Ultimate Mental Ray Grass Shader!

I'd been wanting to do this for some time now. I wanted to create a grass shader that would work for every situation. Whether the camera was 500' or 5' from the ground the grass would look good.

mental ray grass shader

There were alot of factors I wanted to consider when creating this shader. When the camera was far away from the grass I didn't want it to look like repeated tiles of the same grass map. Rather I wanted it to have that random field look, as if you were in a plane looking down of the world. So I created an image map from an aerial photograph of what grass would look like from 500' in the air. From this distance I also knew that having displacement on the grass would be useless from so far away, so I put a falloff in the displacement slot based on distance. So at this distance, displacement wasn't even calculated.








When the camera came closer to the grass, then it would displace the shader. The close up grass also uses a different grass map from the far away grass. For the far away and close up grass, both of them also have a falloff that simulates atmosphere or grass blades on the horizon. So as the grass gets further from the camera the color fades out and gets lighter.












You could use this for v-ray as well, but it's really optimized for mental ray with the mr photographic exposure control (the reason the maps in the output are so dark). I put together a diagram that shows how exactly I created this shader if you're curious.

Here is the max file (max 2008) with the grass shader.