ラインキャップスタイル（線の端のスタイル）を設定します。
type
TLineCapStyle = ( lcButtEnd, lcRoundEnd, lcProjectSquareEnd );
Delphi 構文:
procedure SetLineCap ( Linecap: TLineCapStyle );
C++ 構文:
void __fastcall SetLineCap ( TLineCapStyle Linecap );
説明:
グラフィックス状態のラインキャップスタイルを設定します。
Value Meaning
lcButtEnd Butt cap. The stroke is squared off at the endpoint of the path.
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. The stroke continues beyond the endpoint of the path
for a distance equal to half the line width and is then squared off. 