CairoLineCap for details about how the available line cap
styles are drawn.cairoSetLineCap(cr, line.cap)crCairo] a cairo contextline.capCairoLineCap] a line cap stylecairoStroke, cairoStrokeExtents, and
cairoStrokeToPath(), but does not have any effect during path
construction.
The default line cap style is CAIRO_LINE_CAP_BUTT.