Appendix C — Stained Glass Heart

I’ve been inspired by a lot of the charts I see on the #30DayChartChallenge hashtag, but Icaro Bernardes` stained glass was the first I wanted to make my own. His original code shows how to create a gorgeous stained-glass window with text. I’ve simplified the code a bit and am just making a heart (using maths) in stained glass.

Setup

library(ggplot2) # for plotting
library(dplyr)   # for data wrangling
library(sf)      # for shapes
library(ggforce) # for voronoi tiles

C.1 Variables

First, set up some variables, like a seed to use for the random elements, the number of points (more will make the glass pieces smaller), and your base palette (I’m using the psyTeachR rainbow colours).

Variables

seed <- 8675309
n_pts <- 150 ### Number of points to try to put inside the window
palette <- c(
  "pink" = "#983E82",
  "orange" = "#E2A458",
  "yellow" = "#F5DC70",
  "green" = "#59935B",
  "blue" = "#467AAC",
  "purple" = "#61589C"
)

C.2 Frame

Make a matrix of the x and y coordinates of the frame. The code below is the maths for a heart.

heart frame

t <- seq(0, 2*pi, by=0.05)
t <- c(t, t[[1]]) # append starting value
frame <- cbind(
  16*sin(t)^3,
  13*cos(t)-5*cos(2*t)-2*cos(3*t)-cos(4*t)
)

Then convert the matrix to a polygon. Plot to check it looks right.

convert to a polygon

frame_sf <- frame %>%
  list() %>% 
  sf::st_polygon()

ggplot(frame_sf) + geom_sf()

C.3 Random points

Make some random points within the range of x and y values of the frame.

random data points in frame bounds

set.seed(seed)
points <- tibble(
  x = runif(n_pts, min = min(frame[,1]), max = max(frame[,1])),
  y = runif(n_pts, min = min(frame[,2]), max = max(frame[,2]))
)

# plot to check
ggplot() + 
  geom_sf(data = frame_sf) +
  geom_point(aes(x, y), points)

C.4 Constrain points

Constrain the points to just those inside the frame. Do this by creating an sf version of the points, then using sf::st_contains() to check which are contained in the frame sf object. Then, select just the contained points from the points table.

constrain points

## Creates a new sf object to hold the created points
points_sf <- sf::st_as_sf(points, coords = c("x","y"))

## Keeps only the random points that are within the frame
contained <- sf::st_contains(frame_sf, points_sf)
points <- points %>% dplyr::slice(contained[[1]])

# plot to check
ggplot() + 
  geom_sf(data = frame_sf) +
  geom_point(aes(x, y), points)

C.5 Pane colours

Add to the points table a column called fill with randomly sampled colours from the paletteand a column calledalpha` with randomly sampled values between 0.2 and 0.9. You can change these to make your window more or less transparent.

pane colours

set.seed(seed)
points <- points %>% 
  mutate(
    fill = sample(palette, nrow(.), T),
    alpha = runif(nrow(.), min = 0.2, max = 0.9)
  )

C.6 Plot

Now plot! Note the I() function for fill and alpha, which uses the actual value in these columns, instead of mapping new values to each unique value.

Plot

ggplot(points) +
  geom_voronoi_tile(aes(x = x, y = y, 
                        group = -1L, 
                        fill = I(fill),
                        alpha = I(alpha)),
                    color = "black", 
                    size = 1.5, 
                    bound = frame) +
  geom_sf(data = frame_sf, 
          size = 4, 
          color = "grey10", 
          fill = "transparent") +
  theme_void()

I like it even better with a black background.

Black heart

ggplot2::last_plot() +
  theme(plot.background = element_rect(fill = "black"))