IO: modify io.AddFocusEvent() to tolerate in/out for multi-viewports.…

… Amend 2f40be6. (merged from docking) (#3532)

imgui.cpp

@@ -1185,13 +1185,8 @@ void ImGuiIO::ClearInputCharacters()
     InputQueueCharacters.resize(0);
 }
 
-void ImGuiIO::AddFocusEvent(bool focused)
+void ImGuiIO::ClearInputKeys()
 {
-    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;
@@ -1201,6 +1196,13 @@ void ImGuiIO::AddFocusEvent(bool focused)
         NavInputsDownDuration[n] = NavInputsDownDurationPrev[n] = -1.0f;
 }
 
+void ImGuiIO::AddFocusEvent(bool focused)
+{
+    // We intentionally overwrite this and process in NewFrame(), in order to give a chance
+    // to multi-viewports backends to queue AddFocusEvent(false),AddFocusEvent(true) in same frame.
+    AppFocusLost = !focused;
+}
+
 //-----------------------------------------------------------------------------
 // [SECTION] MISC HELPERS/UTILITIES (Geometry functions)
 //-----------------------------------------------------------------------------
@@ -4070,6 +4072,14 @@ void ImGui::NewFrame()
     g.DragDropWithinTarget = false;
     g.DragDropHoldJustPressedId = 0;
 
+    // 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)
+    if (g.IO.AppFocusLost)
+    {
+        g.IO.ClearInputKeys();
+        g.IO.AppFocusLost = false;
+    }
+
     // Update keyboard input state
     // Synchronize io.KeyMods with individual modifiers io.KeyXXX bools
     g.IO.KeyMods = GetMergedKeyModFlags();

imgui.h

@@ -1892,8 +1892,9 @@ struct ImGuiIO
     IMGUI_API void  AddInputCharacter(unsigned int c);          // Queue new character input
     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
+    IMGUI_API void  ClearInputCharacters();                     // [Internal] Clear the text input buffer manually
+    IMGUI_API void  ClearInputKeys();                           // [Internal] Release all keys
 
     //------------------------------------------------------------------
     // Output - Updated by NewFrame() or EndFrame()/Render()
@@ -1941,6 +1942,7 @@ struct ImGuiIO
     float       NavInputsDownDuration[ImGuiNavInput_COUNT];
     float       NavInputsDownDurationPrev[ImGuiNavInput_COUNT];
     float       PenPressure;                    // Touch/Pen pressure (0.0f to 1.0f, should be >0.0f only when MouseDown[0] == true). Helper storage currently unused by Dear ImGui.
+    bool        AppFocusLost;
     ImWchar16   InputQueueSurrogate;            // For AddInputCharacterUTF16
     ImVector<ImWchar> InputQueueCharacters;     // Queue of _characters_ input (obtained by platform backend). Fill using AddInputCharacter() helper.