Package:Eselect (OpenGL)

Eselect (OpenGL)

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Introduction

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. A sample env.d file for a multilib system with xorg-x11 OpenGL implementation may look like this:

   /etc/env.d/03opengl - An example env.d file for eselect-opengl

# Configuration file for eselect
# This file has been automatically generated.
LDPATH="/usr/lib32/opengl/xorg-x11/lib:/usr/lib64/opengl/xorg-x11/lib"
OPENGL_PROFILE="xorg-x11"

Implementation

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:

root # eselect opengl help
Manage the OpenGL implementation used by your system
Usage: eselect opengl <action> <options>

root ##g##Standard actions:
  help                      Display help text
  usage                     Display usage information
  version                   Display version information

root ##g##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

Eselect-opengl handles switching of the active:

• Libraries (32-bit and 64-bit):
  • libGL
  • libEGL
  • libGLESv1
  • libGLESv2
• C Headers:
  • /usr/include/GL/*
  • /usr/include/EGL/*
  • /usr/include/KHR/*
• libglx.so

Ebuilds that provide an active OpenGL implementation install their libraries, headers, etc. in:

• /usr/lib/opengl/(implementation-name)/lib
• /usr/lib/opengl/(implementation-name)/include
• /usr/lib/opengl/(implementation-name)/extensions/libglx.so

On multilib systems, 32-bit libraries are installed to /usr/lib32/opengl/(implementation name)/lib and 64-bit libraries are installed to /usr/lib64/opengl/(implementation name)/lib.

Eselect-opengl looks in these directories for active OpenGL implementations.

Criticisms

Violation of Build Consistency

As documented in 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.

Possible Solutions

A possible solution to this problem, discussed in 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:

1. There should be a consistent and repeatable build/linking process for all OpenGL applications.
2. 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.