# FindOpenGL

FindModule for OpenGL and GLU.

## Optional COMPONENTS

This module respects several optional COMPONENTS: `EGL`, `GLX`, and `OpenGL`. There are corresponding import targets for each of these flags.

## IMPORTED Targets

This module defines the `IMPORTED` targets:

`OpenGL::GL`
  Defined to the platform-specific OpenGL libraries if the system has OpenGL.
`OpenGL::OpenGL`
  Defined to libOpenGL if the system is GLVND-based. `OpenGL::GL`
`OpenGL::GLU`
  Defined if the system has GLU.
`OpenGL::GLX`
  Defined if the system has GLX.
`OpenGL::EGL`
  Defined if the system has EGL.

## Result Variables

This module sets the following variables:

`OPENGL_FOUND`
  True, if the system has OpenGL and all components are found.
`OPENGL_XMESA_FOUND`
  True, if the system has XMESA.
`OPENGL_GLU_FOUND`
  True, if the system has GLU.
`OpenGL_OpenGL_FOUND`
  True, if the system has an OpenGL library.
`OpenGL_GLX_FOUND`
  True, if the system has GLX.
`OpenGL_EGL_FOUND`
  True, if the system has EGL.
`OPENGL_INCLUDE_DIR`
  Path to the OpenGL include directory.
`OPENGL_EGL_INCLUDE_DIRS`
  Path to the EGL include directory.
`OPENGL_LIBRARIES`
  Paths to the OpenGL library, windowing system libraries, and GLU libraries. On Linux, this assumes GLX and is never correct for EGL-based targets. Clients are encouraged to use the `OpenGL::*` import targets instead.

## Cache variables

The following cache variables may also be set:

`OPENGL_egl_LIBRARY`
  Path to the EGL library.
`OPENGL_glu_LIBRARY`
  Path to the GLU library.
`OPENGL_glx_LIBRARY`
  Path to the GLVND ‘GLX’ library.
`OPENGL_opengl_LIBRARY`
  Path to the GLVND ‘OpenGL’ library
`OPENGL_gl_LIBRARY`
  Path to the OpenGL library. New code should prefer the `OpenGL::*` import targets.

## Linux-specific

Some Linux systems utilize GLVND as a new ABI for OpenGL. GLVND separates context libraries from OpenGL itself; OpenGL lives in “libOpenGL”, and contexts are defined in “libGLX” or “libEGL”. GLVND is currently the only way to get OpenGL 3+ functionality via EGL in a manner portable across vendors. Projects may use GLVND explicitly with target `OpenGL::OpenGL` and either `OpenGL::GLX` or `OpenGL::EGL`.

Projects may use the `OpenGL::GL` target (or `OPENGL_LIBRARIES` variable) to use legacy GL interfaces. These will use the legacy GL library located by `OPENGL_gl_LIBRARY`, if available. If `OPENGL_gl_LIBRARY` is empty or not found and GLVND is available, the `OpenGL::GL` target will use GLVND `OpenGL::OpenGL` and `OpenGL::GLX` (and the `OPENGL_LIBRARIES` variable will use the corresponding libraries). Thus, for non-EGL-based Linux targets, the `OpenGL::GL` target is most portable.

A `OpenGL_GL_PREFERENCE` variable may be set to specify the preferred way to provide legacy GL interfaces in case multiple choices are available. The value may be one of:

`GLVND`
  If the GLVND OpenGL and GLX libraries are available, prefer them. This forces `OPENGL_gl_LIBRARY` to be empty. This is the default if components were requested (since components correspond to GLVND libraries).
`LEGACY`
  Prefer to use the legacy libGL library, if available. This is the default if no components were requested.

For EGL targets the client must rely on GLVND support on the user’s system. Linking should use the `OpenGL::OpenGL OpenGL::EGL` targets. Using GLES* libraries is theoretically possible in place of `OpenGL::OpenGL`, but this module does not currently support that; contributions welcome.

`OPENGL_egl_LIBRARY` and `OPENGL_EGL_INCLUDE_DIRS` are defined in the case of GLVND. For non-GLVND Linux and other systems these are left undefined.

## macOS-Specific

On OSX FindOpenGL defaults to using the framework version of OpenGL. People will have to change the cache values of OPENGL_glu_LIBRARY and OPENGL_gl_LIBRARY to use OpenGL with X11 on OSX.