getTrackbarPos function
Implementation
int getTrackbarPos(String trackbarName, String winName) {
final cTrackName = trackbarName.toNativeUtf8().cast<ffi.Char>();
final cwinname = winName.toNativeUtf8().cast<ffi.Char>();
final p = calloc<ffi.Int>();
cvRun(() => chighgui.cv_getTrackbarPos(cTrackName, cwinname, p));
final rval = p.value;
calloc.free(p);
calloc.free(cTrackName);
calloc.free(cwinname);
return rval;
}