Backends: GLFW: Linux workaround for spurious mouse up events emitted while dragging and creating new viewport. (#3158, #7733, #7922)

Initially suggested by rokups. Rewrote for recent backends with a few tweaks to accomodate for variable WM unfocus timing.

backends/imgui_impl_glfw.cpp

@@ -29,6 +29,7 @@
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
 //  2024-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
+//  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
 //               - io.SetClipboardTextFn    -> platform_io.Platform_SetClipboardTextFn
@@ -172,6 +173,8 @@ struct ImGui_ImplGlfw_Data
     double                  Time;
     GLFWwindow*             MouseWindow;
     GLFWcursor*             MouseCursors[ImGuiMouseCursor_COUNT];
+    bool                    MouseIgnoreButtonUpWaitForFocusLoss;
+    bool                    MouseIgnoreButtonUp;
     ImVec2                  LastValidMousePos;
     GLFWwindow*             KeyOwnerWindows[GLFW_KEY_LAST];
     bool                    InstalledCallbacks;
@@ -367,6 +370,10 @@ void ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow* window, int button, int acti
     if (bd->PrevUserCallbackMousebutton != nullptr && ImGui_ImplGlfw_ShouldChainCallback(window))
         bd->PrevUserCallbackMousebutton(window, button, action, mods);
 
+    // Workaround for Linux: ignore mouse up events which are following an focus loss following a viewport creation
+    if (bd->MouseIgnoreButtonUp && action == GLFW_RELEASE)
+        return;
+
     ImGui_ImplGlfw_UpdateKeyModifiers(window);
 
     ImGuiIO& io = ImGui::GetIO();
@@ -451,6 +458,10 @@ void ImGui_ImplGlfw_WindowFocusCallback(GLFWwindow* window, int focused)
     if (bd->PrevUserCallbackWindowFocus != nullptr && ImGui_ImplGlfw_ShouldChainCallback(window))
         bd->PrevUserCallbackWindowFocus(window, focused);
 
+    // Workaround for Linux: when losing focus with MouseIgnoreButtonUpWaitForFocusLoss set, we will temporarily ignore subsequent Mouse Up events
+    bd->MouseIgnoreButtonUp = (bd->MouseIgnoreButtonUpWaitForFocusLoss && focused == 0);
+    bd->MouseIgnoreButtonUpWaitForFocusLoss = false;
+
     ImGuiIO& io = ImGui::GetIO();
     io.AddFocusEvent(focused != 0);
 }
@@ -965,6 +976,7 @@ void ImGui_ImplGlfw_NewFrame()
     io.DeltaTime = bd->Time > 0.0 ? (float)(current_time - bd->Time) : (float)(1.0f / 60.0f);
     bd->Time = current_time;
 
+    bd->MouseIgnoreButtonUp = false;
     ImGui_ImplGlfw_UpdateMouseData();
     ImGui_ImplGlfw_UpdateMouseCursor();
 
@@ -1104,6 +1116,11 @@ static void ImGui_ImplGlfw_CreateWindow(ImGuiViewport* viewport)
     ImGui_ImplGlfw_ViewportData* vd = IM_NEW(ImGui_ImplGlfw_ViewportData)();
     viewport->PlatformUserData = vd;
 
+    // Workaround for Linux: ignore mouse up events corresponding to losing focus of the previously focused window (#7733, #3158, #7922)
+#ifdef __linux__
+    bd->MouseIgnoreButtonUpWaitForFocusLoss = true;
+#endif
+
     // GLFW 3.2 unfortunately always set focus on glfwCreateWindow() if GLFW_VISIBLE is set, regardless of GLFW_FOCUSED
     // With GLFW 3.3, the hint GLFW_FOCUS_ON_SHOW fixes this problem
     glfwWindowHint(GLFW_VISIBLE, false);

docs/CHANGELOG.txt

@@ -55,6 +55,9 @@ Other changes:
 
 Docking+Viewports Branch:
 
+- Backends: GLFW: added Linux workaround for spurious mouse up events emitted while dragging
+  and creating new viewports. Generally they would be interrupting a dragging operations. 
+  (#3158, #7733, #7922) [@rokups, @ocornut]
 - Docking: fixed using ImGuiDockNodeFlags_KeepAliveOnly with DockSpaceOverViewport():
   the normally invisible space did erroneously claim mouse hover and could be potentially
   focused. (#8125) [@kcbanner]