how to convert date from Gregorian(english) to islamic/Hijri

Actually openerp use dhtmlxscheduler calendar for calendar view in web_calendar module.But it provide Gregorian calendar.

Now the problem is that i would like to implement new calender view for Islamic calendar. And i also want to use dhtmlxscheduler. but it is not provide Islamic calendar support. i spend couple of hours to achieve dhtmlxscheduler Islamic or hijari calendar. but i can’t find usefully information.

Can any one help me how can i achieve dhtmlxscheduler Islamic or hijari calendar ?