Replacing the demo video

R/demo.R

@@ -8,20 +8,77 @@
 #' @param ... other parameters passed to [av_capture_graphics].
 #' @name demo
 #' @family av
-av_demo <- function(output = "demo.mp4", width = 960, height = 720, framerate = 5, verbose = TRUE, ...){
-  wonderland <- system.file('samples/Synapsis-Wonderland.mp3', package='av', mustWork = TRUE)
-  info <- av_video_info(wonderland)
+av_demo <- function(output = "demo.mp4", width = 960, height = 720, framerate = 24, verbose = TRUE, ...){
+
+  # Attribution:
+  # Big Horns Intro by Audionautix is licensed under a Creative Commons Attribution license
+  # (https://creativecommons.org/licenses/by/4.0/)
+  # Artist: http://audionautix.com/
+  big_horns_intro <- system.file('samples/Big_Horns_Intro.mp3', package='av', mustWork = TRUE)
+  info <- av_video_info(big_horns_intro)
   len <- framerate * round(info$duration)
   res <- round(72 * min(width, height) / 480)
 
-  # RColorBrewer::brewer.pal(12,"Set3")
-  col <- c("#8DD3C7", "#FFFFB3", "#BEBADA", "#FB8072", "#80B1D3", "#FDB462",
-    "#B3DE69", "#FCCDE5", "#D9D9D9", "#BC80BD", "#CCEBC5", "#FFED6F")
-  video <- av_capture_graphics(output = output,  audio = wonderland, {
+  # Himmelblau's function: https://en.wikipedia.org/wiki/Himmelblau%27s_function
+  f <- function(x, y) { (x^2+y-11)^2 + (x+y^2-7)^2 }
+
+  x <- seq(-6, 6, length = 100)
+  y <- x
+  z <- outer(x, y, f)
+
+  # partial derivatives
+  dx <- function(x,y) {4*x**3-4*x*y-42*x+4*x*y-14}
+  dy <- function(x,y) {4*y**3+2*x**2-26*y+4*x*y-22}
+
+  # gradient descent parameters
+  num_iter <- len
+  learning_rate <- 0.0005
+  x_val <- 6
+  y_val <- 6
+
+  # momentum parameters
+  beta = 0.95
+  vdx = 0
+  vdy = 0
+
+  updates_x <- vector("numeric", length = num_iter)
+  updates_y <- vector("numeric", length = num_iter)
+  updates_z <- vector("numeric", length = num_iter)
+
+  # parameter updates
+  for (i in 1:num_iter) {
+
+    vdx = beta*vdx+dx(x_val,y_val)
+    vdy = beta*vdy+dy(x_val,y_val)
+
+    x_val <- x_val-learning_rate*vdx
+    y_val <- y_val-learning_rate*vdy
+    z_val <- f(x_val, y_val)
+
+    updates_x[i] <- x_val
+    updates_y[i] <- y_val
+    updates_z[i] <- z_val
+  }
+
+  video <- av_capture_graphics(output = output,  audio = big_horns_intro, {
     for(i in seq_len(len)){
       if(as.logical(verbose))
         cat(sprintf("\rGenerating plot %d/%d...", i, len), file = stderr())
-      graphics::hist(stats::rnorm(100), col = col, main = sprintf("frame %d/%d", i, len))
+
+
+      plt <- persp(x, y, z,
+                   theta = -50-i*0.2, phi = 20+log(i),
+                   expand = 0.5,
+                   col = "lightblue", border = 'lightblue',
+                   axes = FALSE, box = FALSE,
+                   ltheta = 60, shade = 0.90
+      )
+
+      points(trans3d(updates_x[1:i], updates_y[1:i], updates_z[1:i], pmat = plt), pch = 16,
+             cex = c(rep(0.6, i-1), 1.2),
+             col = c(rep('white', i-1), 'black')
+      )
+
     }
     if(as.logical(verbose))
       cat("done!\n", file = stderr())

README.md

@@ -27,14 +27,16 @@ devtools::install_github("thomasp85/gganimate")
 
 ## Demo Video
 
-Generate a demo video with some random plots and free [demo music](https://freemusicarchive.org/music/Synapsis/~/Wonderland):
+Generate a demo video with some random plots and free [demo music](https://www.youtube.com/watch?v=35sTb_c7fJI):  
+
+Music in the demo video:  
+Big Horns Intro by Audionautix is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/)  
+Artist: http://audionautix.com/
 
 ```r
 av::av_demo()
 ```
 
-This demo is totally lame, please open a PR with something better (in base R!).
-
 ## Using gganimate
 
 You can use `av_encode_video()` as the renderer in gganimate:

tests/testthat/test-video.R

@@ -39,10 +39,10 @@ test_that("convert images into video formats", {
 })
 
 test_that("audio sampling works", {
-  wonderland <- system.file('samples/Synapsis-Wonderland.mp3', package='av', mustWork = TRUE)
+  big_horns_intro <- system.file('samples/Big_Horns_Intro.mp3', package='av', mustWork = TRUE)
   for(ext in c("mkv", "mp4", "mov", "flv")){
     filename <- paste0("test.", ext)
-    av::av_encode_video(png_files, filename, framerate = framerate, verbose = FALSE, audio = wonderland)
+    av::av_encode_video(png_files, filename, framerate = framerate, verbose = FALSE, audio = big_horns_intro)
     expect_true(file.exists(filename))
     info <- av_video_info(filename)
     unlink(filename)