setTrackbarPos function
Implementation
void setTrackbarPos(String trackbarName, String winName, int pos) {
final cTrackName = trackbarName.toNativeUtf8().cast<ffi.Char>();
final cwinname = winName.toNativeUtf8().cast<ffi.Char>();
cvRun(() => chighgui.cv_setTrackbarPos(cTrackName, cwinname, pos));
calloc.free(cTrackName);
calloc.free(cwinname);
}