Making Realistic Grass with Cinema 4D (with a little help from Mograph and Hair), third part
20.2.2008· Autor: Matúš Laco·
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In this portion of the tutorial, we´ll stay completely within the hair module to make our shorter grass. After working through the tutorial, you should know how to make grass, but even more, you´ll understand the workings of the hair module. And let´s get one thing out right from the start-everything in the hair module is scale-dependent. That is, if you have to rescale your scene later, you´ll also have to dive down into your Hair settings and change quite a few things. So as with so many things in 3D, planning in advance is of prime importance.
For example, if you change your Hair length, you must change other things also. Thickness must change, along with the variation parameters, as mush Clump, Cloning Hair settings-basically anything that is measured in absolute units (millimeters, inches, etc.). By all means, keep this in mind.
So, on to our grass! To get started open the scene we've been creating and select the terrain object. Double-red the tall grass you made last lesson. Make a new Hair object. This new Hair is too long by default, so go into the Guides tab and make the Length 40 units. Taking a peak with a test render, you'll see we have a few things to change.
First let's raise our count-make it 60,000. In the Hair material, go to the Density channel and add a noise channel. Make the noise type 'Turbulence,' with global size to 180% and low clip / high clip levels at 42% and 63% respectively. Finally set it to UV 2D space. We do this because the Hair object and shader support UV coordinates. Using this noise has the effect of masking our hair's density, something like using an alpha channel. Do a test render, if you're not already: it's good to keep track.
Now let's change the shape of the grass shoots. Go to the Thickness channel and change both size values to 0.3 and the variation values to .03-.06, using the curve settings to adjust the shape.
Our shoots are too straight, so let's go to the Hair object's Frizz channel. Set the Frizz value to 50%, variation settings to 10%, scale x to 100% and scale y to 50%. These settings are very important as they apply to all hair instances. As in the image, use the curve settings to fine-tune your settings.
A little update in Kink channel
When used as animal or human hair, hair often clumps; thus the Clump settings in the C4D Hair material. In this case, we're going to use this setting to repel hairs from one another, and the result will be a more random distribution for our grass. We do this by going to the Clump settings and putting a negative number (-20 in this case) into the clump parameter there, with radius set roughly to 15-30 (play with this as you like), and of course we're going to adjust the curve, pulling the first point of the top spline so that it goes low to high. Now when you render, things are much improved, eh?
If you study greass you'll see that many of the grass shoots bend downard, into the ground. This behavior is best approximated in the Bend channel of the Hair material. Make the axis be global and the direction +Y, then set the strength parameter to 30%, variation to 10% and amount to 50% (so that 50% of our instances have this setting).
Now, another thing about grass is that it's patchy, and the grass on the edges of the patches is sometimes shorter. Amazingly enough the C4D Hair module allows us to simulate this behavior also, and it's as simple as going to the Density channel and copying the noise there and pasting it into the Length channel. It's another mask, with the gray areas between the dark and light providing for 'falloff' in our grass length at the edges of the areas of lower grass density (i.e., the patchy areas).
So there we are! Our grass looks quite real, though for reasons of demonstration I did a bit more tweaking. First, I went to the Tighten channel and set tighten to 18 degrees, with 40% as the amount (so that it affects 40% of our instances). Adjust the curve to match the image.
Lastly, let's go to the Kink channel and set kink to 6% and variation to 6% also, with direction settings at 30 for both x and y, and don't forget to match the curve in the image provided.
At this point, we have lovely, scraggly, short grass that renders with admirable speed. We're at the end of part three of what was originally intended to be a three-part series, but for reasons of length, I think it best to break this third part in two. Thus, next week we'll put the wrapper on our project by doing our grass surface settings and lighting. And then, we're done! Good luck planting your grass. Maxon has provided the best seeds you'll find anywhere.