This is stated in Wayland docs and mpv configure script.
Package-Manager: portage-2.2.24
v4l? ( || ( alsa oss ) )
vaapi? ( X )
vdpau? ( X )
- wayland? ( opengl )
+ wayland? ( egl )
xinerama? ( X )
xscreensaver? ( X )
xv? ( X )
$(use_enable X xrandr)
$(usex X "$(use_enable opengl gl-x11)" '--disable-gl-x11')
$(use_enable egl egl-x11)
- $(usex wayland "$(use_enable opengl gl-wayland)" '--disable-gl-wayland')
+ $(use_enable wayland gl-wayland)
$(use_enable opengl gl)
$(use_enable vdpau)
$(usex vdpau "$(use_enable opengl vdpau-gl-x11)" '--disable-vdpau-gl-x11')