Animating Patterns with gganimate

library("ggplot2")
library("ggpattern")
library("gganimate")

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Create a dataset with 2 different states
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
df1 <- data.frame(time = 1, offset = 0    , trt = c("a", "b", "c"), outcome = c(2.3, 1.9, 3.2), stringsAsFactors = FALSE)
df2 <- data.frame(time = 2, offset = 0.045, trt = c("a", "b", "c"), outcome = c(2.3, 1.9, 3.2), stringsAsFactors = FALSE)
df  <- rbind(df1, df2)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Plot the two different states and transition between them.
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
p <- ggplot(df, aes(trt, outcome)) +
  geom_col_pattern(
    aes(
      pattern_fill    = trt,
      pattern_xoffset = offset,
      pattern_yoffset = -offset
    ),
    colour          = "black",
    fill            = "white",
    pattern_density = 0.5,
    pattern_angle   = 45
  ) +
  theme_bw() +
  labs(title = "ggpattern + gganimate") +
  theme(legend.position = "none") +
  coord_fixed(ratio = 1/2)

p <- p + transition_states(time, transition_length = 2,
                    state_length = 0, wrap = FALSE)

animate(p, nframes = 60, fps = 20)