Window input focus is based on WM_SETFOCUS and WM_KILLFOCUS as WM_ACTIVATE doesn't necessarily imply focus.

Hopefully resolves https://github.com/libsdl-org/SDL/issues/4450 and https://github.com/libsdl-org/SDL/pull/4293

src/video/windows/SDL_windowsevents.c

@@ -663,15 +663,10 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 
     case WM_ACTIVATE:
         {
-            POINT cursorPos;
             BOOL minimized;
 
             minimized = HIWORD(wParam);
             if (!minimized && (LOWORD(wParam) != WA_INACTIVE)) {
-                /* Don't mark the window as shown if it's activated before being shown */
-                if (!IsWindowVisible(hwnd)) {
-                    break;
-                }
                 if (LOWORD(wParam) == WA_CLICKACTIVE) {
                     SDL_bool swapButtons = GetSystemMetrics(SM_SWAPBUTTON) != 0;
                     if (GetAsyncKeyState(VK_LBUTTON)) {
@@ -692,42 +687,55 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                 }
 
                 SDL_SendWindowEvent(data->window, SDL_WINDOWEVENT_SHOWN, 0, 0);
-                if (SDL_GetKeyboardFocus() != data->window) {
-                    SDL_SetKeyboardFocus(data->window);
-                }
+            }
+        }
+        returnCode = 0;
+        break;
 
-                GetCursorPos(&cursorPos);
-                ScreenToClient(hwnd, &cursorPos);
-                SDL_SendMouseMotion(data->window, 0, 0, cursorPos.x, cursorPos.y);
+    case WM_SETFOCUS:
+        {
+            POINT cursorPos;
 
-                WIN_CheckAsyncMouseRelease(data);
-                WIN_UpdateClipCursor(data->window);
+            if (SDL_GetKeyboardFocus() != data->window) {
+                SDL_SetKeyboardFocus(data->window);
+            }
 
-                /*
-                 * FIXME: Update keyboard state
-                 */
-                WIN_CheckClipboardUpdate(data->videodata);
+            GetCursorPos(&cursorPos);
+            ScreenToClient(hwnd, &cursorPos);
+            SDL_SendMouseMotion(data->window, 0, 0, cursorPos.x, cursorPos.y);
 
-                SDL_ToggleModState(KMOD_CAPS, (GetKeyState(VK_CAPITAL) & 0x0001) != 0);
-                SDL_ToggleModState(KMOD_NUM, (GetKeyState(VK_NUMLOCK) & 0x0001) != 0);
-                SDL_ToggleModState(KMOD_SCROLL, (GetKeyState(VK_SCROLL) & 0x0001) != 0);
-            } else {
-                RECT rect;
+            WIN_CheckAsyncMouseRelease(data);
+            WIN_UpdateClipCursor(data->window);
 
-                data->in_window_deactivation = SDL_TRUE;
+            /*
+             * FIXME: Update keyboard state
+             */
+            WIN_CheckClipboardUpdate(data->videodata);
 
-                if (SDL_GetKeyboardFocus() == data->window) {
-                    SDL_SetKeyboardFocus(NULL);
-                    WIN_ResetDeadKeys();
-                }
+            SDL_ToggleModState(KMOD_CAPS, (GetKeyState(VK_CAPITAL) & 0x0001) != 0);
+            SDL_ToggleModState(KMOD_NUM, (GetKeyState(VK_NUMLOCK) & 0x0001) != 0);
+            SDL_ToggleModState(KMOD_SCROLL, (GetKeyState(VK_SCROLL) & 0x0001) != 0);
+        }
+        returnCode = 0;
+        break;
 
-                if (GetClipCursor(&rect) && SDL_memcmp(&rect, &data->cursor_clipped_rect, sizeof(rect)) == 0) {
-                    ClipCursor(NULL);
-                    SDL_zero(data->cursor_clipped_rect);
-                }
+    case WM_KILLFOCUS:
+        {
+            RECT rect;
+
+            data->in_window_deactivation = SDL_TRUE;
 
-                data->in_window_deactivation = SDL_FALSE;
+            if (SDL_GetKeyboardFocus() == data->window) {
+                SDL_SetKeyboardFocus(NULL);
+                WIN_ResetDeadKeys();
             }
+
+            if (GetClipCursor(&rect) && SDL_memcmp(&rect, &data->cursor_clipped_rect, sizeof(rect)) == 0) {
+                ClipCursor(NULL);
+                SDL_zero(data->cursor_clipped_rect);
+            }
+
+            data->in_window_deactivation = SDL_FALSE;
         }
         returnCode = 0;
         break;

src/video/windows/SDL_windowswindow.c

@@ -281,15 +281,8 @@ SetupWindowData(_THIS, SDL_Window * window, HWND hwnd, HWND parent, SDL_bool cre
     }
     if (GetFocus() == hwnd) {
         window->flags |= SDL_WINDOW_INPUT_FOCUS;
-        SDL_SetKeyboardFocus(data->window);
-
-        if (window->flags & SDL_WINDOW_MOUSE_GRABBED) {
-            RECT rect;
-            GetClientRect(hwnd, &rect);
-            ClientToScreen(hwnd, (LPPOINT) & rect);
-            ClientToScreen(hwnd, (LPPOINT) & rect + 1);
-            ClipCursor(&rect);
-        }
+        SDL_SetKeyboardFocus(window);
+        WIN_UpdateClipCursor(window);
     }
 
     /* Enable multi-touch */