Using gganimate to create an animation of fireworks over a background image

fireworks.R

## following https://alistaire.rbind.io/blog/fireworks/
## but manually convert to polar coordinates to be able to add
## background image, which cannot be used with coord_polar()

library(ggplot2)
library(gganimate)
theme_set(theme_void())

## create set of points in polar coordinates
set.seed(0)
data <- expand.grid(
  r = seq(5)-0.9, ## 5 rings starting from r=0.1 to r=4.1
  theta = runif(50, 0, 360) * pi / 180 ## 30 randomly distributed particles per ring
)

## convert from polar coordinates to cartesian for plotting
data_polar <- data.frame(x = data$r * cos(data$theta), 
                         y = data$r * sin(data$theta))

## add time for animation later
data_polar$t <- rep(1:5, 50) ## time for animation

## plot with ggplot
g <- ggplot(data_polar) + 
  geom_point(aes(x,y,col=t)) 
g

## add a background_image
library(ggpubr)
library(png)
## download and modify from
## https://www.freepik.com/free-vector/cityscape-night_2987104.htm
url <- "background.png"
bg_image <- readPNG(url)
gg <- ggplot(data_polar) +
  background_image(bg_image) + 
  geom_point(aes(x,y,col=t)) + 
  scale_color_gradient(low="white", high="#f8eca4") + 
  guides(color = FALSE) +
  xlim(-8.5,8.5) + ylim(-12,5) 
gg

## animate
p <- gg +  
  transition_time(t) + 
  shadow_wake(1) ## make firework trail longer
animate(p, fps = 100, nframes = 30)