Inside of a shader how can I convert a world direction relevant to a vertex's local position

I’m trying to make a shader for my grass that will allow me to have all the grass blowing in the same direction regardless of its rotation.

This is what I have at the moment (

My problem is that I want my grass to blow in the world direction (0, 0, 1), but the vertex offset input is for the vertex’s local position. I need a way to make my world direction relevant to the vertex’s local position.

Any input/help is appreciated.

I ended up solving my problem with help from someone in the IRC channel.

If anyone stumbles upon this in the future with a similar problem you need to multiply your world direction by _Object2World.