Fix MDI child windows not appearing and menu corruption for Win16 apps

src/components/EmulatorView.tsx

@@ -1187,11 +1187,14 @@ export function EmulatorView({ arrayBuffer, peInfo, additionalFiles, exeName, co
     const savedEIP = emu.cpu.eip;
     const savedWaiting = emu.waitingForMessage;
     emu.waitingForMessage = false;
-    emu.callWndProc(wnd.wndProc, emu.mainWindow, WM_INITMENU, hMenu, 0);
+    const callWndProc = emu.isNE
+      ? (wp: number, hw: number, m: number, w: number, l: number) => emu.callWndProc16(wp, hw, m, w, l)
+      : (wp: number, hw: number, m: number, w: number, l: number) => emu.callWndProc(wp, hw, m, w, l);
+    callWndProc(wnd.wndProc, emu.mainWindow, WM_INITMENU, hMenu, 0);
     // Get submenu handle for INITMENUPOPUP
     const menuData = hMenu ? emu.handles.get<{ items: { hSubMenu: number }[] }>(hMenu) : null;
     const hSubMenu = menuData?.items?.[index]?.hSubMenu || 0;
-    emu.callWndProc(wnd.wndProc, emu.mainWindow, WM_INITMENUPOPUP, hSubMenu, index);
+    callWndProc(wnd.wndProc, emu.mainWindow, WM_INITMENUPOPUP, hSubMenu, index);
     emu.cpu.reg[4] = savedESP;
     emu.cpu.eip = savedEIP;
     emu.waitingForMessage = savedWaiting;

src/lib/emu/win16/user/message.ts

@@ -1134,7 +1134,13 @@ export function registerWin16UserMessage(emu: Emulator, user: Win16Module, h: Wi
         const mdiTitle = titleAddr ? emu.memory.readCString(titleAddr) : '';
 
         const classInfo = emu.windowClasses.get(mdiClassName.toUpperCase());
-        console.log(`[WIN16] WM_MDICREATE class="${mdiClassName}" title="${mdiTitle}" ${mdiCX}x${mdiCY} style=0x${mdiStyle.toString(16)} wndProc=0x${(classInfo?.wndProc||0).toString(16)} cbExtra=${classInfo?.cbWndExtra||0} lParam=0x${mdiLParam.toString(16)}`);
+        // Sign-extend 16-bit coordinates (same as MoveWindow/SetWindowPos)
+        const CW_USEDEFAULT = -32768; // 0x8000 sign-extended
+        const mdiXs = (mdiX << 16) >> 16;
+        const mdiYs = (mdiY << 16) >> 16;
+        const mdiCXs = (mdiCX << 16) >> 16;
+        const mdiCYs = (mdiCY << 16) >> 16;
+        console.log(`[WIN16] WM_MDICREATE class="${mdiClassName}" title="${mdiTitle}" ${mdiCXs}x${mdiCYs} style=0x${mdiStyle.toString(16)} wndProc=0x${(classInfo?.wndProc||0).toString(16)} cbExtra=${classInfo?.cbWndExtra||0} lParam=0x${mdiLParam.toString(16)}`);
 
         const WS_CHILD = 0x40000000;
         const WS_VISIBLE = 0x10000000;
@@ -1152,15 +1158,24 @@ export function registerWin16UserMessage(emu: Emulator, user: Win16Module, h: Wi
         const { cw: mdiCW, ch: mdiCH } = getClientSize(wnd.style, false, wnd.width, wnd.height, true);
         const clientW = mdiCW || (emu.canvas?.width ?? 320);
         const clientH = mdiCH || (emu.canvas?.height ?? 200);
+        // Resolve position and size: CW_USEDEFAULT or negative → fill MDICLIENT area;
+        // if requested size exceeds client area, fill it entirely (Windows 3.1 behavior)
+        let childX = (mdiXs === CW_USEDEFAULT || mdiXs < 0) ? 0 : mdiXs;
+        let childY = (mdiYs === CW_USEDEFAULT || mdiYs < 0) ? 0 : mdiYs;
+        let childW = (mdiCXs === CW_USEDEFAULT || mdiCXs <= 0) ? clientW : mdiCXs;
+        let childH = (mdiCYs === CW_USEDEFAULT || mdiCYs <= 0) ? clientH : mdiCYs;
+        if (childW > clientW || childH > clientH) {
+          childX = 0; childY = 0; childW = clientW; childH = clientH;
+        }
         const childHwnd = emu.handles.alloc('window', {
           classInfo: classInfo || { className: mdiClassName, wndProc: 0, rawWndProc: 0, style: 0, hbrBackground: 0, hIcon: 0, hCursor: 0, cbWndExtra: 0 },
           title: mdiTitle,
           style: childStyle,
           exStyle: 0,
-          x: mdiX === 0x8000 ? 0 : mdiX,
-          y: mdiY === 0x8000 ? 0 : mdiY,
-          width: (mdiCX === 0x8000 || mdiCX === 0) ? clientW : mdiCX,
-          height: (mdiCY === 0x8000 || mdiCY === 0) ? clientH : mdiCY,
+          x: childX,
+          y: childY,
+          width: childW,
+          height: childH,
           hMenu: 0,
           parent: hWnd,
           wndProc: classInfo?.wndProc || 0,

src/lib/emu/win16/user/window.ts

@@ -624,7 +624,6 @@ export function registerWin16UserWindow(emu: Emulator, user: Win16Module, h: Win
     const [hWnd, _hInsertAfter, x, y, cx, cy, uFlags] = emu.readPascalArgs16([2, 2, 2, 2, 2, 2, 2]);
     const wnd = emu.handles.get<WindowInfo>(hWnd);
     if (!wnd) return 0;
-
     const SWP_NOSIZE = 0x1, SWP_NOMOVE = 0x2;
     const SWP_SHOWWINDOW = 0x40, SWP_HIDEWINDOW = 0x80;
     let sizeChanged = false;