From 96839b445e32e46d87a44fd43a9cdd60c806f7e1 Mon Sep 17 00:00:00 2001
From: ocornut <omarcornut@gmail.com>
Date: Thu, 25 Jan 2024 15:43:19 +0100
Subject: [PATCH] Nav: Improve handling of Alt key to toggle menu so that key
 ownership may be claimed on indiviudal left/right alt key without intefering
 with the other.

See test "inputs_owner_single_mod"
---
 docs/CHANGELOG.txt |  2 ++
 imgui.cpp          | 27 ++++++++++++++++-----------
 imgui_internal.h   |  2 ++
 3 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 7278ddb79..5ec7a2edc 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -54,6 +54,8 @@ Other changes:
 - Nav: Fixed SetKeyboardFocusHere() not working when current nav focus is in different scope,
   regression from 1.90.1 related to code scoping Tab presses to local scope. (#7226) [@bratpilz]
 - Nav: Fixed pressing Escape while in a child window with _NavFlattened flag. (#7237)
+- Nav: Improve handling of Alt key to toggle menu so that key ownership may be claimed on
+  indiviudal left/right alt key without intefering with the other.
 - Debug Tools: Metrics: Fixed debug break in SetShortcutRouting() not handling ImGuiMod_Shortcut redirect.
 - Debug Tools: Debug Log: Added "Input Routing" logging.
 - Debug Tools: Added "nop" to IM_DEBUG_BREAK macro on GCC to work around GDB bug (#7266) [@Peter0x44]
diff --git a/imgui.cpp b/imgui.cpp
index 040e6712c..8bfc66cb2 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -12627,28 +12627,33 @@ static void ImGui::NavUpdateWindowing()
     }
 
     // Keyboard: Press and Release ALT to toggle menu layer
-    // - Testing that only Alt is tested prevents Alt+Shift or AltGR from toggling menu layer.
-    // - AltGR is normally Alt+Ctrl but we can't reliably detect it (not all backends/systems/layout emit it as Alt+Ctrl). But even on keyboards without AltGR we don't want Alt+Ctrl to open menu anyway.
-    if (nav_keyboard_active && IsKeyPressed(ImGuiMod_Alt, ImGuiKeyOwner_None))
-    {
-        g.NavWindowingToggleLayer = true;
-        g.NavInputSource = ImGuiInputSource_Keyboard;
-    }
+    const ImGuiKey windowing_toggle_keys[] = { ImGuiKey_LeftAlt, ImGuiKey_RightAlt };
+    for (ImGuiKey windowing_toggle_key : windowing_toggle_keys)
+        if (nav_keyboard_active && IsKeyPressed(windowing_toggle_key, ImGuiKeyOwner_None))
+        {
+            g.NavWindowingToggleLayer = true;
+            g.NavWindowingToggleKey = windowing_toggle_key;
+            g.NavInputSource = ImGuiInputSource_Keyboard;
+            break;
+        }
     if (g.NavWindowingToggleLayer && g.NavInputSource == ImGuiInputSource_Keyboard)
     {
         // We cancel toggling nav layer when any text has been typed (generally while holding Alt). (See #370)
         // We cancel toggling nav layer when other modifiers are pressed. (See #4439)
+        // - AltGR is Alt+Ctrl on some layout but we can't reliably detect it (not all backends/systems/layout emit it as Alt+Ctrl).
         // We cancel toggling nav layer if an owner has claimed the key.
-        if (io.InputQueueCharacters.Size > 0 || io.KeyCtrl || io.KeyShift || io.KeySuper || TestKeyOwner(ImGuiMod_Alt, ImGuiKeyOwner_None) == false)
+        if (io.InputQueueCharacters.Size > 0 || io.KeyCtrl || io.KeyShift || io.KeySuper)
+            g.NavWindowingToggleLayer = false;
+        if (TestKeyOwner(g.NavWindowingToggleKey, ImGuiKeyOwner_None) == false || TestKeyOwner(ImGuiMod_Alt, ImGuiKeyOwner_None) == false)
             g.NavWindowingToggleLayer = false;
 
-        // Apply layer toggle on release
+        // Apply layer toggle on Alt release
         // 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 (IsKeyReleased(ImGuiMod_Alt) && g.NavWindowingToggleLayer)
+        if (IsKeyReleased(g.NavWindowingToggleKey) && g.NavWindowingToggleLayer)
             if (g.ActiveId == 0 || g.ActiveIdAllowOverlap)
                 if (IsMousePosValid(&io.MousePos) == IsMousePosValid(&io.MousePosPrev))
                     apply_toggle_layer = true;
-        if (!IsKeyDown(ImGuiMod_Alt))
+        if (!IsKeyDown(g.NavWindowingToggleKey))
             g.NavWindowingToggleLayer = false;
     }
 
diff --git a/imgui_internal.h b/imgui_internal.h
index f26ebceaf..925070629 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -2078,6 +2078,7 @@ struct ImGuiContext
     float                   NavWindowingTimer;
     float                   NavWindowingHighlightAlpha;
     bool                    NavWindowingToggleLayer;
+    ImGuiKey                NavWindowingToggleKey;
     ImVec2                  NavWindowingAccumDeltaPos;
     ImVec2                  NavWindowingAccumDeltaSize;
 
@@ -2329,6 +2330,7 @@ struct ImGuiContext
         NavWindowingTarget = NavWindowingTargetAnim = NavWindowingListWindow = NULL;
         NavWindowingTimer = NavWindowingHighlightAlpha = 0.0f;
         NavWindowingToggleLayer = false;
+        NavWindowingToggleKey = ImGuiKey_None;
 
         DimBgRatio = 0.0f;