Viewport: Comments about honoring ImGuiViewportFlags_NoInputs and MouseHoveredViewport. (#1542)

examples/imgui_impl_glfw.cpp

@@ -387,6 +387,10 @@ static LRESULT CALLBACK WndProcNoInputs(HWND hWnd, UINT msg, WPARAM wParam, LPAR
 {
     if (msg == WM_NCHITTEST)
     {
+        // Let mouse pass-through the window. This will allow the back-end to set io.MouseHoveredViewport properly (which is OPTIONAL).
+        // The ImGuiViewportFlags_NoInputs flag is set while dragging a viewport, as want to detect the window behind the one we are dragging.
+        // If you cannot easily access those viewport flags from your windowing/event code: you may manually synchronize its state e.g. in
+        // your main loop after calling UpdatePlatformWindows(). Iterate all viewports/platform windows and pass the flag to your windowing system.
         ImGuiViewport* viewport = (ImGuiViewport*)::GetPropA(hWnd, "IMGUI_VIEWPORT");
         if (viewport->Flags & ImGuiViewportFlags_NoInputs)
             return HTTRANSPARENT;

examples/imgui_impl_win32.cpp

@@ -503,7 +503,10 @@ static LRESULT CALLBACK ImGui_ImplWin32_WndProcHandler_PlatformWindow(HWND hWnd,
             viewport->PlatformRequestResize = true;
             break;
         case WM_NCHITTEST:
-            // Let mouse pass-through the window, this is used while e.g. dragging a window, we creates a temporary overlay but want the cursor to aim behind our overlay.
+            // Let mouse pass-through the window. This will allow the back-end to set io.MouseHoveredViewport properly (which is OPTIONAL).
+            // The ImGuiViewportFlags_NoInputs flag is set while dragging a viewport, as want to detect the window behind the one we are dragging.
+            // If you cannot easily access those viewport flags from your windowing/event code: you may manually synchronize its state e.g. in
+            // your main loop after calling UpdatePlatformWindows(). Iterate all viewports/platform windows and pass the flag to your windowing system.
             if (viewport->Flags & ImGuiViewportFlags_NoInputs)
                 return HTTRANSPARENT;
             break;

imgui.h

@@ -1079,7 +1079,7 @@ struct ImGuiIO
     float       MouseWheel;                     // Mouse wheel Vertical: 1 unit scrolls about 5 lines text. 
     float       MouseWheelH;                    // Mouse wheel Horizontal. Most users don't have a mouse with an horizontal wheel, may not be filled by all back-ends.
     ImGuiID     MousePosViewport;               // (Optional) When using multiple viewports: viewport from which io.MousePos is based from (when dragging this is generally the captured/focused viewport, even though we can drag outside of it and then it's not hovered anymore). (0 == default viewport)
-    ImGuiID     MouseHoveredViewport;           // (Optional) When using multiple viewports: viewport the OS mouse cursor is hovering. (0 == default viewport)
+    ImGuiID     MouseHoveredViewport;           // (Optional) When using multiple viewports: viewport the OS mouse cursor is hovering. (0 == default viewport) _IGNORING_ viewports with the ImGuiBackendFlags_HasMouseHoveredViewport flag, and _REGARDLESS_ of whether another viewport is focused. Set io.BackendFlags |= ImGuiBackendFlags_HasMouseHoveredViewport if you can provide this information.
     bool        MouseDrawCursor;                // Request ImGui to draw a mouse cursor for you (if you are on a platform without a mouse cursor).
     bool        KeyCtrl;                        // Keyboard modifier pressed: Control
     bool        KeyShift;                       // Keyboard modifier pressed: Shift