drag drag sourc drag event drag sourc drag event transfer tf drag sourc drag event drag sourc context transfer mous locat screen point drag loc drag sourc drag event locat tree locat screen point tree loc locat screen substract locat tree drag loc translat tree loc tree loc tree path destin path path locat drag loc drag loc valid drag destin path tf drag sourc drag event drag sourc context set cursor drag sourc drop drag sourc drag event drag sourc context set cursor drag sourc copi drop 