center MessageBox to the window of the program

src/Dialogs.c

@@ -102,9 +102,10 @@ int MsgBox(int iType,UINT uIdMsg,...)
     case MBOKCANCEL: iIcon = MB_ICONEXCLAMATION | MB_OKCANCEL; break;
   }
 
-  if (!(hwnd = GetFocus()))
+  if (!(hwnd = GetActiveWindow()))
     hwnd = hwndMain;
 
+  PostMessage(hwndMain, APPM_CENTER_MESSAGE_BOX, (WPARAM)hwnd, 0);
   return MessageBoxEx(hwnd,
            szText,szTitle,
            MB_SETFOREGROUND | iIcon,
@@ -138,6 +139,9 @@ void DisplayCmdLineHelp(HWND hwnd)
   mbp.lpfnMsgBoxCallback = NULL;
   mbp.dwLanguageId = MAKELANGID(LANG_NEUTRAL,SUBLANG_NEUTRAL);
 
+  if (hwnd != NULL) {
+    PostMessage(hwndMain, APPM_CENTER_MESSAGE_BOX, (WPARAM)hwnd, 0);
+  }
   MessageBoxIndirect(&mbp);
 }
 

src/Dialogs.h

@@ -26,6 +26,12 @@
 #define MBYESNOCANCEL  4
 #define MBOKCANCEL     8
 
+/**
+ * App message used to center MessageBox to the window of the program.
+ * https://stackoverflow.com/questions/6299797/c-how-to-center-messagebox
+ */
+#define APPM_CENTER_MESSAGE_BOX		(WM_APP + 1)
+
 int  MsgBox(int,UINT,...);
 void DisplayCmdLineHelp(HWND hwnd);
 BOOL GetDirectory(HWND,int,LPWSTR,LPCWSTR,BOOL);

src/Helpers.c

@@ -474,18 +474,19 @@ void SetWindowTransparentMode(HWND hwnd,BOOL bTransparentMode)
 //
 void CenterDlgInParent(HWND hDlg)
 {
+	CenterDlgInParentEx(hDlg, GetParent(hDlg));
+}
 
+void CenterDlgInParentEx(HWND hDlg, HWND hParent)
+{
   RECT rcDlg;
-  HWND hParent;
   RECT rcParent;
   MONITORINFO mi;
   HMONITOR hMonitor;
 
   int xMin, yMin, xMax, yMax, x, y;
 
   GetWindowRect(hDlg,&rcDlg);
-
-  hParent = GetParent(hDlg);
   GetWindowRect(hParent,&rcParent);
 
   hMonitor = MonitorFromRect(&rcParent,MONITOR_DEFAULTTONEAREST);
@@ -512,6 +513,30 @@ void CenterDlgInParent(HWND hDlg)
 
 }
 
+// Why doesn’t the "Automatically move pointer to the default button in a dialog box"
+// work for nonstandard dialog boxes, and how do I add it to my own nonstandard dialog boxes?
+// https://blogs.msdn.microsoft.com/oldnewthing/20130826-00/?p=3413/
+void SnapToDefaultButton(HWND hwndBox) {
+    BOOL fSnapToDefButton = FALSE;
+    if (SystemParametersInfo(SPI_GETSNAPTODEFBUTTON, 0, &fSnapToDefButton, 0) && fSnapToDefButton) {
+        // get child window at the top of the Z order.
+        // for all our MessageBoxs it's the OK or YES button or NULL.
+        HWND btn = GetWindow(hwndBox, GW_CHILD);
+        if (btn != NULL) {
+            WCHAR className[8] = L"";
+            GetClassName(btn, className, COUNTOF(className));
+            if (lstrcmpi(className, L"Button") == 0) {
+                RECT rect;
+                int x, y;
+                GetWindowRect(btn, &rect);
+                x = rect.left + (rect.right - rect.left) / 2;
+                y = rect.top + (rect.bottom - rect.top) / 2;
+                SetCursorPos(x, y);
+            }
+        }
+    }
+}
+
 
 //=============================================================================
 //

src/Helpers.h

@@ -89,7 +89,9 @@ BOOL SetWindowTitle(HWND,UINT,BOOL,UINT,LPCWSTR,int,BOOL,UINT,BOOL,LPCWSTR);
 void SetWindowTransparentMode(HWND,BOOL);
 
 
+void CenterDlgInParentEx(HWND hDlg, HWND hParent);
 void CenterDlgInParent(HWND);
+void SnapToDefaultButton(HWND hwndBox);
 void GetDlgPos(HWND,LPINT,LPINT);
 void SetDlgPos(HWND,int,int);
 void ResizeDlg_Init(HWND,int,int,int);

src/Notepad2.c

@@ -1520,6 +1520,16 @@ LRESULT CALLBACK MainWndProc(HWND hwnd,UINT umsg,WPARAM wParam,LPARAM lParam)
       }
       break;
 
+    case APPM_CENTER_MESSAGE_BOX: {
+        HWND box = FindWindow(L"#32770", NULL);
+        HWND parent = GetParent(box);
+        // MessageBox belongs to us.
+        if (parent == (HWND)wParam || parent == hwndMain) {
+            CenterDlgInParentEx(box, parent);
+            SnapToDefaultButton(box);
+        }
+      }
+      break;
 
     default: