Backends: Win32: Fixed setting of io.DisplaySize to invalid/uninitialized data when after hwnd has been closed.

GetClientRect() fails on closed hwnd which left the rectangle uninitialized and copied to DisplaySize. Ensure it is zero + similar failsafe in io.WantSetMousePos path.

backends/imgui_impl_win32.cpp

@@ -32,6 +32,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2020-12-04: Misc: Fixed setting of io.DisplaySize to invalid/uninitialized data when after hwnd has been closed.
 //  2020-03-03: Inputs: Calling AddInputCharacterUTF16() to support surrogate pairs leading to codepoint >= 0x10000 (for more complete CJK inputs)
 //  2020-02-17: Added ImGui_ImplWin32_EnableDpiAwareness(), ImGui_ImplWin32_GetDpiScaleForHwnd(), ImGui_ImplWin32_GetDpiScaleForMonitor() helper functions.
 //  2020-01-14: Inputs: Added support for #define IMGUI_IMPL_WIN32_DISABLE_GAMEPAD/IMGUI_IMPL_WIN32_DISABLE_LINKING_XINPUT.
@@ -153,7 +154,7 @@ static void ImGui_ImplWin32_UpdateMousePos()
     if (io.WantSetMousePos)
     {
         POINT pos = { (int)io.MousePos.x, (int)io.MousePos.y };
-        ::ClientToScreen(g_hWnd, &pos);
+        if (::ClientToScreen(g_hWnd, &pos))
             ::SetCursorPos(pos.x, pos.y);
     }
 
@@ -221,12 +222,12 @@ void    ImGui_ImplWin32_NewFrame()
     IM_ASSERT(io.Fonts->IsBuilt() && "Font atlas not built! It is generally built by the renderer backend. Missing call to renderer _NewFrame() function? e.g. ImGui_ImplOpenGL3_NewFrame().");
 
     // Setup display size (every frame to accommodate for window resizing)
-    RECT rect;
+    RECT rect = { 0, 0, 0, 0 };
     ::GetClientRect(g_hWnd, &rect);
     io.DisplaySize = ImVec2((float)(rect.right - rect.left), (float)(rect.bottom - rect.top));
 
     // Setup time step
-    INT64 current_time;
+    INT64 current_time = 0;
     ::QueryPerformanceCounter((LARGE_INTEGER*)&current_time);
     io.DeltaTime = (float)(current_time - g_Time) / g_TicksPerSecond;
     g_Time = current_time;

docs/CHANGELOG.txt

@@ -94,6 +94,7 @@ Other Changes:
   when the later returns zero (e.g. Desktop GL 2.x). (#3530) [@xndcn]
 - Backends: OpenGL3: Backup and restore GL_PRIMITIVE_RESTART state. (#3544) [@Xipiryon]
 - Backends: Vulkan: Added support for specifying which subpass to reference during VkPipeline creation. (@3579) [@bdero]
+- Backends: Win32: Fix setting of io.DisplaySize to invalid/uninitialized data after hwnd has been closed.
 - Backends: OSX: Fix keypad-enter key not working on MacOS. (#3554) [@rokups, @lfnoise]
 - Examples: Apple+Metal: Consolidated/simplified to get closer to other examples. (#3543) [@warrenm]
 - Examples: Apple+Metal: Forward events down so OS key combination like Cmd+Q can work. (#3554) [@rokups]