Backends: GLFW/SDL2/SDL3: Update monitors and work areas information every frame, as the later may change regardless of monitor changes. (#8415)

backends/imgui_impl_glfw.cpp

@@ -30,6 +30,7 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2025-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  2025-02-21: [Docking] Update monitors and work areas information every frame, as the later may change regardless of monitor changes. (#8415)
 //  2024-11-05: [Docking] Added Linux workaround for spurious mouse up events emitted while dragging and creating new viewport. (#3158, #7733, #7922)
 //  2024-08-22: moved some OS/backend related function pointers from ImGuiIO to ImGuiPlatformIO:
 //               - io.GetClipboardTextFn    -> platform_io.Platform_GetClipboardTextFn
@@ -180,7 +181,6 @@ struct ImGui_ImplGlfw_Data
     GLFWwindow*             KeyOwnerWindows[GLFW_KEY_LAST];
     bool                    InstalledCallbacks;
     bool                    CallbacksChainForAllWindows;
-    bool                    WantUpdateMonitors;
 #ifdef EMSCRIPTEN_USE_EMBEDDED_GLFW3
     const char*             CanvasSelector;
 #endif
@@ -519,8 +519,7 @@ void ImGui_ImplGlfw_CharCallback(GLFWwindow* window, unsigned int c)
 
 void ImGui_ImplGlfw_MonitorCallback(GLFWmonitor*, int)
 {
-    ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
-    bd->WantUpdateMonitors = true;
+    // This function is technically part of the API even if we stopped using the callback, so leaving it around.
 }
 
 #ifdef EMSCRIPTEN_USE_EMBEDDED_GLFW3
@@ -627,7 +626,6 @@ static bool ImGui_ImplGlfw_Init(GLFWwindow* window, bool install_callbacks, Glfw
 
     bd->Window = window;
     bd->Time = 0.0;
-    bd->WantUpdateMonitors = true;
 
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
     platform_io.Platform_SetClipboardTextFn = [](ImGuiContext*, const char* text) { glfwSetClipboardString(nullptr, text); };
@@ -910,9 +908,7 @@ static void ImGui_ImplGlfw_UpdateGamepads()
 
 static void ImGui_ImplGlfw_UpdateMonitors()
 {
-    ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
-    bd->WantUpdateMonitors = false;
 
     int monitors_count = 0;
     GLFWmonitor** glfw_monitors = glfwGetMonitors(&monitors_count);
@@ -966,8 +962,7 @@ void ImGui_ImplGlfw_NewFrame()
     io.DisplaySize = ImVec2((float)w, (float)h);
     if (w > 0 && h > 0)
         io.DisplayFramebufferScale = ImVec2((float)display_w / (float)w, (float)display_h / (float)h);
-    if (bd->WantUpdateMonitors)
-        ImGui_ImplGlfw_UpdateMonitors();
+    ImGui_ImplGlfw_UpdateMonitors();
 
     // Setup time step
     // (Accept glfwGetTime() not returning a monotonically increasing value. Seems to happens on disconnecting peripherals and probably on VMs and Emscripten, see #6491, #6189, #6114, #3644)

backends/imgui_impl_sdl2.cpp

@@ -26,6 +26,7 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2025-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  2025-02-21: [Docking] Update monitors and work areas information every frame, as the later may change regardless of monitor changes. (#8415)
 //  2025-02-10: Using SDL_OpenURL() in platform_io.Platform_OpenInShellFn handler.
 //  2025-01-20: Made ImGui_ImplSDL2_SetGamepadMode(ImGui_ImplSDL2_GamepadMode_Manual) accept an empty array.
 //  2024-10-24: Emscripten: from SDL 2.30.9, SDL_EVENT_MOUSE_WHEEL event doesn't require dividing by 100.0f.
@@ -144,7 +145,6 @@ struct ImGui_ImplSDL2_Data
     Uint64                  Time;
     char*                   ClipboardTextData;
     bool                    UseVulkan;
-    bool                    WantUpdateMonitors;
 
     // Mouse handling
     Uint32                  MouseWindowID;
@@ -436,15 +436,6 @@ bool ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event)
             io.SetKeyEventNativeData(key, event->key.keysym.sym, event->key.keysym.scancode, event->key.keysym.scancode); // To support legacy indexing (<1.87 user code). Legacy backend uses SDLK_*** as indices to IsKeyXXX() functions.
             return true;
         }
-#if SDL_HAS_DISPLAY_EVENT
-        case SDL_DISPLAYEVENT:
-        {
-            // 2.0.26 has SDL_DISPLAYEVENT_CONNECTED/SDL_DISPLAYEVENT_DISCONNECTED/SDL_DISPLAYEVENT_ORIENTATION,
-            // so change of DPI/Scaling are not reflected in this event. (SDL3 has it)
-            bd->WantUpdateMonitors = true;
-            return true;
-        }
-#endif
         case SDL_WINDOWEVENT:
         {
             ImGuiViewport* viewport = ImGui_ImplSDL2_GetViewportForWindowID(event->window.windowID);
@@ -862,10 +853,8 @@ static void ImGui_ImplSDL2_UpdateGamepads()
 // FIXME: Note that doesn't update with DPI/Scaling change only as SDL2 doesn't have an event for it (SDL3 has).
 static void ImGui_ImplSDL2_UpdateMonitors()
 {
-    ImGui_ImplSDL2_Data* bd = ImGui_ImplSDL2_GetBackendData();
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
     platform_io.Monitors.resize(0);
-    bd->WantUpdateMonitors = false;
     int display_count = SDL_GetNumVideoDisplays();
     for (int n = 0; n < display_count; n++)
     {
@@ -921,8 +910,7 @@ void ImGui_ImplSDL2_NewFrame()
         io.DisplayFramebufferScale = ImVec2((float)display_w / w, (float)display_h / h);
 
     // Update monitors
-    if (bd->WantUpdateMonitors)
-        ImGui_ImplSDL2_UpdateMonitors();
+    ImGui_ImplSDL2_UpdateMonitors();
 
     // Setup time step (we don't use SDL_GetTicks() because it is using millisecond resolution)
     // (Accept SDL_GetPerformanceCounter() not returning a monotonically increasing value. Happens in VMs and Emscripten, see #6189, #6114, #3644)

backends/imgui_impl_sdl3.cpp

@@ -24,6 +24,7 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2025-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  2025-02-21: [Docking] Update monitors and work areas information every frame, as the later may change regardless of monitor changes. (#8415)
 //  2025-02-10: Using SDL_OpenURL() in platform_io.Platform_OpenInShellFn handler.
 //  2025-01-20: Made ImGui_ImplSDL3_SetGamepadMode(ImGui_ImplSDL3_GamepadMode_Manual) accept an empty array.
 //  2024-10-24: Emscripten: SDL_EVENT_MOUSE_WHEEL event doesn't require dividing by 100.0f on Emscripten.
@@ -99,7 +100,6 @@ struct ImGui_ImplSDL3_Data
     Uint64                  Time;
     char*                   ClipboardTextData;
     bool                    UseVulkan;
-    bool                    WantUpdateMonitors;
 
     // IME handling
     SDL_Window*             ImeWindow;
@@ -400,15 +400,6 @@ bool ImGui_ImplSDL3_ProcessEvent(const SDL_Event* event)
             io.SetKeyEventNativeData(key, event->key.key, event->key.scancode, event->key.scancode); // To support legacy indexing (<1.87 user code). Legacy backend uses SDLK_*** as indices to IsKeyXXX() functions.
             return true;
         }
-        case SDL_EVENT_DISPLAY_ORIENTATION:
-        case SDL_EVENT_DISPLAY_ADDED:
-        case SDL_EVENT_DISPLAY_REMOVED:
-        case SDL_EVENT_DISPLAY_MOVED:
-        case SDL_EVENT_DISPLAY_CONTENT_SCALE_CHANGED:
-        {
-            bd->WantUpdateMonitors = true;
-            return true;
-        }
         case SDL_EVENT_WINDOW_MOUSE_ENTER:
         {
             if (ImGui_ImplSDL3_GetViewportForWindowID(event->window.windowID) == nullptr)
@@ -824,10 +815,8 @@ static void ImGui_ImplSDL3_UpdateGamepads()
 
 static void ImGui_ImplSDL3_UpdateMonitors()
 {
-    ImGui_ImplSDL3_Data* bd = ImGui_ImplSDL3_GetBackendData();
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
     platform_io.Monitors.resize(0);
-    bd->WantUpdateMonitors = false;
 
     int display_count;
     SDL_DisplayID* displays = SDL_GetDisplays(&display_count);
@@ -872,8 +861,7 @@ void ImGui_ImplSDL3_NewFrame()
         io.DisplayFramebufferScale = ImVec2((float)display_w / w, (float)display_h / h);
 
     // Update monitors
-    if (bd->WantUpdateMonitors)
-        ImGui_ImplSDL3_UpdateMonitors();
+    ImGui_ImplSDL3_UpdateMonitors();
 
     // Setup time step (we don't use SDL_GetTicks() because it is using millisecond resolution)
     // (Accept SDL_GetPerformanceCounter() not returning a monotonically increasing value. Happens in VMs and Emscripten, see #6189, #6114, #3644)

docs/CHANGELOG.txt

@@ -99,6 +99,8 @@ Docking+Viewports Branch:
 
 - Viewports: fixed an assert when a window load settings with a position outside
   monitor bounds, when there are multiple monitors. (#8393, #8385) [@gaborodriguez]
+- Backends: GLFW, SDL2/SDL3: Update monitors and work areas information every frame,
+  as the later may change regardless of monitor/display changes. (#8415)
 - Backends: Win32: WM_SETTINGCHANGE's SPI_SETWORKAREA message also triggers a refresh
   of monitor list, as they contain work area information. (#8415) [@PathogenDavid, @lailoken]