Õîðîøèé âèäîñèê ïîïàëñÿ ïî òåìå https://www.youtube.com/watch?v=ETq8Ja7UTSc
Ãðóáîâàòàÿ ðàáîòà, íî ... êàê ìèíèìóì âñ¸ ïîíÿòíî.