追記 3-13

uhoplot の Window を開くところでの sleep 時間が短すぎたらしい。
CALL SLEEP(100) から CALL SLEEP(500) でとりあえずよし？

!----------------------------------------------------------------
SUBROUTINE gr_on(text, nx, ny)
USE IFMT ! multithread module
IMPLICIT NONE
CHARACTER (LEN = *), INTENT(IN), OPTIONAL :: text
INTEGER            , INTENT(IN), OPTIONAL :: nx, ny
INTEGER (BOOL)    :: iretb
INTEGER (HANDLE)  :: hBmp
INTEGER (LPDWORD) :: id
TYPE (T_RECT)    :: rc
IF (PRESENT(text)) wnd%title = TRIM(text)
IF (PRESENT(nx)  ) wnd%nsize_x = nx
IF (PRESENT(ny)  ) wnd%nsize_y = ny
CALL InitializeCriticalSection(LOC(lpCriticalSection))
wnd%hThread = CreateThread(0, 0, Thread_Proc, LOC(wnd), CREATE_SUSPENDED, id)
wnd%id      = id
iretb       = SetThreadPriority(wnd%hThread, THREAD_PRIORITY_BELOW_NORMAL)
iretb       = ResumeThread(wnd%hThread)
CALL Sleep(500) ! wait for Window initialization 
iretb = GetClientRect(wnd%hWnd, rc)
hBmp  = CreateCompatibleBitmap(wnd%hDC, rc%right - rc%left, rc%bottom - rc%top)
iretb = SelectObject(wnd%hDC, hBmp)
iretb = DeleteObject(hBmp)
iretb = PatBlt(wnd%hDC, 0, 0, rc%right - rc%left, rc%bottom - rc%top, WHITENESS)
wnd%hPen = CreatePen(PS_SOLID, 1, 0)
RETURN
END SUBROUTINE gr_on
!----------------------------------------------------------------

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なんか再帰にいいイメージが無いのはオカルトっぽいから？ｗ