x <- c(.3, .7, .3) y <- c(.2, .5, .8) grid.rect(gp=gpar(col="gray")) grid.lines(x, y, gp=gpar(lwd=40, lineend="square", linejoin="mitre", col="black")) grid.lines(x, y, gp=gpar(lwd=40, col="gray50")) # lineend="round", linejoin="round" grid.lines(x, y, gp=gpar(lwd=40, lineend="butt", linejoin="bevel", col="gray80")) grid.points(x, y, default.units="npc", pch=16, gp=gpar(cex=0.5))