設定 graphics state 中的 line cap style
type
lcButtEnd Butt cap。stroke 會在 path endpoint 處切成方形
Delphi 語法：
procedure SetLineCap ( Linecap: TLineCapStyle );
C++ 語法：
void __fastcall SetLineCap ( TLineCapStyle Linecap );
描述：
設定 graphics state 中的 line cap style
數值意義
lcButtEnd Butt cap。stroke 會在 path endpoint 處切成方形
There is no projection beyond the end of the path.
lcRoundEnd Round cap. A semicircular arc with a diameter equal to the line width
is drawn around the endpoint and filled in. 
lcProjectSquareEnd Projecting square cap。stroke 會延伸超過 path endpoint
延伸距離等於 line width 的一半，然後切成方形