R code to generate a random christmas tree

xmas-tree.R

# This appeared on R-blogger, a post by "wingfeet" from 23 December 2013: http://www.r-bloggers.com/merry-christmas-2/
# I stumbled acroos it and didn't want to lose it so I placed it here
part <- list(x0=0,y0=0,x1=0,y1=1,
             branch1=NULL,branch2=NULL,extend=NULL,
             lwd=1,depth=0,col='springgreen')

par(mfrow=c(1,1),mar=c(5, 4, 4, 2) + 0.1)
segplot <- function(tree) {
  if (is.null(tree)) return()
  segments(tree$x0,tree$y0,tree$x1,tree$y1,
           col=tree$col,
           lwd=tree$lwd)
  segplot(tree$branch1)
  segplot(tree$branch2)
  segplot(tree$extend)
}
#segplot(part)

grow <- function(tree) {
  if (is.null(tree) ) return(NULL)
  
  tree$lwd=tree$lwd*1.2
  
  if (tree$lwd>2.5) tree$col <- 'brown'
  if (is.null(tree$extend)) {
    tree$extend <- list(
      x0=tree$x1,
      y0=tree$y1,
      x1=rnorm(1,1,.03)*(2*tree$x1-tree$x0),
      y1=(rnorm(1,.98,.02)+.02*(tree$x1==tree$x0))*(2*tree$y1-tree$y0),
      branch1=NULL,
      branch2=NULL,
      extend=NULL,
      lwd=1,
      depth=tree$depth,
      col=tree$col
    )
    length=sqrt((tree$x1-tree$x0)^2 + (tree$y1-tree$y0)^2)
    angle <- asin((tree$x1-tree$x0)/length)
    branch <- list(
      x0=(tree$x1+tree$x0)/2,
      y0=(tree$y1+tree$y0)/2,
      branch1=NULL,
      branch2=NULL,
      extend=NULL,
      lwd=1,
      depth=tree$depth,
      col=tree$col
    )
    shift <- rnorm(2,.5,.1)
    branch$x0 <- shift[1]*tree$x1+(1-shift[1])*tree$x0
    branch$y0 <- shift[1]*tree$y1+(1-shift[1])*tree$y0
    length=length*rnorm(1,.5,.05)
    co <- runif(1,.35,.45)
    branch$x1 <- branch$x0+sin(angle+co)*length
    branch$y1 <- branch$y0+cos(angle+co)*length
    tree$branch1 <- branch
    branch$x0 <- shift[2]*tree$x1+(1-shift[2])*tree$x0
    branch$y0 <- shift[2]*tree$y1+(1-shift[2])*tree$y0
    co <- runif(1,.35,.45)
    branch$x1 <- branch$x0+sin(angle-co)*length
    branch$y1 <- branch$y0+cos(angle-co)*length
    tree$branch2 <- branch    
  } else {
    tree$branch1 <- grow(tree$branch1)
    tree$branch2 <- grow(tree$branch2)
    tree$extend <- grow(tree$extend)
  }
  tree$depth <- tree$depth+1
  if (tree$depth>2)  tree$col <- 'green'
  if (tree$depth>4)  tree$col <- 'darkgreen'
  if (tree$depth>6)  tree$col <- 'brown'
  
  tree
}
tree <- part
for (i in 1:9) tree <- grow(tree) 
par(mar=c(0,0,0,0))
plot(x=c(-3,3),y=c(0,9),type='n',axes=FALSE,xlab='',ylab='')
segplot(tree)