Howto: Automatically run minecraft on the dedicated GPU

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Running Minecraft on the dedicated GPU requires launching the internal java command with primusrun prefixed to it. (this command may depend on your setup, alternatives include optirun, nvidia-offload or prime-offload).

Just running primusrun minecraft-client doesn’t seem to work.

It is possible to get this working by setting a custom java runtime command inside the minecraft client, but it requires hard-linking to the package, which is a bit annoying to set-up and maintain.

Instead of doing that I have created an overlay for the Minecraft Package in which I switch out the java runtime and wrap the java command with one that executes the required script first.

This is what I have come up with:

  primecraft = pkgs.minecraft.override rec {
    jre = pkgs.jre.overrideAttrs (old@{installPhase ? "", ...}: {
      nativeBuildInputs = old.nativeBuildInputs ++ [ pkgs.makeWrapper pkgs.primus ];
      installPhase = installPhase + ''
        mv $out/bin/java $out/bin/.java-wrapped
        echo "#! ${pkgs.bash}/bin/bash" >> $out/bin/java
        echo "script_dir=\$(dirname \$(readlink --canonicalize-existing \$0))" >> $out/bin/java
        echo "export vblank_mode=0" >> $out/bin/java
        echo 'primusrun $script_dir/.java-wrapped "$@"' >> $out/bin/java
        chmod +x $out/bin/java
      '';
    });
  };

This currently requires rebuilding the entire java runtime which takes quite a bit of time. Luckily I have a build machine so I don’t really need to worry about that. That being said, it’s still not ideal but the only solution I can think of would require copying the entire package to a new one and I am not sure how to do that properly.

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