Christmas scene

The challenge

Time for something different! Can you create a seasonally-themed image?

It could be a winter scene or have a Christmas/Hanukkah theme. Use the concept of layers (e.g. ggplot2) to build an image. Can be static or animated. Can use AI tools (e.g. Claude/ChatGPT) to develop code using a series of prompts.

First, we have to create a perfect winter background.

Snowflakes

To start, we simulate a winter sky filled with snowflakes of various sizes.
The function below places N snowflakes randomly within a defined canvas, ensuring that no two snowflakes appear closer than a user-specified minimum distance d.

generate_snowflakes <- function(N, d, xmin = 0, xmax = 1, ymin = 0, ymax = 1) {
  pts <- data.frame(NA, nrow = N, ncol = 3)
  count <- 0
  i <- 0
  
  while (count < N && i < 5000) {
    i <- i + 1
    x <- runif(1, xmin, xmax)
    y <- runif(1, ymin, ymax)
    size <- round(runif(1, 3, 8))

    if (count == 0) {
      flag <- TRUE
      }
    
    if (count != 0)  {
      dists <- sqrt((pts[1:count, 1] - x)^2 + (pts[1:count, 2] - y)^2)
      flag <- all(dists >= d)
    }
    
    if (flag == TRUE) {
      count <- count + 1
      pts[count, ] <- c(x, y, size)
    }
  }
  
  colnames(pts) <- c("x", "y", "size")
  return(pts)
}

snowflakes <- generate_snowflakes(
  N = 300,
  d = 25,        
  xmin = 0, xmax = 450,
  ymin = 0, ymax = 450
)

Bright winter sky

Once the snowflake coordinates are generated, we place them onto a light blue background representing bright winter sky. Snowflakes are represented using the ’*’ (asterisk) character.

snowy_background <- ggplot(data = snowflakes) +
  annotate("rect", xmin = 0, xmax = 450, ymin = 0, ymax = 450, fill = "lightskyblue", alpha = 0.8) +
  geom_text(aes(x = x, y = y, label = '*'), color="white", size = snowflakes$size) +
  theme_classic() +
  theme(
    line = element_blank(),
    text = element_blank()
  )

snowy_background

Distant fur trees

To give the scene some depth, we add a row of distant fir trees.

fur_tree <- function(xstart, length, colour) {
  
  pts <- data.frame(NA)
  
  x_coord <- c(xstart, (2*xstart+length)/2, xstart+length)
  y_coord <- c(0, 2*sqrt(2)*length, 0)
  pts <- data.frame(x_coord, y_coord, colour)

  tree <- geom_polygon(data = pts, aes(x = x_coord, y = y_coord), fill = colour, alpha = 0.5)
  
  return(tree)
}

Now we can add fur trees to the snowy background:

snowy_background +
  fur_tree(xstart = 0, length = 50, colour = "palegreen4") +
  fur_tree(xstart = 20, length = 80, colour = "darkolivegreen") +
  fur_tree(xstart = 50, length = 75, colour = "palegreen4") +
  fur_tree(xstart = 100, length = 45, colour = "darkolivegreen") +
  fur_tree(xstart = 120, length = 50, colour = "darkolivegreen") +
  fur_tree(xstart = 150, length = 35, colour = "palegreen4") +
  fur_tree(xstart = 170, length = 55, colour = "darkolivegreen") +
  fur_tree(xstart = 200, length = 70, colour = "palegreen4") +
  fur_tree(xstart = 250, length = 45, colour = "darkolivegreen") +
  fur_tree(xstart = 280, length = 50, colour = "palegreen4") +
  fur_tree(xstart = 300, length = 35, colour = "darkolivegreen") +
  fur_tree(xstart = 320, length = 75, colour = "palegreen4") +
  fur_tree(xstart = 330, length = 120, colour = "palegreen4") +
  fur_tree(xstart = 350, length = 55, colour = "darkolivegreen") +
  fur_tree(xstart = 375, length = 40, colour = "darkolivegreen") +
  fur_tree(xstart = 390, length = 60, colour = "palegreen4") 

We remove a central section of trees to make space for the main Christmas tree.

furry_snowy_background <- snowy_background +
  fur_tree(xstart = 0, length = 50, colour = "palegreen4") +
  fur_tree(xstart = 20, length = 80, colour = "darkolivegreen") +
  fur_tree(xstart = 50, length = 75, colour = "palegreen4") +
  fur_tree(xstart = 100, length = 45, colour = "darkolivegreen") +
  fur_tree(xstart = 320, length = 75, colour = "palegreen4") +
  fur_tree(xstart = 330, length = 120, colour = "palegreen4") +
  fur_tree(xstart = 350, length = 55, colour = "darkolivegreen") +
  fur_tree(xstart = 375, length = 40, colour = "darkolivegreen") +
  fur_tree(xstart = 390, length = 60, colour = "palegreen4") 

furry_snowy_background

Christmas lights in the sky

We overlay decorative lights - curved lines in festive colours.

library(ggnewscale)
library(gganimate)

lights <- function(shift = 0, coef, col1, col2, col3) {
  
  pts <- NA
  x_coord <- c()
  y_coord <- c()
  colour <- c()
  cl <- NA
  
  cl <- rep(c("r", "b", "y"), 150)
  
  for (i in 1:450) {
    x_coord <- append(x_coord, i)
    y_coord <- append(y_coord, 450-coef*abs(sin((shift + i)/36)))
    
    if (i %% 5 == 0) {
      colour[i] <- cl [i]
    }
    else colour[i] <- "black"
    
    i = i + 1
  }
    
  pts <- data.frame(x_coord, y_coord, colour)
  
  light <- list(
    geom_line(data = pts, aes(x = x_coord, y = y_coord), colour = "grey2", linetype = "dotted"),
    geom_point(data = pts[pts$colour != "black",], aes(x = x_coord, y = y_coord, colour = colour), size = 2, alpha = 0.2),
    geom_point(data = pts[pts$colour != "black",], aes(x = x_coord, y = y_coord, colour = colour), size = 1.3, alpha = 0.45),
    geom_point(data = pts[pts$colour != "black",], aes(x = x_coord, y = y_coord, colour = colour), size = 0.5),
    scale_color_manual(values = c("y" = col1, "r" = col2, "b" = col3)),
    new_scale_color(),
    theme(legend.position = "none")
    )
  
  return(light)
}

happy_background <- furry_snowy_background +
  lights(shift = 0,  coef = 80, col1 = "yellow", col2 = "red", col3 = "blue") +
  lights(shift = 50, coef = 60, col1 = "red", col2 = "yellow", col3 = "green4")

happy_background

Fractal centerpiece

The main Christmas tree will be constructed as a geometric fractal built using an L-system and turtle graphics.

First, we have to define necessary functions to draw a fractal. I prompted ChatGPT to write an L-system generator and a function that turns the string into a “turtle” graphics coordinates. I further adapted and refined both functions, in order to create a fractal with the desired characteristics.

More about L-system and turtle graphics could be found from this excellent lecture.

l_system() — expands an L-system string for n iterations:

l_system <- function(axiom, rules, iter = 3) {
  current <- axiom
  for (i in seq_len(iter)) {
    chars <- strsplit(current, "")[[1]]
    next_str <- paste0(sapply(chars, function(ch) rules[[ch]] %||% ch), collapse = "")
    current <- next_str
  }
  current
}

`%||%` <- function(a, b) if (!is.null(a)) a else b

interpret_lsystem() — turns the string into turtle graphics coordinates:

lsystem_to_df <- function(xstart, ystart, string, angle, step) {
  angle_rad <- angle * pi/180
  
  # turtle state
  x <- xstart; y <- ystart
  dir <- 0     
  
  stack <- list()
  
  segs <- list()
  idx <- 1
  
  chars <- strsplit(string, "")[[1]]
  
  for (ch in chars) {
    if (ch == "A") {
      x_new <- x + step * cos(dir)
      y_new <- y + step * sin(dir)
      segs[[idx]] <- data.frame(x = round(x), y = round(y), xend = round(x_new), yend = round(y_new))
      idx <- idx + 1
      x <- x_new; y <- y_new
    } else if (ch == "+") {
      dir <- dir + angle_rad
    } else if (ch == "-") {
      dir <- dir - angle_rad
    } else if (ch == "[") {
      stack <- append(stack, list(list(x = x, y = y, dir = dir)))
    } else if (ch == "]") {
      state <- stack[[length(stack)]]
      stack <- stack[-length(stack)]
      x <- state$x; y <- state$y; dir <- state$dir
    }
  }
  
  do.call(rbind, segs)
}

Our Christmas tree will consists of four (perfect :)) Sierpinski triangles of different sizes stacked to form a silhouette of a tree.

iters <- 8 
rules <- list(
  "A" = "B-A-B",
  "B" = "A+B+A"
)
axiom <- "A"

ls <- l_system(axiom, rules, iters)

angle <- 60; step <- 2
tri1 <- lsystem_to_df(xstart = 100, ystart = 0, string = ls, angle = angle, step = step)

angle <- 60; step <- 1.5
tri2 <- lsystem_to_df(xstart = 100+2^5, ystart = 2^6*sqrt(3), string = ls, angle = angle, step = step)

angle <- 60; step <- 1.25
tri3 <- lsystem_to_df(xstart = 100+3*2^4, ystart = 7*2^4*sqrt(3), string = ls, angle = angle, step = step)

angle <- 60; step <- 1
tri4 <- lsystem_to_df(xstart = 100+2^6, ystart = 19*2^3*sqrt(3), string = ls, angle = angle, step = step)

sierpinski <- list(
  geom_segment(data = tri1, aes(x = x, y = y, xend = xend, yend = yend), linewidth = 0.4, color = "#0C4F22")
  ,geom_segment(data = tri2, aes(x = x, y = y, xend = xend, yend = yend), linewidth = 0.4, color = "#0C4F22")
  ,geom_segment(data = tri3, aes(x = x, y = y, xend = xend, yend = yend), linewidth = 0.3, color = "#0C4F22")
  ,geom_segment(data = tri4, aes(x = x, y = y, xend = xend, yend = yend), linewidth = 0.3, color = "#0C4F22")
  )

christmas_tree <- happy_background +
  sierpinski
christmas_tree

Embelishments onto the Christmas tree

The lights on the main tree:

lights2 <- function(x1, x2, y1, y2, colour) {
  pts <- NA
  
  x_coord = c(x1, x2)
  y_coord <- c(y1, y2)
    
  pts <- data.frame(x_coord, y_coord)
  
  lights <- list(
    geom_curve(data = pts, aes(x = x1, xend = x2, y = y1, yend = y2), linetype = "solid", colour = "gray", linewidth = 0.5, alpha = 0.5),
    geom_curve(data = pts, aes(x = x1, xend = x2, y = y1, yend = y2), linetype = "dotted", colour = colour, linewidth = 3, alpha = 0.7),
    geom_curve(data = pts, aes(x = x1, xend = x2, y = y1, yend = y2), linetype = "dotted", colour = "yellow", linewidth = 1)
  )
  
  return(lights)
}

happy_christmas_tree <- christmas_tree + 
  lights2(x1 = 145, x2 = 300, y1 = 80,  y2 = 210, colour="deeppink") +
  lights2(x1 = 165, x2 = 330, y1 = 180, y2 = 50,  colour="deeppink") +
  lights2(x1 = 165, x2 = 290, y1 = 180, y2 = 240, colour="deeppink") +
  lights2(x1 = 180, x2 = 290, y1 = 290, y2 = 240, colour="deeppink") +
  lights2(x1 = 180, x2 = 270, y1 = 290, y2 = 310, colour="deeppink") +
  lights2(x1 = 200, x2 = 270, y1 = 335, y2 = 310, colour="deeppink") +
  lights2(x1 = 200, x2 = 245, y1 = 335, y2 = 355, colour="deeppink") 

happy_christmas_tree

Presents under the tree

present <- function(x0, y0, w, h, colour_box, colour_bow)
{
  box <- NA
  ribbon_v <- NA
  ribbon_h <- NA
  
  box <- data.frame(x_coord = x0 + c(0, 0, w, w),
                    y_coord = y0 + c(0, h, h, 0))
  
  # ribbon width = 10% of the height
  ribbon_w <- w * 0.10
  
  ribbon_v <- data.frame(x_coord = x0 + c(w/2 - ribbon_w, w/2 - ribbon_w, w/2 + ribbon_w, w/2 + ribbon_w),
                         y_coord = y0 + c(0, h, h, 0))
  
  ribbon_h <- data.frame(x_coord = x0 + c(0, 0, w, w),
                         y_coord = y0 + c(h/2 - ribbon_w, h/2 + ribbon_w, h/2 + ribbon_w, h/2 - ribbon_w))
  
  bow_l <- data.frame(x_coord = x0 + c(0.5*w, 0.25*w, 0.15*w, 0.2*w),
                      y_coord = y0 + c(h, 1.5*h, 1.2*h, h))
  
  bow_r <- data.frame(x_coord = x0 + c(0.5*w, 0.75*w, 0.85*w, 0.8*w),
                      y_coord = y0 + c(h, 1.5*h, 1.2*h, h))
  
  gift <- list(
    geom_polygon(data = box,        aes(x_coord, y_coord), fill = colour_box, color = "black"),
    geom_polygon(data = ribbon_v,   aes(x_coord, y_coord), fill = colour_bow, color = "black"),
    geom_polygon(data = ribbon_h,   aes(x_coord, y_coord), fill = colour_bow, color = "black"),
    geom_polygon(data = bow_l,      aes(x_coord, y_coord), fill = colour_bow, color = "black"),
    geom_polygon(data = bow_r,      aes(x_coord, y_coord), fill = colour_bow, color = "black")
    )
  
  return(gift)
}

christmas_tree_with_gifts <- happy_christmas_tree +
  present(x0 = 0,   y0 = 0, w = 50, h = 50, colour_box = "red",      colour_bow = "gold1") +
  present(x0 = 50,  y0 = 0, w = 60, h = 60, colour_box = "green",    colour_bow = "cornsilk") +
  present(x0 = 110, y0 = 0, w = 50, h = 50, colour_box = "skyblue",  colour_bow = "yellow2") +
  present(x0 = 160, y0 = 0, w = 20, h = 20, colour_box = "red",      colour_bow = "darkgoldenrod1") +
  present(x0 = 180, y0 = 0, w = 20, h = 20, colour_box = "white",    colour_bow = "blueviolet") +
  present(x0 = 200, y0 = 0, w = 20, h = 20, colour_box = "chocolate1",   colour_bow = "firebrick1") +
  present(x0 = 220, y0 = 0, w = 30, h = 30, colour_box = "brown1",       colour_bow = "cadetblue3") +
  present(x0 = 250, y0 = 0, w = 50, h = 50, colour_box = "dodgerblue3",  colour_bow = "goldenrod") +
  present(x0 = 300, y0 = 0, w = 60, h = 60, colour_box = "coral",      colour_bow = "aliceblue") +
  present(x0 = 360, y0 = 0, w = 40, h = 40, colour_box = "red",      colour_bow = "blue") +
  present(x0 = 400, y0 = 0, w = 50, h = 50, colour_box = "white",    colour_bow = "deeppink3") 

christmas_tree_with_gifts

Greetings:

library(showtext)

## Loading required package: sysfonts

## Loading required package: showtextdb

font_add_google("Pacifico", "pacifico")
showtext_auto()

greet <- function(size, x, y, col1, col2, alpha=1){
  greeting <- list(
    annotate("text", x = x, y = y, family = "pacifico", size = size, label = "Merry", colour = col1)
    ,annotate("text", x = x, y = y-40, family = "pacifico", size = size, label = "Christmas", colour = col2)
    ,annotate("text", x = x, y = y-80, family = "pacifico", size = size, label = "and a Happy", colour = col1)
    ,annotate("text", x = x, y = y-120, family = "pacifico", size = size, label = "New Year!", colour = col2)
  )
}

greetings <- christmas_tree_with_gifts +
   greet(size=10, x = 79, y = 319, col1 = "white", col2 = "white", alpha = 0.8) +
   greet(size=10, x = 80, y = 320, col1 = "darkgreen", col2 = "red2")

greetings