Transform mouse emoji into cat emoji

mouse_to_cat.R

library(tidyverse)
library(fontr)
library(emojifont)
library(ggpolypath)
library(transformr)
library(animation)
library(Cairo)

# create the base images from cat emoji and mouse emoji!
cat <- glyph_polygon(ch = emoji("cat"), family = "EmojiOne")
mouse <- glyph_polygon(ch = emoji("mouse"), family = "EmojiOne")

# function to stitch two tweens together
bind_tweens <- function(forward, backward) {
  nframes <- max(forward$.frame)
  backward <- backward %>% mutate(.frame = .frame + nframes)
  anim <- bind_rows(forward, backward)
  return(anim)
}

# function to tween from one image to another then back
loop <- function(from, to, by, ...) {
  forward <- by(from, to, ...)
  backward <- by(to, from, ...)
  return(bind_tweens(forward, backward))
}

# function to draw a frame
drawframe <- function(data, f) {
  df <- data %>%
    filter(.frame == f)
  df$branch <- is.na(df$x)
  df$branch <- cumsum(df$branch) + 1
  pic <- df %>%
    filter(!is.na(x)) %>%
    ggplot(aes(x=x, y=y, group=branch)) +
    geom_polypath(show.legend = FALSE,
                  fill="black", alpha = .5) +
    xlim(-.5,1) +
    ylim(-.5,1) +
    coord_equal() +
    theme_void()
  plot(pic)
}

# construct the anumation
anim <- loop(mouse, cat, tween_path,
             ease = "cubic-in-out", nframes = 50)

# save it
saveGIF(
  expr = {
    for(f in 1:100) drawframe(anim, f)
  },
  movie.name = "~/../Desktop/mouse_to_cat.gif",
  interval = .05,
  ani.dev = "CairoPNG"
)