R/zzz.R

In rvtk: Bindings for the Visualization Toolkit ('VTK')

# Package hooks --------------------------------------------------------

## Saved PATH value before rvtk prepended the vtk-dlls directory.
## Used by .onUnload to restore PATH cleanly.
.vtk_original_path <- NULL

.onLoad <- function(libname, pkgname) {
  ## On Windows, if rvtk was installed against a shared VTK build, the VTK
  ## DLLs are staged in inst/vtk-dlls/.  Prepend that directory to PATH so
  ## that the Windows DLL loader can find the VTK DLLs when downstream
  ## packages that link against them are loaded.
  ##
  ## For system VTK installs (e.g. pacman ucrt64), also prepend VTK_DLL_DIR
  ## (the original bin/ of the system VTK, e.g. C:/rtools45/ucrt64/bin) so
  ## that transitive dependencies of the VTK DLLs (libtbb, libgcc_s, etc.)
  ## which live there can also be found by the Windows DLL loader.
  ##
  ## R's own library.dynam() uses the same Sys.setenv(PATH=...) mechanism
  ## (see src/library/base/R/library.R), and the dyn.load() help page
  ## documents this as the standard approach.  The Windows DLL loader
  ## searches PATH as part of its resolution chain; R's newer
  ## SetDllDirectory / AddDllDirectory calls are not exposed at the R level.
  ##
  ## We save the original PATH so that .onUnload() can restore it, which
  ## satisfies CRAN's requirement that packages not leave persistent side
  ## effects after being unloaded.
  if (.Platform$OS.type == "windows") {
    conf <- tryCatch(read_vtk_conf(), error = function(e) NULL)

    ## Directory containing staged VTK DLLs (always present for shared builds)
    dll_dir <- system.file("vtk-dlls", package = pkgname, lib.loc = libname)

    ## Original system VTK bin/ dir (present for system-VTK shared builds only)
    vtk_dll_dir <- if (!is.null(conf)) conf[["VTK_DLL_DIR"]] else NULL

    dirs_to_add <- character(0L)
    if (nzchar(dll_dir) && dir.exists(dll_dir)) {
      dirs_to_add <- c(
        normalizePath(dll_dir, winslash = "\\", mustWork = FALSE),
        dirs_to_add
      )
    }
    if (!is.null(vtk_dll_dir) && nzchar(vtk_dll_dir)) {
      dirs_to_add <- c(
        dirs_to_add,
        normalizePath(vtk_dll_dir, winslash = "\\", mustWork = FALSE)
      )
    }

    if (length(dirs_to_add) > 0L) {
      old_path <- Sys.getenv("PATH")
      new_dirs <- dirs_to_add[
        !vapply(
          dirs_to_add,
          function(d) grepl(d, old_path, fixed = TRUE),
          logical(1L)
        )
      ]
      if (length(new_dirs) > 0L) {
        ns <- environment(sys.function())
        assign(".vtk_original_path", old_path, envir = ns)
        Sys.setenv(
          PATH = paste(
            paste(new_dirs, collapse = ";"),
            old_path,
            sep = ";"
          )
        )
      }
    }
  }
}

.onUnload <- function(libpath) {
  ## Restore PATH to the value it had before .onLoad prepended vtk-dlls,
  ## so that unloading rvtk leaves no persistent side effects.
  if (.Platform$OS.type == "windows") {
    ns <- asNamespace("rvtk")
    saved <- get0(".vtk_original_path", envir = ns, inherits = FALSE)
    if (!is.null(saved)) {
      Sys.setenv(PATH = saved)
    }
  }
}