void cvSetPreprocessFuncWin32(CvWin32WindowCallback on_preprocess) {
    void *fptr;

    fptr = dlsym(_Chhighgui_handle, "cvSetPreprocessFuncWin32_chdl");
    if(fptr == NULL) {
        fprintf(_stderr, "Error: %s(): dlsym(): %s\n", __func__,  dlerror());
        return;
    }
    dlrunfun(fptr, NULL, cvSetPreprocessFuncWin32, on_preprocess);
}