grid.grab() captures all of the current viewports and stores them as a grob. In theory, and often in practice, you can use grid.grab() to store an image now for drawing later on. But I have noticed some odd behavior of grid.grab() when working with lattice output. It is all related to the wrap argument:
1. When wrap = TRUE, the saved grob should produce a drawing faithful to the original viewports. But sometimes it doesn't. 2. wrap = FALSE is supposed to produce less faithful output if it differs at all, but sometimes its output is more faithful. 3. Even when using wrap = TRUE, grid.grab() warns me to use wrap = TRUE. Here is a minimal example to illustrate all of these behaviors: library(grid) library(lattice) xyplot(1:5 ~ 1:5) trellis.focus() panel.abline(h = 3) panel.abline(h = 5) myGrob <- grid.grab(wrap = TRUE) At this point, I receive a warning -- In grabDL(warn, wrap, ...) : one of more grobs overwritten (grab WILL not be faithful; try 'wrap = TRUE') -- which is strange, given that I specified wrap = TRUE. I proceed by running grid.draw(myGrob). According to Paul Murrell (R Graphics, 2nd ed., page 239), using grid.grab(wrap = TRUE) is "guaranteed to replicate the original output." But it doesn't. Specifically, the top horizontal line (from panel.abline(h = 5)) isn't reproduced. Matters get stranger when I consider the following code: xyplot(1:5 ~ 1:5) trellis.focus() panel.abline(h = 3) panel.abline(h = 5) myGrob <- grid.grab(wrap = FALSE) grid.draw(myGrob) These commands are the same as in the previous example, except that this time, wrap = FALSE. But this time, grid.draw() does faithfully reproduce the captured viewports. So the behavior is the opposite of what I expect: when wrap = FALSE, grid.draw() faithfully reproduces the captured viewports, but when wrap = TRUE, it doesn't. I've run these examples in R 3.3.2 and 3.5.1. (Session info from 3.3.2 is appended.) The result is the same in both cases. Are these bugs, or am I overlooking something? Thank you, John Bullock > sessionInfo() R version 3.3.2 (2016-10-31) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows 10 x64 (build 17134) locale: [1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252 LC_MONETARY=English_United States.1252 LC_NUMERIC=C [5] LC_TIME=English_United States.1252 attached base packages: [1] grid stats graphics grDevices utils datasets methods base other attached packages: [1] lattice_0.20-34 RevoUtilsMath_10.0.0 loaded via a namespace (and not attached): [1] RevoUtils_10.0.2 [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.