32] Bugfix: Compilation with LLVM for Windows failed (#1807,#1824,#1874)
  - [Win32] Bugfix: The foreground lock timeout was overridden, ignoring the user
+ - [Win32] Bugfix: Content scale queries could fail silently (#1615)
+ - [Win32] Bugfix: Content scales could have garbage values if monitor was recently
+   disconnected (#1615)
  - [Cocoa] Added support for `VK_EXT_metal_surface` (#1619)
  - [Cocoa] Added locating the Vulkan loader at runtime in an application bundle
  - [Cocoa] Moved main menu creation to GLFW initialization time (#1649)
diff --git a/src/win32_monitor.c b/src/win32_monitor.c
index 17359a5f..cdee49a9 100644
--- a/src/win32_monitor.c
+++ b/src/win32_monitor.c
@@ -317,8 +317,19 @@ void _glfwGetHMONITORContentScaleWin32(HMONITOR handle, float* xscale, float* ys
 {
     UINT xdpi, ydpi;
 
+    if (xscale)
+        *xscale = 0.f;
+    if (yscale)
+        *yscale = 0.f;
+
     if (IsWindows8Point1OrGreater())
-        GetDpiForMonitor(handle, MDT_EFFECTIVE_DPI, &xdpi, &ydpi);
+    {
+        if (GetDpiForMonitor(handle, MDT_EFFECTIVE_DPI, &xdpi, &ydpi) != S_OK)
+        {
+            _glfwInputError(GLFW_PLATFORM_ERROR, "Win32: Failed to query monitor DPI");
+            return;
+        }
+    }
     else
     {
         const HDC dc = GetDC(NULL);