From ea74c3c872c9fb80bd50b73661cafb8f2a262637 Mon Sep 17 00:00:00 2001
From: Sebastian <sebastian.e.gross@gmail.com>
Date: Sun, 20 Sep 2020 23:31:45 +0100
Subject: [PATCH] Fixed Linux crash caused by wrong mapping of key codes.

---
 CHANGES.md                                    |  1 +
 .../ImGui/Private/ImGuiInteroperability.cpp   | 29 +++++++++++++------
 Source/ImGui/Private/ImGuiInteroperability.h  |  5 +---
 3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index c130fff..3b70610 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -11,6 +11,7 @@ Improving stability
 - Improved hot-reload stability and support for reloading after recompiling outside of the editor. Both methods should be equally supported and work together.
 - Improved behaviour of delegates when hot-reloading.
 - Changed context index mapping to fix issues with multi-PIE debugging in 4.25.
+- Fixed Linux crash caused by wrong mapping of key codes.
 
 Version: 1.20 (2020/06)
 Transition to IWYU and maintenance:
diff --git a/Source/ImGui/Private/ImGuiInteroperability.cpp b/Source/ImGui/Private/ImGuiInteroperability.cpp
index aef13ec..e30247c 100644
--- a/Source/ImGui/Private/ImGuiInteroperability.cpp
+++ b/Source/ImGui/Private/ImGuiInteroperability.cpp
@@ -122,6 +122,17 @@ namespace ImGuiInterops
 		Copy(Mapping.KeyMap, IO.KeyMap);
 	}
 
+	// Simple transform mapping key codes to 0-511 range used in ImGui.
+	// From what I can tell, on most supported platforms key codes should comfortably fit in that range anyway
+	// but the SDL key-codes used on Linux can go way out of this range (because of the extra flag). However,
+	// after this transform they should fit in the range without conflicts.
+	// NOTE: Should any of the platforms have other conflicts or any trouble with inputs, this is the likely
+	// candidate for change.
+	static uint32 MapKeyCode(uint32 KeyCode)
+	{
+		return (KeyCode < 512) ? KeyCode : 256 + (KeyCode % 256);
+	}
+
 	uint32 GetKeyIndex(const FKey& Key)
 	{
 		const uint32* pKeyCode = nullptr;
@@ -129,17 +140,17 @@ namespace ImGuiInterops
 
 		FInputKeyManager::Get().GetCodesFromKey(Key, pKeyCode, pCharCode);
 
-		if (pKeyCode)
-		{
-			return *pKeyCode;
-		}
+		const uint32 KeyCode =
+			pKeyCode ? *pKeyCode
+			: pCharCode ? *pCharCode
+			: 0;
 
-		if (pCharCode)
-		{
-			return *pCharCode;
-		}
+		return MapKeyCode(KeyCode);
+	}
 
-		return 0;
+	uint32 GetKeyIndex(const FKeyEvent& KeyEvent)
+	{
+		return MapKeyCode(KeyEvent.GetKeyCode());
 	}
 
 	uint32 GetMouseIndex(const FKey& MouseButton)
diff --git a/Source/ImGui/Private/ImGuiInteroperability.h b/Source/ImGui/Private/ImGuiInteroperability.h
index 67918ae..62e4cd1 100644
--- a/Source/ImGui/Private/ImGuiInteroperability.h
+++ b/Source/ImGui/Private/ImGuiInteroperability.h
@@ -40,10 +40,7 @@ namespace ImGuiInterops
 	uint32 GetKeyIndex(const FKey& Key);
 
 	// Map key event to index in keys buffer.
-	FORCEINLINE uint32 GetKeyIndex(const FKeyEvent& KeyEvent)
-	{
-		return KeyEvent.GetKeyCode();
-	}
+	uint32 GetKeyIndex(const FKeyEvent& KeyEvent);
 
 	// Map mouse FKey to index in mouse buttons buffer.
 	uint32 GetMouseIndex(const FKey& MouseButton);