[NTUSER] Implement NtUserCreateInputContext (#4230)

- Modify NtUserCreateInputContext prototype.
- Add UserCreateInputContext helper function.
- Implement NtUserCreateInputContext function by using UserCreateInputContext.
- Call UserCreateInputContext(0) in InitThreadCallback function to create the default input context.
CORE-11700

dll/win32/imm32/imm.c

@@ -597,7 +597,7 @@ HIMC WINAPI ImmCreateContext(void)
     if (pClientImc == NULL)
         return NULL;
 
-    hIMC = NtUserCreateInputContext(pClientImc);
+    hIMC = NtUserCreateInputContext((ULONG_PTR)pClientImc);
     if (hIMC == NULL)
     {
         Imm32HeapFree(pClientImc);

win32ss/include/ntuser.h

@@ -1937,7 +1937,7 @@ NtUserCreateDesktop(
 
 HIMC
 NTAPI
-NtUserCreateInputContext(PCLIENTIMC pClientImc);
+NtUserCreateInputContext(ULONG_PTR dwClientImcData);
 
 NTSTATUS
 NTAPI

win32ss/user/ntuser/main.c

@@ -651,6 +651,12 @@ InitThreadCallback(PETHREAD Thread)
     }
     ptiCurrent->pClientInfo->dwTIFlags = ptiCurrent->TIF_flags;
 
+    /* Create the default input context */
+    if (IS_IMM_MODE())
+    {
+        UserCreateInputContext(0);
+    }
+
     /* Last things to do only if we are not a SYSTEM or CSRSS thread */
     if (!(ptiCurrent->TIF_flags & (TIF_SYSTEMTHREAD | TIF_CSRSSTHREAD)))
     {

win32ss/user/ntuser/ntstubs.c

@@ -461,12 +461,63 @@ NtUserYieldTask(VOID)
    return 0;
 }
 
+PIMC FASTCALL UserCreateInputContext(ULONG_PTR dwClientImcData)
+{
+    PIMC pIMC;
+    PTHREADINFO pti = PsGetCurrentThreadWin32Thread();
+    PDESKTOP pdesk = pti->rpdesk;
+
+    if (!IS_IMM_MODE() || (pti->TIF_flags & TIF_DISABLEIME)) // Disabled?
+        return NULL;
+
+    if (!pdesk) // No desktop?
+        return NULL;
+
+    // pti->spDefaultImc should be already set if non-first time.
+    if (dwClientImcData && !pti->spDefaultImc)
+        return NULL;
+
+    // Create an input context user object.
+    pIMC = UserCreateObject(gHandleTable, pdesk, pti, NULL, TYPE_INPUTCONTEXT, sizeof(IMC));
+    if (!pIMC)
+        return NULL;
+
+    if (dwClientImcData) // Non-first time.
+    {
+        // Insert pIMC to the second position (non-default) of the list.
+        pIMC->pImcNext = pti->spDefaultImc->pImcNext;
+        pti->spDefaultImc->pImcNext = pIMC;
+    }
+    else // First time. It's the default IMC.
+    {
+        // Add the first one (default) to the list.
+        pti->spDefaultImc = pIMC;
+        pIMC->pImcNext = NULL;
+    }
+
+    pIMC->dwClientImcData = dwClientImcData; // Set it.
+    return pIMC;
+}
+
 HIMC
 APIENTRY
-NtUserCreateInputContext(PCLIENTIMC pClientImc)
+NtUserCreateInputContext(ULONG_PTR dwClientImcData)
 {
-    STUB;
+    PIMC pIMC;
-    return NULL;
+    HIMC ret = NULL;
+
+    UserEnterExclusive();
+
+    if (!IS_IMM_MODE() || !dwClientImcData)
+        goto Quit;
+
+    pIMC = UserCreateInputContext(dwClientImcData);
+    if (pIMC)
+        ret = UserHMGetHandle(pIMC);
+
+Quit:
+    UserLeave();
+    return ret;
 }
 
 DWORD

win32ss/user/ntuser/userfuncs.h

@@ -165,6 +165,7 @@ BOOL FASTCALL GetLayeredStatus(PWND pWnd);
 
 /************** INPUT CONTEXT **************/
 
+PIMC FASTCALL UserCreateInputContext(ULONG_PTR dwClientImcData);
 VOID UserFreeInputContext(PVOID Object);
 BOOLEAN UserDestroyInputContext(PVOID Object);
 PVOID AllocInputContextObject(PDESKTOP pDesk, PTHREADINFO pti, SIZE_T Size, PVOID* HandleOwner);