function GetHeadingDiff(_Heading1, _Heading2)
{   
    return (_Heading2-_Heading1+540) % 360 - 180;
}

示例:

GetHeadingDiff( 280, 270 )
-10
GetHeadingDiff( 270, 280 )
10
GetHeadingDiff( 350, 20 )
30
GetHeadingDiff( 20, 350 )
-30