Generate and animate snow -- https://twitter.com/ikashnitsky/status/1203302446753300480

animated-snowflakes.R

#===============================================================================
# 2019-12-07 -- twitter
# Generate snow and animate it
# Ilya Kashnitsky, ilya.kashnitsky@gmail.com
#===============================================================================

library(tidyverse)
library(magrittr)
library(gganimate)


# generate the init df
n <- 1e2

df <- tibble(
    id = 1:n,
    x = runif(n),
    y = runif(n),
    size = runif(n, min = 4, max = 20)
) 




# helper function to ensure the snowflakes don't disappear ----------------

# function for one snowflake
loop_single <- function(value){
    if(value %>% is_less_than(0)){value <- 1}
    if(value %>% is_greater_than(1)){value <- 0}
    return(value)
}

# vectorize
loop_multiple <- function(values){
    values %>% map_dbl(loop_single)
}



# create a larger dataframe with frames for snowflake movement ------------


# function to create smooth frames for snowflake falling
fun_framing <- function(df, n_frames = 100, wind = 0){
    
    # frames vector
    frames <- seq(1, n_frames)
    
    # empty list
    out <- list()
    
    # place the init df in the first element
    out[[1]] <- df
    
    # length of the df
    len <- nrow(df)

    
    for (i in seq_along(frames)) {
        
        # calculate x shift,  unique for each snowflake
        x_shift <- runif(len, -.5, .5) %>% add(wind)
        
        dfi <- out[[i]] %>% 
            mutate(
                x = x %>% 
                    add(x_shift %>% multiply_by(size/1e3)) %>% 
                    loop_multiple(),
                y = y %>% 
                    subtract(size/1e3) %>% 
                    loop_multiple()
            ) 
        out[[i+1]] <- dfi
    }
    
    # bind list
    out <- out %>% 
        bind_rows(.id = "frame") %>% 
        mutate(frame = frame %>% as.numeric)
    return(out)
}


# generate the data and plot/animate --------------------------------------

# generate df for animation    
df_anim <- df %>% fun_framing(n_frames = 1e2, wind = -1)


# plot to animate
p <- df_anim %>% 
    ggplot(aes(x, y, size = size)) + 
    geom_point(color = "white", shape = 42)+
    scale_size_identity()+
    coord_cartesian(c(0, 1), c(0, 1), expand = FALSE)+
    theme_void()+
    theme(panel.background = element_rect(fill = "black"),
          plot.background = element_rect(fill = "black"))

# add transition
ani <- p + 
    transition_time(frame)+ 
    ease_aes('linear')+
    enter_fade()+
    exit_fade()

# define the number of data points
nfr <- df_anim %>% pull(frame) %>% unique() %>% length()

# animate
animate(
    ani, 
    nframes = nfr, fps = 10, 
    # device = "svg", renderer = magick_renderer(loop = TRUE),
    width = 500, height = 500
)

# save the output
anim_save("animated-snow.gif")