gradient <- linearGradient(c("black", "white", "black"), 
                           x0=0, y0=.5, x1=1, y1=.5)


grid.rect(name="r1")
grid.gradientFill("r1", gradient)
cp <- clipPath(circleGrob())
grid.clipPath("r1", cp)


grid.rect(name="r2")
grid.gradientFill("r2", gradient)
cp <- clipPath(circleGrob(x=1:3/4, r=.3))
grid.clipPath("r2", cp)


pdf(NULL, width=12, height=3)
# grid.newpage()
pushViewport(viewport(x=1/4, width=.4, height=.8))
grid.rect(gp=gpar(col="grey"))
grid.rect(name="r1")
grid.gradientFill("r1", gradient)
cp <- clipPath(circleGrob())
grid.clipPath("r1", cp)
popViewport()
pushViewport(viewport(x=3/4, width=.4, height=.8))
grid.rect(gp=gpar(col="grey"))
grid.rect(name="r2")
grid.gradientFill("r2", gradient)
cp <- clipPath(circleGrob(x=1:3/4, r=.3))
grid.clipPath("r2", cp)
popViewport()
grid.export("Figures/export-clippath.svg")
dev.off()
system("chromium-browser --headless --screenshot=Figures/export-clippath.png --window-size=880x220 Figures/export-clippath.svg")
system("cp Figures/export-clippath.png Web/export-clippath.png")