Changes have been done, thank you!
and here is a new one to avoid moving unexpectedly the slider button while using the threshold gauge.
y = 422;
hCtrl = addLabel(gP.hMain, LAB_STRAYLIGHT, L"Straylight", ClientW - 129, y, 120, 13, WS_CHILD | WS_VISIBLE | SS_LEFT);
// ML 01-02-2018: scene brightness
y += 15;
dwStyle = WS_CHILD | WS_VISIBLE | TBS_HORZ | TBS_RIGHT;
hCtrl = CreateWindowExW(0, L"msctls_trackbar32", $NULL, dwStyle, ClientW - 127, y, 120, 16, gP.hMain, (HMENU)IDC_BRIGHT_CONTROL, gP.hInstance, NULL);
SendMessage(hCtrl, TBM_SETRANGE, TRUE, MAKELONG(0, 100)); // Both WinLIFT and GDImage support negative ranges, for example -50, 50; then 0 being the medium value
SendMessage(hCtrl, TBM_SETPOS, TRUE, 100);
y += 31;
hCtrl = CreateWindowEx(0, L"BUTTON", L"Alpha value", WS_CHILD | WS_VISIBLE | BS_AUTOCHECKBOX,
ClientW - 127, y, 88, 16, gP.hMain, (HMENU) IDC_GAUGE_CHECKBOX, gP.hInstance, NULL);