From 896f0a2fdd7e11a032a462ae585c79a86791e92c Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <icculus@icculus.org>
Date: Mon, 6 Jan 2025 11:29:38 -0500
Subject: [PATCH] windows: handle WM_POINTERCAPTURECHANGED events, fix
 maybe-undefined behavior.

Fixes #11843.
Fixes #11844.
---
 src/video/windows/SDL_windowsevents.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/video/windows/SDL_windowsevents.c b/src/video/windows/SDL_windowsevents.c
index 54609d03da9ad..b5e39f8a78439 100644
--- a/src/video/windows/SDL_windowsevents.c
+++ b/src/video/windows/SDL_windowsevents.c
@@ -94,6 +94,9 @@
 #ifndef WM_POINTERLEAVE
 #define WM_POINTERLEAVE 0x024A
 #endif
+#ifndef WM_POINTERCAPTURECHANGED
+#define WM_POINTERCAPTURECHANGED 0x024C
+#endif
 #ifndef WM_UNICHAR
 #define WM_UNICHAR 0x0109
 #endif
@@ -1163,18 +1166,17 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
         returnCode = 0;
     } break;
 
+    case WM_POINTERCAPTURECHANGED:
     case WM_POINTERLEAVE:
     {
         const UINT32 pointerid = GET_POINTERID_WPARAM(wParam);
         void *hpointer = (void *) (size_t) pointerid;
         const SDL_PenID pen = SDL_FindPenByHandle(hpointer);
-        if (pen == 0) {
-            break;  // not a pen, or not a pen we already knew about.
-        }
-
-        // if this just left the _window_, we don't care. If this is no longer visible to the tablet, time to remove it!
-        if (!IS_POINTER_INCONTACT_WPARAM(wParam)) {
-            SDL_RemovePenDevice(WIN_GetEventTimestamp(), pen);
+        if (pen != 0) {
+            // if this just left the _window_, we don't care. If this is no longer visible to the tablet, time to remove it!
+            if ((msg == WM_POINTERCAPTURECHANGED) || !IS_POINTER_INCONTACT_WPARAM(wParam)) {
+                SDL_RemovePenDevice(WIN_GetEventTimestamp(), pen);
+            }
         }
         returnCode = 0;
     } break;
@@ -1182,6 +1184,7 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
     case WM_POINTERUPDATE: {
         POINTER_INPUT_TYPE pointer_type = PT_POINTER;
         if (!data->videodata->GetPointerType || !data->videodata->GetPointerType(GET_POINTERID_WPARAM(wParam), &pointer_type)) {
+            returnCode = 0;
             break;  // oh well.
         }
 
@@ -1195,6 +1198,8 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
 
     case WM_POINTERDOWN:
     case WM_POINTERUP: {
+        returnCode = 0;  // always mark this event handled, so it doesn't go to DefWindowProc (see #11843).
+
         POINTER_PEN_INFO pen_info;
         const UINT32 pointerid = GET_POINTERID_WPARAM(wParam);
         void *hpointer = (void *) (size_t) pointerid;
@@ -1242,8 +1247,6 @@ LRESULT CALLBACK WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lPara
         if (msg == WM_POINTERDOWN) {
             SDL_SendPenTouch(timestamp, pen, window, (pen_info.penFlags & PEN_FLAG_INVERTED) != 0, true);
         }
-
-        returnCode = 0;
     } break;
 
     case WM_MOUSEMOVE: