VFX & Animation

Blender 30/30 Day 09: The Basics of Grass

james

After posting Dandelions the other day, I was asked by someone whether I knew of any better ways to make grass. I did not.

Today, however, I spent some time playing around with the hair simulator trying to get a half-decent grass effect. The intention of today is less a lovely render, and more a basic guide to making your own grass!

Step 01: Make your ground

I used the sculpt tool to create a quick ground. If you’re new to sculpting, a handy tool is ‘Dynotopo’, which increases the detail of your sculpt as you zoom further in.

Steps

  1. Create a plane, Scale it to desired size (I use 10x), and apply the scale
    (applying the scale is crucial for sculpting or you’ll get weird results)
  2. Sculpt some landscape (I use the Clay brush and the Sculpt brush)

Walkthrough:

Step 02: A single blade of grass

The simplest way I could think of to create some grass is to modify a plane.

Steps

  1. Create a new plane. Go into Edit Mode, rotate the plane by 90 around X
  2. Scale in on the X axis
  3. Extrude the top edge a few times. On the final extrusion, scale the resulting edge by Zero, which  should merge the two vertices. Click ‘Remove Doubles’ in the tool shelf to join the vertices
  4. Add some offset to each edge along you blade. You can to this individually or turn on proportional editing and move only the top vertex
  5. Add a material to you blade, and colour it accordingly (I chose green because, well, grass)

Walkthrough:

Step 03: Create a basic hair system

This step involves adding a hair modifier to your ground, so as to repeat the single blade of grass many times.

Steps

  1. Before starting on the hair, I moved my single blade onto a different layer. It helps keep things clean but is not entirely necessary
  2. Select you ground object and under the properties panel go to the Add Modifiers tab (it’s the one that looks like a snapper/wrench)
  3. Click ‘Add Modifier’ > Simulate > Particle System
  4. A new tab should have appeared in the properties panel, that looks like a collection of stars. Open that tab
  5. Under Type choose Hair, and be sure to check Advanced
    [Some of the drop-down categories are open by default. I like to close them all first so that all the options seem less overwhelming]
  6. The three categories to pay attention to at this stage are: Emission, Rotation, and Render.
    1. Emission: Deals with the number and distribution of particles. A higher Number means more dense grass. [Note] I had an issue with LOW POLY terrain where I also had to increase the ‘Particles/Face‘ setting as by default all the particles were emerging from the center of each polygon.
    2. Rotation: How are your particles rotated? ‘Initial Orientation’ determines which way your particles point, and Phase determines how rotated around that axis they are. If you want a random rotation for each particle (which makes grass look a lot better) increase Random as well.
    3. Render: Here change the render type from Path to Object, and choose your single blade object. You may need to increase the size to your liking, and you have the option to add random size as well (more on sizing later). Once you have selected your object to duplicate, it is possible that its rotation is a bit messed up. Follow steps below to resolve
    4. Fixing grass rotation: If your grass is rotated incorrectly you’ll need to re-orient the original mesh. You can do this a few ways, but I suggest:
      1. Select you single blade object.
      2. SHFT + C > Cursor to selected (This should place the cursor at the bottom of the blade
      3. Change Pivot Mode to ‘3D Cursor’ (Full Stop on keyboard)
      4. Enter Edit Mode and select the whole mesh (‘A’)
      5. Rotate around the required axis (if you’ve followed me here it’s -90 around X)

Walkthrough:

Step 04: Choosing where your grass goes

Since by default the hair is distributed even across your emitter object (the ground), and since nature does not really do anything ‘evenly’, we need a way to tell the particle system what areas to prioritise and what areas to ignore. This could be done with a noise texture, but I prefer the Weight Paint tool as it allows us a lot more control over our distribution.

Steps

  1. Select your ground object, and from the object interaction menu (at the bottom of the 3D window- where the Object and Edit mode buttons are) choose ‘Weight Paint’
  2. In the properties panel, under the Mesh Data tab, add a new entry under ‘Vertex Groups’
  3. With your new group selected, paint onto your ground mesh where you would like grass. Play around with the brushes and settings available, though I use Add and Subtract most often. The important thing to note is that Blue describes areas of NO INFLUENCE and red describes areas of the MOST INFLUENCE, with a gradient in between.
  4. Once you have your grass area all painted up, switch back over into the Particles tab and under the Vertex Group category > Density, add your vertex group you just painted.
  5. Repeat for Length category if desired, which will change the grass length based on a vertex group (i.e. blue areas will be shorter than red areas)

Walkthrough:

Step 05: Selling it

Now that you have the basic workflow down, you can use these steps with different variations to make more compelling grass. Try to increase the complexity of the ‘single blade’ mesh, to bulk out your grass a bit. Since the scene is so busy anyway a few repeat patterns should go unnoticed. In addition, the ground object can have as many particle systems attached as you’d like, which mean you can create many different varieties/species of grass & plants. Using weight painting you can scatter those variations around your scene with different densities.

What I did:

In conclusion, the grass doesn’t always have to be greener on the other side. Make your own damn grass.