Creating Grass with Mograph and Vray

Here is the development of the grass patch (seen from a rather great distance) inside Vray. The rendering times had to stay below 5-7 minutes per frame, using GI.

(click on image to see the WIP animation)

Here are some remarks:

• Visibility tag for distribution of the grass to set to boxes. I needed a LARGE number of instances for this sphere (approx 15000)
• General orientation of the grass should be upwards - I used a target effector but weighted it lower than 100% to get direction - as last effector in the list.
• 2-sided materials in Vray made the render considerably slower (factor approx 2-3) and at this distance translucence doesnt matter much.
• Other cloners to redistribute variations and single plants.

Next step would be SurfaceSPREAD plugin, but I didn't have it at this time.

The visibility tag and mograph

For scenes with a very large number of cloned objects I have used the visibility tag, to specifically control the number of clones visible on screen, mainly because my graphics card is rather old.

Unfortunately, the detail in visibility can not be switched off for rendering. This means, that it has to be switched off manually before rendering.

In combination with the "Render Instances" option in the Cloner object the behavior is slightly harder to predict.

Thoughts about motion blur

Below is a shot that shows all the potential problems I can have with motion blur. This is a parallel camera motion to the movement of the white ball, which itself is moving at fast speed across the table.

This particular frame was rendered with the physical renderer. Unfortunately, there is no postpro control on the motion blur, and the frame took 30 minutes to render - highly impractical.

Watch the area, where the two balls overlap - I think that the physical renderer doesn't get it right, but I'm not 100% sure, how the motion blur phenomenon would work on a real cam in this case.

So, we have at least three different objects moving at different speeds

• the white ball (strong movement)
• the other balls (motion blur through camera)
• the table texture with different motion blurs depending on distance from camera.

So I am left with the following solutions to get a good motion blur:

• High importance: physical renderer and go to a render farm
• Pro: perfect(?) motion blur, physical accuracy
• Contra: Problem with setting up the other passes (more research needed)
• Low importance: plugin in AE 
• Pro: adjustable in post, might catch the above problem
• Contra: Doesn't look perfect, complicated object buffer handling, more overhead