Eselect (OpenGL) (also called eselect-opengl) is a module for Eselect that allows the OpenGL implementation on a Funtoo Linux or Gentoo Linux system to be switched between a variety of installed OpenGL implementations. It functions by creating an env.d file at /etc/env.d/03opengl which contains OpenGL settings, as well as managing symbolic links to OpenGL libraries and headers.
Sample env.d File
A sample env.d file for a multilib system with xorg-x11 OpenGL implementation may look like this:
Eselect-opengl is implemented as a single bash-based Eselect module approximately 10K in size, installed at /usr/share/eselect/modules/opengl.eselect. One interfaces with this module via the main eselect command:
# eselect opengl help Manage the OpenGL implementation used by your system Usage: eselect opengl <action> <options> Standard actions: help Display help text usage Display usage information version Display version information Extra actions: list List the available OpenGL implementations. set <target> Select the OpenGL implementation. <target> The profile to activate --use-old If an implementation is already set, use that one instead --prefix=<val> Set the source prefix (default: /usr) --dst-prefix=<val> Set the destination prefix (default: /usr) --ignore-missing Ignore missing files when setting a new implementation show Print the current OpenGL implementation.
What is Switched
Using eselect opengl set causes the following symbolic links to be updated to point to the files corresponding to the OpenGL implementation that you chose:
- Libraries (32-bit and 64-bit):
- C Headers:
The symbolic links point to an installed OpenGL implementation, stored inside /usr/lib(32|64|)/opengl/(implementation-name). These files are structured as follows:
On multilib systems, ebuilds that provide an OpenGL implementation install 32-bit libraries in /usr/lib32/opengl/(implementation name)/lib and 64-bit libraries in /usr/lib64/opengl/(implementation name)/lib.
Violation of Build Consistency
As documented in Bug FL-1309, sometimes packages fail to merge when the "wrong" eselect opengl implementation is selected. This violates Portage's ability to consistently build a package from source, assuming all its dependencies are satisfied. This could be classified as a design bug -- eselect-opengl is functioning as intended, but its underlying theory of operation is not correct.
A possible solution to this problem, discussed in Bug FL-1309, is to redesign eselect-opengl to only select the runtime OpenGL implementation, but to have all ebuilds build against the official xorg-x11 OpenGL implementation.
The rationale for this design change is that:
- There should be a consistent and repeatable build/linking process for all OpenGL applications.
- AMD and NVIDIA implementations of OpenGL are designed to be more of a "drop-in" runtime replacement for xorg-x11, rather than a standalone replacement for xorg-x11, and thus appear to exhibit more build-time bugs.