# Regular polygons and ellipses in grid graphics

#### Baptiste Auguie

#### 2017-09-09

The `gridExtra` package provides a basic implementation of regular polygons, `ngonGrob()/grid.ngon`, and a convenience function to draw ellipses, `ellipseGrob()/grid.ellipse()`. We illustrate below the basic usage of these vectorised functions.

## Basic usage

    library(gridExtra)
    library(grid)
    library(grid)
    N <- 5
    xy <- polygon_regular(N)*2

    # draw multiple polygons
    g <- ngonGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
                  unit(xy[,2],"cm") + unit(0.5,"npc"),
                  n=seq_len(N)+2, gp=gpar(fill=1:N))

    grid.newpage()
    grid.draw(g)

## Rotated and stretched polygons

    g2 <- ngonGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
                  unit(xy[,2],"cm") + unit(0.5,"npc"),
                  n=seq_len(N)+2, ar=seq_len(N),
                  phase=0, angle=pi/(seq_len(N)+2),
                  size=1:N+5, gp=gpar(fill=1:N))

    grid.newpage()
    grid.draw(g2)

## Ellipses

    g3 <- ellipseGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
                      unit(xy[,2],"cm") + unit(0.5,"npc"),
                      angle=-2*seq(0,N-1)*pi/N+pi/2,
                      size=5, ar=3, gp=gpar(fill=1:N))

    grid.newpage()
    grid.draw(g3)