7  GUI consoles

The standard R front-ends are programs which run in a terminal, but there are several ways to provide a GUI console.

This can be done by a package which is loaded from terminal-based R and launches a console as part of its startup code or by the user running a specific function: package Rcmdr is a well-known example with a Tk-based GUI.

There used to be a Gtk-based console invoked by R --gui=GNOME: this relied on special-casing in the front-end shell script to launch a different executable. There still is R --gui=Tk, which starts terminal-based R and runs tcltk::tkStartGui() as part of the modified startup sequence.

However, the main way to run a GUI console is to launch a separate program which runs embedded R: this is done by Rgui.exe on Windows and R.app on macOS. The first is an integral part of R and the code for the console is currently in R.dll.

7.1 R.app

R.app is a macOS application which provides a console. Its sources are a separate project1, and its binaries link to an R installation which it runs as a dynamic library libR.dylib. The standard CRAN distribution of R for macOS bundles the GUI and R itself, but installing the GUI is optional and either component can be updated separately.

R.app relies on libR.dylib being in a specific place, and hence on R having been built and installed as a Mac macOS ‘framework’. Specifically, it uses /Library/Frameworks/R.framework/R. This is a symbolic link, as frameworks can contain multiple versions of R. It eventually resolves to /Library/Frameworks/R.framework/Versions/Current/Resources/lib/libR.dylib, which is (in the CRAN distribution) a ‘fat’ binary containing multiple sub-architectures.

macOS applications are directory trees: each R.app contains a front-end written in Objective-C for one sub-architecture: in the standard distribution there are separate applications for 32- and 64-bit Intel architectures.

Originally the R sources contained quite a lot of code used only by the macOS GUI, but this was migrated to the R.app sources.

R.app starts R as an embedded application with a command-line which includes --gui=aqua (see below). It uses most of the interface pointers defined in the header Rinterface.h, plus a private interface pointer in file src/main/sysutils.c. It adds an environment it names tools:RGUI to the second position in the search path. This contains a number of utility functions used to support the menu items, for example package.manager(), plus functions q() and quit() which mask those in package base—the custom versions save the history in a way specific to R.app.

There is a configure option --with-aqua for R which customizes the way R is built: this is distinct from the --enable-R-framework option which causes make install to install R as the framework needed for use with R.app. (The option --with-aqua is the default on macOS.) It sets the macro HAVE_AQUA in config.h and the make variable BUILD_AQUA_TRUE. These have several consequences:

  • The quartz() device is built (other than as a stub) in package grDevices: this needs an Objective-C compiler. Then quartz() can be used with terminal R provided the latter has access to the macOS screen.
  • File src/unix/aqua.c is compiled. This now only contains an interface pointer for the quartz() device(s).
  • capabilities("aqua") is set to TRUE.
  • The default path for a personal library directory is set as ~/Library/R/arch/x.y/library.
  • There is support for setting a ‘busy’ indicator whilst waiting for system() to return.
  • R_ProcessEvents is inhibited in a forked child from package parallel. The associated callback in R.app does things which should not be done in a child, and forking forks the whole process including the console.
  • There is support for starting the embedded R with the option --gui=aqua: when this is done the global C variable useaqua is set to a true value. This has consequences:
    • The R session is asserted to be interactive via R_Interactive.
    • .Platform$GUI is set to "AQUA". That has consequences:
      • The environment variable DISPLAY is set to :0 if not already set.
      • /usr/local/bin is appended to PATH since that is where gfortran is installed.
      • The default HTML browser is switched to the one in R.app.
      • Various widgets are switched to the versions provided in R.app: these include graphical menus, the data editor (but not the data viewer used by View()) and the workspace browser invoked by browseEnv().
      • The grDevices package when loaded knows that it is being run under R.app and so informs any quartz devices that a Quartz event loop is already running.
    • The use of the OS’s system function (including by system() and system2(), and to launch editors and pagers) is replaced by a version in R.app (which by default just calls the OS’s system with various signal handlers reset).
  • If either R was started by --gui=aqua or R is running in a terminal which is not of type dumb, the standard output to files stdout and stderr is directed through the C function Rstd_WriteConsoleEx. This uses ANSI terminal escapes to render lines sent to stderr as bold on stdout.
  • For historical reasons the startup option -psn is allowed but ignored. (It seems that in 2003, r27492, this was added by Finder.)

Footnotes