Backends: Win32: Fixed an issue where externally losing mouse capture (due to e.g. focus loss) would fail to claim it again the next subsequent click. (#8594)

backends/imgui_impl_win32.cpp

@@ -21,6 +21,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-04-30: Inputs: Fixed an issue where externally losing mouse capture (due to e.g. focus loss) would fail to claim it again the next subsequent click. (#8594)
 //  2025-03-10: When dealing with OEM keys, use scancodes instead of translated keycodes to choose ImGuiKey values. (#7136, #7201, #7206, #7306, #7670, #7672, #8468)
 //  2025-02-18: Added ImGuiMouseCursor_Wait and ImGuiMouseCursor_Progress mouse cursor support.
 //  2024-07-08: Inputs: Fixed ImGuiMod_Super being mapped to VK_APPS instead of VK_LWIN||VK_RWIN. (#7768)
@@ -682,7 +683,10 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandlerEx(HWND hwnd, UINT msg, WPA
         if (msg == WM_RBUTTONDOWN || msg == WM_RBUTTONDBLCLK) { button = 1; }
         if (msg == WM_MBUTTONDOWN || msg == WM_MBUTTONDBLCLK) { button = 2; }
         if (msg == WM_XBUTTONDOWN || msg == WM_XBUTTONDBLCLK) { button = (GET_XBUTTON_WPARAM(wParam) == XBUTTON1) ? 3 : 4; }
-        if (bd->MouseButtonsDown == 0 && ::GetCapture() == nullptr)
+        HWND hwnd_with_capture = ::GetCapture();
+        if (bd->MouseButtonsDown != 0 && hwnd_with_capture != hwnd) // Did we externally lost capture?
+            bd->MouseButtonsDown = 0;
+        if (bd->MouseButtonsDown == 0 && hwnd_with_capture == nullptr)
             ::SetCapture(hwnd); // Allow us to read mouse coordinates when dragging mouse outside of our window bounds.
         bd->MouseButtonsDown |= 1 << button;
         io.AddMouseSourceEvent(mouse_source);

docs/CHANGELOG.txt

@@ -100,6 +100,8 @@ Other changes:
   of WantVisible. This is set in the same structure because activating text input generally
   requires providing a window to the backend. (#8584, #6341)
 - Misc: added extra operators to ImVec4 in IMGUI_DEFINE_MATH_OPERATORS block. (#8510) [@gan74]
+- Backends: Win32: Fixed an issue where externally losing mouse capture (due to e.g. focus loss)
+  would fail to claim it again the next subsequent click. (#8594)
 - Backends: SDL2, SDL3, OSX: Fill gamepad inputs and set ImGuiBackendFlags_HasGamepad
   regardless of ImGuiConfigFlags_NavEnableGamepad being set. (#8508)
 - Backends: SDL2, SDL3: don't attempt to call SDL_CaptureMouse() on drivers where we don't