Install this version:
emerge -a =dev-games/netradiant-gamepacks-1.5.0.20200419
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask =dev-games/netradiant-gamepacks-1.5.0.20200419
Or alternatively:
emerge --autounmask-write -a =dev-games/netradiant-gamepacks-1.5.0.20200419
# Copyright 2020 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
EAPI=7
MY_PV=$(ver_rs 3 -)
DESCRIPTION="Gamepacks for NetRadiant editor"
HOMEPAGE="https://netradiant.gitlab.io/"
SRC_URI="https://dl.illwieckz.net/b/netradiant/build/preversions/netradiant_${MY_PV}-illwieckz-linux-amd64.tar.xz"
LICENSE="GPL-2+"
SLOT="0"
KEYWORDS="~amd64 ~x86"
S="${WORKDIR}/netradiant_${MY_PV}-illwieckz-linux-amd64"
src_install() {
insinto /usr/share/netradiant/gamepacks
doins -r gamepacks/*
}