IO, Backends: add io.AddFocusEvent(). Clear pressed keys after loosing input focus (#3532)

Amend/fix #2445, #2696, #3751, #4377

backends/imgui_impl_allegro5.cpp

@@ -16,6 +16,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2021-08-17: Calling io.AddFocusEvent() on ALLEGRO_EVENT_DISPLAY_SWITCH_OUT/ALLEGRO_EVENT_DISPLAY_SWITCH_IN events.
 //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
 //  2021-05-19: Renderer: Replaced direct access to ImDrawCmd::TextureId with a call to ImDrawCmd::GetTexID(). (will become a requirement)
 //  2021-02-18: Change blending equation to preserve alpha in output buffer.
@@ -390,6 +391,19 @@ bool ImGui_ImplAllegro5_ProcessEvent(ALLEGRO_EVENT* ev)
         if (ev->keyboard.display == bd->Display)
             io.KeysDown[ev->keyboard.keycode] = (ev->type == ALLEGRO_EVENT_KEY_DOWN);
         return true;
+    case ALLEGRO_EVENT_DISPLAY_SWITCH_OUT:
+        if (ev->display.source == bd->Display)
+            io.AddFocusEvent(false);
+        return true;
+    case ALLEGRO_EVENT_DISPLAY_SWITCH_IN:
+        if (ev->display.source == bd->Display)
+        {
+            io.AddFocusEvent(true);
+#if defined(ALLEGRO_UNSTABLE)
+            al_clear_keyboard_state(bd->Display);
+#endif
+        }
+        return true;
     }
     return false;
 }

backends/imgui_impl_glfw.cpp

@@ -16,7 +16,8 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
-//  2021-07-29: *BREAKING CHANGE*: Inputs: MousePos is correctly reported when the host platform window is hovered but not focused (using glfwSetCursorEnterCallback). If you called ImGui_ImplGlfw_InitXXX() with install_callbacks = false, you MUST install the glfwSetCursorEnterCallback() callback and the forward to the backend via ImGui_ImplGlfw_CursorEnterCallback().
+//  2021-08-17: *BREAKING CHANGE*: Now using glfwSetWindowFocusCallback() to calling io.AddFocusEvent(). If you called ImGui_ImplGlfw_InitXXX() with install_callbacks = false, you MUST install glfwSetWindowFocusCallback() and forward it to the backend via ImGui_ImplGlfw_WindowFocusCallback().
+//  2021-07-29: *BREAKING CHANGE*: Now using glfwSetCursorEnterCallback(). MousePos is correctly reported when the host platform window is hovered but not focused. If you called ImGui_ImplGlfw_InitXXX() with install_callbacks = false, you MUST install glfwSetWindowFocusCallback() callback and forward it to the backend via ImGui_ImplGlfw_CursorEnterCallback().
 //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
 //  2020-01-17: Inputs: Disable error callback while assigning mouse cursors because some X11 setup don't have them and it generates errors.
 //  2019-12-05: Inputs: Added support for new mouse cursors added in GLFW 3.4+ (resizing cursors, not allowed cursor).
@@ -80,6 +81,7 @@ struct ImGui_ImplGlfw_Data
     bool                    InstalledCallbacks;
 
     // Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
+    GLFWwindowfocusfun      PrevUserCallbackWindowFocus;
     GLFWcursorenterfun      PrevUserCallbackCursorEnter;
     GLFWmousebuttonfun      PrevUserCallbackMousebutton;
     GLFWscrollfun           PrevUserCallbackScroll;
@@ -160,11 +162,22 @@ void ImGui_ImplGlfw_KeyCallback(GLFWwindow* window, int key, int scancode, int a
 #endif
 }
 
+void ImGui_ImplGlfw_WindowFocusCallback(GLFWwindow* window, int focused)
+{
+    ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
+    if (bd->PrevUserCallbackWindowFocus != NULL && window == bd->Window)
+        bd->PrevUserCallbackWindowFocus(window, focused);
+
+    ImGuiIO& io = ImGui::GetIO();
+    io.AddFocusEvent(focused != 0);
+}
+
 void ImGui_ImplGlfw_CursorEnterCallback(GLFWwindow* window, int entered)
 {
     ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
-    if (bd->PrevUserCallbackCursorEnter != NULL)
+    if (bd->PrevUserCallbackCursorEnter != NULL && window == bd->Window)
         bd->PrevUserCallbackCursorEnter(window, entered);
+
     if (entered)
         bd->MouseWindow = window;
     if (!entered && bd->MouseWindow == window)
@@ -256,6 +269,7 @@ static bool ImGui_ImplGlfw_Init(GLFWwindow* window, bool install_callbacks, Glfw
     glfwSetErrorCallback(prev_error_callback);
 
     // Chain GLFW callbacks: our callbacks will call the user's previously installed callbacks, if any.
+    bd->PrevUserCallbackWindowFocus = NULL;
     bd->PrevUserCallbackMousebutton = NULL;
     bd->PrevUserCallbackScroll = NULL;
     bd->PrevUserCallbackKey = NULL;
@@ -264,6 +278,7 @@ static bool ImGui_ImplGlfw_Init(GLFWwindow* window, bool install_callbacks, Glfw
     if (install_callbacks)
     {
         bd->InstalledCallbacks = true;
+        bd->PrevUserCallbackWindowFocus = glfwSetWindowFocusCallback(window, ImGui_ImplGlfw_WindowFocusCallback);
         bd->PrevUserCallbackCursorEnter = glfwSetCursorEnterCallback(window, ImGui_ImplGlfw_CursorEnterCallback);
         bd->PrevUserCallbackMousebutton = glfwSetMouseButtonCallback(window, ImGui_ImplGlfw_MouseButtonCallback);
         bd->PrevUserCallbackScroll = glfwSetScrollCallback(window, ImGui_ImplGlfw_ScrollCallback);
@@ -298,6 +313,7 @@ void ImGui_ImplGlfw_Shutdown()
 
     if (bd->InstalledCallbacks)
     {
+        glfwSetWindowFocusCallback(bd->Window, bd->PrevUserCallbackWindowFocus);
         glfwSetCursorEnterCallback(bd->Window, bd->PrevUserCallbackCursorEnter);
         glfwSetMouseButtonCallback(bd->Window, bd->PrevUserCallbackMousebutton);
         glfwSetScrollCallback(bd->Window, bd->PrevUserCallbackScroll);

backends/imgui_impl_glfw.h

@@ -32,6 +32,7 @@ IMGUI_IMPL_API void     ImGui_ImplGlfw_NewFrame();
 // GLFW callbacks
 // - When calling Init with 'install_callbacks=true': GLFW callbacks will be installed for you. They will call user's previously installed callbacks, if any.
 // - When calling Init with 'install_callbacks=false': GLFW callbacks won't be installed. You will need to call those function yourself from your own GLFW callbacks.
+IMGUI_IMPL_API void     ImGui_ImplGlfw_WindowFocusCallback(GLFWwindow* window, int focused);
 IMGUI_IMPL_API void     ImGui_ImplGlfw_CursorEnterCallback(GLFWwindow* window, int entered);
 IMGUI_IMPL_API void     ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow* window, int button, int action, int mods);
 IMGUI_IMPL_API void     ImGui_ImplGlfw_ScrollCallback(GLFWwindow* window, double xoffset, double yoffset);

backends/imgui_impl_osx.mm

@@ -19,6 +19,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2021-08-17: Calling io.AddFocusEvent() on NSApplicationDidBecomeActiveNotification/NSApplicationDidResignActiveNotification events.
 //  2021-06-23: Inputs: Added a fix for shortcuts using CTRL key instead of CMD key.
 //  2021-04-19: Inputs: Added a fix for keys remaining stuck in pressed state when CMD-tabbing into different application.
 //  2021-01-27: Inputs: Added a fix for mouse position not being reported when mouse buttons other than left one are down.
@@ -60,14 +61,24 @@ static void resetKeys()
 
 @interface ImFocusObserver : NSObject
 
+- (void)onApplicationBecomeActive:(NSNotification*)aNotification;
 - (void)onApplicationBecomeInactive:(NSNotification*)aNotification;
 
 @end
 
 @implementation ImFocusObserver
 
+- (void)onApplicationBecomeActive:(NSNotification*)aNotification
+{
+    ImGuiIO& io = ImGui::GetIO();
+    io.AddFocusEvent(true);
+}
+
 - (void)onApplicationBecomeInactive:(NSNotification*)aNotification
 {
+    ImGuiIO& io = ImGui::GetIO();
+    io.AddFocusEvent(false);
+
     // Unfocused applications do not receive input events, therefore we must manually
     // release any pressed keys when application loses focus, otherwise they would remain
     // stuck in a pressed state. https://github.com/ocornut/imgui/issues/3832
@@ -155,6 +166,10 @@ bool ImGui_ImplOSX_Init()
     };
 
     g_FocusObserver = [[ImFocusObserver alloc] init];
+    [[NSNotificationCenter defaultCenter] addObserver:g_FocusObserver
+                                             selector:@selector(onApplicationBecomeActive:)
+                                                 name:NSApplicationDidBecomeActiveNotification
+                                               object:nil];
     [[NSNotificationCenter defaultCenter] addObserver:g_FocusObserver
                                              selector:@selector(onApplicationBecomeInactive:)
                                                  name:NSApplicationDidResignActiveNotification

backends/imgui_impl_sdl.cpp

@@ -18,6 +18,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2021-08-17: Calling io.AddFocusEvent() on SDL_WINDOWEVENT_FOCUS_GAINED/SDL_WINDOWEVENT_FOCUS_LOST.
 //  2021-07-29: Inputs: MousePos is correctly reported when the host platform window is hovered but not focused (using SDL_GetMouseFocus() + SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH, requires SDL 2.0.5+)
 //  2021-06-29: *BREAKING CHANGE* Removed 'SDL_Window* window' parameter to ImGui_ImplSDL2_NewFrame() which was unnecessary.
 //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
@@ -148,6 +149,14 @@ bool ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event)
 #endif
             return true;
         }
+    case SDL_WINDOWEVENT:
+        {
+            if (event->window.event == SDL_WINDOWEVENT_FOCUS_GAINED)
+                io.AddFocusEvent(true);
+            else if (event->window.event == SDL_WINDOWEVENT_FOCUS_LOST)
+                io.AddFocusEvent(false);
+            return true;
+        }
     }
     return false;
 }

backends/imgui_impl_win32.cpp

@@ -33,7 +33,8 @@ typedef DWORD (WINAPI *PFN_XInputGetState)(DWORD, XINPUT_STATE*);
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
-//  2021-08-02: Inputs: Fixed keyboard modifiers being reported when host window doesn't have focus.
+//  2021-08-17: Calling io.AddFocusEvent() on WM_SETFOCUS/WM_KILLFOCUS messages.
+//  2021-08-02: Inputs: Fixed keyboard modifiers being reported when host windo doesn't have focus.
 //  2021-07-29: Inputs: MousePos is correctly reported when the host platform window is hovered but not focused (using TrackMouseEvent() to receive WM_MOUSELEAVE events).
 //  2021-06-29: Reorganized backend to pull data from a single structure to facilitate usage with multiple-contexts (all g_XXXX access changed to bd->XXXX).
 //  2021-06-08: Fixed ImGui_ImplWin32_EnableDpiAwareness() and ImGui_ImplWin32_GetDpiScaleForMonitor() to handle Windows 8.1/10 features without a manifest (per-monitor DPI, and properly calls SetProcessDpiAwareness() on 8.1).
@@ -431,9 +432,9 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
             io.KeyAlt = down;
         return 0;
     }
+    case WM_SETFOCUS:
     case WM_KILLFOCUS:
-        memset(io.KeysDown, 0, sizeof(io.KeysDown));
-        io.KeyCtrl = io.KeyShift = io.KeyAlt = io.KeySuper = false;
+        io.AddFocusEvent(msg == WM_SETFOCUS);
         return 0;
     case WM_CHAR:
         // You can also use ToAscii()+GetKeyboardState() to retrieve characters.

docs/CHANGELOG.txt

@@ -40,10 +40,13 @@ Breaking Changes:
 - Commented out redirecting functions/enums names that were marked obsolete in 1.67 and 1.69 (March 2019):
   - ImGui::GetOverlayDrawList() -> use ImGui::GetForegroundDrawList()
   - ImFont::GlyphRangesBuilder  -> use ImFontGlyphRangesBuilder
-- Backends: GLFW: backend now needs to use glfwSetCursorEnterCallback(). (#3751, #4377, #2445)
+- Backends: GLFW: backend now uses glfwSetCursorEnterCallback(). (#3751, #4377, #2445)
+- Backends: GLFW: backend now uses glfwSetWindowFocusCallback(). (#4388) [@thedmd]
   - If calling ImGui_ImplGlfw_InitXXX with install_callbacks=true: this is already done for you.
-  - If calling ImGui_ImplGlfw_InitXXX with install_callbacks=false: you WILL NEED to register the GLFW callback
-    with glfwSetCursorEnterCallback(), and forward events to the backend via ImGui_ImplGlfw_CursorEnterCallback().
+  - If calling ImGui_ImplGlfw_InitXXX with install_callbacks=false: you WILL NEED to register the GLFW callbacks
+    and forward them to the backend:
+    - Register glfwSetCursorEnterCallback, forward events to ImGui_ImplGlfw_CursorEnterCallback().
+    - Register glfwSetWindowFocusCallback, forward events to ImGui_ImplGlfw_WindowFocusCallback().
 - Backends: SDL2: removed unnecessary SDL_Window* parameter from ImGui_ImplSDL2_NewFrame(). (#3244) [@funchal]
   Kept inline redirection function (will obsolete).
 - Backends: SDL2: backend needs to set 'SDL_SetHint(SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH, "1")' in order to
@@ -56,6 +59,8 @@ Breaking Changes:
   return value of ButtonBehavior() rather than (HoveredId == id).
 
 Other Changes:
+- IO: Added io.AddFocusEvent() api for backend to tell when host window has gained/lost focus. (#4388) [@thedmd]
+  If you use a custom backend, consider adding support for this!
 - Windows: ImGuiWindowFlags_UnsavedDocument/ImGuiTabItmeFlags_UnsavedDocument display a dot instead of a '*' so it
   is independent from font style. When in a tab, the dot is displayed at the same position as the close button.
   Added extra comments to clarify the purpose of this flag in the context of docked windows.
@@ -101,6 +106,9 @@ Other Changes:
 - Backends: Win32: IME functions are disabled by default for non-Visual Studio compilers (MinGW etc.). Enable with
   '#define IMGUI_ENABLE_WIN32_DEFAULT_IME_FUNCTIONS' for those compilers. Undo change from 1.82. (#2590, #738, #4185, #4301)
 - Backends: Win32: Mouse position is correctly reported when the host window is hovered but not focused. (#2445, #2696, #3751, #4377)
+- Backends: Win32, SDL2, GLFW, OSX, Allegro: now calling io.AddFocusEvent() on focus gain/loss. (#4388) [@thedmd]
+  This allow us to ignore certain inputs on focus loss (previously relied on mouse loss but backends are now
+  reporting mouse even when host window is unfocused, as per #2445, #2696, #3751, #4377)
 - Backends: Fixed keyboard modifiers being reported when host window doesn't have focus. (#2622)
 - Backends: GLFW: Mouse position is correctly reported when the host window is hovered but not focused. (#3751, #4377, #2445)
   (backend now uses glfwSetCursorEnterCallback(). If you called ImGui_ImplGlfw_InitXXX with install_callbacks=false, you will

imgui.cpp

@@ -1180,6 +1180,22 @@ void ImGuiIO::ClearInputCharacters()
     InputQueueCharacters.resize(0);
 }
 
+void ImGuiIO::AddFocusEvent(bool focused)
+{
+    if (focused)
+        return;
+
+    // Clear buttons state when focus is lost
+    // (this is useful so e.g. releasing Alt after focus loss on Alt-Tab doesn't trigger the Alt menu toggle)
+    memset(KeysDown, 0, sizeof(KeysDown));
+    for (int n = 0; n < IM_ARRAYSIZE(KeysDownDuration); n++)
+        KeysDownDuration[n] = KeysDownDurationPrev[n] = -1.0f;
+    KeyCtrl = KeyShift = KeyAlt = KeySuper = false;
+    KeyMods = KeyModsPrev = ImGuiKeyModFlags_None;
+    for (int n = 0; n < IM_ARRAYSIZE(NavInputsDownDuration); n++)
+        NavInputsDownDuration[n] = NavInputsDownDurationPrev[n] = -1.0f;
+}
+
 //-----------------------------------------------------------------------------
 // [SECTION] MISC HELPERS/UTILITIES (Geometry functions)
 //-----------------------------------------------------------------------------
@@ -9694,8 +9710,9 @@ static void ImGui::NavUpdateWindowing()
             g.NavWindowingToggleLayer = false;
 
         // Apply layer toggle on release
-        // FIXME: We lack an explicit IO variable for "is the platform window focused", so compare mouse validity to detect the common case of backend clearing releases all keys on ALT-TAB
-        if (!io.KeyAlt && g.NavWindowingToggleLayer)
+        // Important: we don't assume that Alt was previously held in order to handle loss of focus when backend calls io.AddFocusEvent(false)
+        // Important: as before version <18314 we lacked an explicit IO event for focus gain/loss, we also compare mouse validity to detect old backends clearing mouse pos on focus loss.
+        if (!(io.KeyMods & ImGuiKeyModFlags_Alt) && (io.KeyModsPrev & ImGuiKeyModFlags_Alt) && g.NavWindowingToggleLayer)
             if (g.ActiveId == 0 || g.ActiveIdAllowOverlap)
                 if (IsMousePosValid(&io.MousePos) == IsMousePosValid(&io.MousePosPrev))
                     apply_toggle_layer = true;

imgui.h

@@ -61,7 +61,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.84 WIP"
-#define IMGUI_VERSION_NUM           18313
+#define IMGUI_VERSION_NUM           18314
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE
 
@@ -1868,6 +1868,7 @@ struct ImGuiIO
     IMGUI_API void  AddInputCharacterUTF16(ImWchar16 c);        // Queue new character input from an UTF-16 character, it can be a surrogate
     IMGUI_API void  AddInputCharactersUTF8(const char* str);    // Queue new characters input from an UTF-8 string
     IMGUI_API void  ClearInputCharacters();                     // Clear the text input buffer manually
+    IMGUI_API void  AddFocusEvent(bool focused);                // Notifies Dear ImGui when hosting platform windows lose or gain input focus
 
     //------------------------------------------------------------------
     // Output - Updated by NewFrame() or EndFrame()/Render()