fixes misalignment between ggsave and animate

DESCRIPTION

@@ -46,7 +46,8 @@ Suggests:
     rmarkdown,
     sf,
     svglite,
-    testthat
+    testthat,
+    xml2
 VignetteBuilder: 
     knitr
 Encoding: UTF-8

R/animate.R

@@ -246,32 +246,21 @@ prerender <- function(plot, nframes) {
 draw_frames <- function(plot, frames, device, ref_frame, ...) {
   stream <- device == 'current'
 
-  dims <- try_fetch(
-    plot_dims(plot, ref_frame),
-    error = function(e) {
-      cli::cli_warn('Cannot get dimensions of plot table. Plot region might not be fixed', parent = e)
-      list(widths = NULL, heights = NULL)
-    }
-  )
-
-  dir <- tempfile(pattern = '')
-  dir.create(dir, showWarnings = FALSE)
-  files <- file.path(dir, sprintf('gganim_plot%04d', seq_along(frames)))
-  files <- switch(
+  ext <- switch(
     tolower(device),
     ragg_png = ,
-    png = paste0(files, '.png'),
+    png = '.png',
     jpg = ,
-    jpeg = paste0(files, '.jpg'),
+    jpeg = '.jpg',
     tif = ,
-    tiff = paste0(files, '.tif'),
-    bmp = paste0(files, '.bmp'),
+    tiff = '.tif',
+    bmp = '.bmp',
     svglite = ,
-    svg = paste0(files, '.svg'),
-    current = files,
+    svg = '.svg',
+    current = '',
     cli::cli_abort('Unsupported device: {device}')
   )
-  device <- switch(
+  device_fn <- switch(
     device,
     ragg_png = ragg::agg_png,
     png = png,
@@ -281,10 +270,25 @@ draw_frames <- function(plot, frames, device, ref_frame, ...) {
     tiff = tiff,
     bmp = bmp,
     svg = svg,
-    svglite = svglite::svglite
+    svglite = svglite::svglite,
+    current = png
   )
   args <- list(...)
-  args <- args[names(args) %in% names(formals(device))]
+  args <- args[names(args) %in% names(formals(device_fn))]
+
+  dims <- try_fetch(
+    plot_dims(plot, ref_frame, device = device_fn, dev_args = args),
+    error = function(e) {
+      cli::cli_warn('Cannot get dimensions of plot table. Plot region might not be fixed', parent = e)
+      list(widths = NULL, heights = NULL)
+    }
+  )
+
+  dir <- tempfile(pattern = '')
+  dir.create(dir, showWarnings = FALSE)
+  files <- file.path(dir, sprintf('gganim_plot%04d', seq_along(frames)))
+  files <- if (stream) files else paste0(files, ext)
+  device <- device_fn
 
   pb <- progress_bar$new(
     'Rendering [:bar] at :fps fps ~ eta: :eta',
@@ -316,9 +320,9 @@ draw_frames <- function(plot, frames, device, ref_frame, ...) {
   frame_vars
 }
 # Get dimensions of plot based on a reference frame
-plot_dims <- function(plot, ref_frame) {
+plot_dims <- function(plot, ref_frame, device = png, dev_args = list()) {
   tmpf <- tempfile()
-  png(tmpf)
+  inject(device(tmpf, !!!dev_args))
   on.exit({
     dev.off()
     unlink(tmpf)

R/scene.R

@@ -158,7 +158,7 @@ Scene <- ggproto('Scene', NULL,
       })
       if (orig_call) {
         new_label[[1]]
-      } else if (is_expression(label)) {
+      } else if (is.expression(label)) {
         as.expression(new_label)
       } else {
         unlist(new_label)

tests/testthat/test-ggplot-align.R

@@ -0,0 +1,68 @@
+context("ggplot alignment")
+
+# Helper: parse y-coordinates of text elements from an SVG file.
+# Returns a named list with entries for elements matching each selector pattern.
+svg_text_y <- function(svg_path) {
+  xml <- xml2::read_xml(svg_path)
+  xml2::xml_ns_strip(xml)
+  nodes <- xml2::xml_find_all(xml, "//text")
+  y_vals <- as.numeric(xml2::xml_attr(nodes, "y"))
+  y_vals[!is.na(y_vals)]
+}
+
+test_that("animate and ggsave produce the same layout with svg device", {
+  skip_if_not_installed("xml2")
+  skip_if_not_installed("svglite")
+
+  df <- data.frame(
+    x = rep(1:5, 2),
+    y = c(1:5, 5:1),
+    state = rep(1:2, each = 5)
+  )
+
+  base_plot <- ggplot(df, aes(x, y)) +
+    labs(title = "Title", subtitle = "Subtitle", caption = "Caption") +
+    theme_minimal(base_size = 14) +
+    scale_x_continuous(limits = c(0, 6)) +
+    scale_y_continuous(limits = c(0, 6))
+
+  # ggsave reference: render state 1 directly
+  ggplot_svg <- tempfile(fileext = ".svg")
+  ggplot2::ggsave(
+    plot = ggplot(subset(df, state == 1), aes(x, y)) +
+      geom_point() +
+      labs(title = "Title", subtitle = "Subtitle", caption = "Caption") +
+      theme_minimal(base_size = 14) +
+      scale_x_continuous(limits = c(0, 6)) +
+      scale_y_continuous(limits = c(0, 6)),
+    filename = ggplot_svg,
+    device = svglite::svglite,
+    width = 5, height = 5
+  )
+
+  # animate: render state 1 frame via gganimate with svglite device
+  anim <- base_plot +
+    geom_point() +
+    transition_states(state, wrap = FALSE)
+
+  frame_paths <- animate(
+    anim,
+    renderer = function(frames, fps) frames,
+    nframes = 2,
+    fps = 1,
+    device = "svglite",
+    width = 5,
+    height = 5,
+    units = "in"
+  )
+
+  gganimate_svg <- frame_paths[[1]]
+
+  ggplot_y  <- svg_text_y(ggplot_svg)
+  gganimate_y <- svg_text_y(gganimate_svg)
+
+  # Both renders should produce the same number of text elements at the same
+  # y-positions (within floating-point tolerance).
+  expect_equal(length(ggplot_y), length(gganimate_y))
+  expect_equal(ggplot_y, gganimate_y, tolerance = 0.5)
+})