Adding child window to Metatrader4's chart via DLL - blinking (not redrawing) - c++

Question

I would like to add a child window to Metatrader4's chart window which always stays on top, without blinking, just statically there all the time upon eveything (in parent window). I am doing this from a DLL (C++).
I call this method from the mql side:
MT4_EXPFUNC int __stdcall testWindow(HWND hwnd) {
prnt_hWnd = hwnd;
CreateThread(0, NULL, ThreadProc, (LPVOID)L"Window Title", NULL, NULL);
return 0;
}
The parent window's (chart) handle is given as a parameter.
DWORD WINAPI ThreadProc( LPVOID lpParam )
{
MSG messages;
/*
... in createWindowClass:
WNDCLASSEX wc;
wc.hInstance = GetModuleHandle(NULL);
wc.lpszClassName = (LPCWSTR)L"MyClass";
wc.lpszClassName = (LPCWSTR)szClassName;
wc.lpfnWndProc = DLLWindowProc;
wc.style = CS_HREDRAW | CS_VREDRAW | CS_DBLCLKS;
...
*/
CreateWindowClass(L"MyClass");
HWND hwnd = CreateWindowEx (0, L"MyClass", NULL, WS_VISIBLE | WS_CHILD , CW_USEDEFAULT, CW_USEDEFAULT, 400, 300, prnt_hWnd, NULL, GetModuleHandle(NULL), NULL );
ShowWindow (hwnd, SW_SHOWNORMAL);
while (GetMessage (&messages, NULL, 0, 0))
{
TranslateMessage(&messages);
DispatchMessage(&messages);
}
return 1;
}
I handle window's messages this way:
LRESULT CALLBACK DLLWindowProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message) {
case WM_PAINT: {
PAINTSTRUCT ps;
BeginPaint( hwnd, &ps );
EndPaint( hwnd, &ps );
return 0;
}
case WM_COMMAND:
/* */
break;
case WM_DESTROY:
PostQuitMessage (0);
break;
default:
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}
My child window at the begining appears, then after (I guess) the parent window is getting being redrawn, suddenly it disappears, then it is just blinking (fastly appears-disappear).
My goal is to have a child window on that chart statically, so always topmost, without blinking. I could achieve this only without the WS_CHILD property. But then my child window is not ON the parent.

Answer 1

Try adding the WS_CLIPCHILDREN style to the chart window. I would pass the handle on the MQL4 side in init() via some MT4 export function. For example, SetChartWnd( HWND hChartWnd ) and passing WindowHandle( Symbol(), Period() ) as the parameter.
Then inside that function, I would try doing something like the following:
if ( ::IsWindow( hChartWnd ) ) {
DWORD style = GetWindowLong( hChartWnd, GWL_STYLE );
style |= WS_CLIPCHILDREN;
SetWindowLong( hChartWnd, GWL_STYLE, style );
}
}