Introduction to Maya Interactive Groom [2/5] (Patreon)

Note on Formatting

Throughout these articles I'll highlight the first occurrence of important new terms in bold and parameter/tool names in italic.

Getting Started with Interactive Groom

First, download the attached head model. It has UVs and the mesh density is good for when we use Houdini later. Of course you can also follow along with any other suitable model.

Import the mesh into Maya and switch to the Interactive Groom workspace.

Select the head mesh and click the create hair and fur icon on the XGen shelf.

Enter a custom name ("hair" in this example) and set the density to zero for now. All of these settings can and will be changed later, but you can set width scale to 0.1 as a good starting place. Click create.

If you look over at the XGen Interactive Groom Editor pane, we’ve now got what Interactive Groom (IG) calls a description. A description is a collection of parameters and tools that create a full groom.

IG works on a layer system similar to Photoshop, where each layer modifies the one below it. This system is non-destructive, meaning you can add and take away layers and retain the work you did in all the others. Say you add some frizz in a new layer and decide it doesn’t look good. Simply mute or delete that layer and all your other work remains untouched.

Click the + icons to expand the layers. The defaults that every description starts with are <name>_base, scale and sculpt.

Creating Guides

To get started making our groom, let’s create a guide modifier.

Select the new guide layer and click create in the Attribute Editor pane.

Expand the new layers and select inGuide_base. From here we’ll use the place brush and density brush to create guides.

The place brush is useful for creating a small number of guides that have unique shapes. We can use that on the top of the head.

Click the place brush button and open up the Tool Settings pane. This is where we'll be customizing every brush and tool we use. In this case, set the initial length to 5 and turn on object X symmetry. This will mirror all our placed guides on the left to right axis.

Now the fun starts! For this hairstyle we'll create a longer set of guides on top of the head. A good habit is to create a border/edge around where the longer hairs end and then fill in the empty space evenly. Don't worry if it's not quite right, there will be plenty of opportunities to refine it later.

The short hairs on the sides and back are a good task for the density brush. Go back to the Attribute Editor and click the density brush button to activate it. Open the tool settings, set the density fairly low (0.5) and simply paint over the surface of the mesh. You can set the density to zero and paint again to "erase" any misplaced guides.

You can also tidy up the edges using the place brush again. Don't forget to set the Initial Length to 1 to match the work we just did with the density brush.

After finishing you should have a budding masterpiece like this:

Now we’ll use the grab tool to shape the guides as desired.

This is a good time to introduce Maya's radial menus. Instead of jumping around to the XGen shelf and the Tool Settings pane you can access most tools and parameters by holding shift and right click, or just right click alone. Drag the mouse and release the right mouse button over the option you want. If you select the square to the right of each option you'll open the Tool Setting pane which is convenient if you want to change some brush settings first.

You’ll usually want to turn on collide with meshes. This makes life a lot easier as it's sometimes hard to line up the camera just right and as a result you end up with hairs going beneath the skin. You can customize the collision distance in the Tool Settings pane. Set the distance too far and the hairs will unnaturally "hover" above the skin, too close and you'll get some penetration regardless.

Another useful shortcut to remember is to hold down B and left mouse button and move the mouse left or right to change the size of the active brush.

Before getting to work, we need to make sure the correct sculpt layer is active. When we created the description a default sculpt modifier was initialized, as was one when we created the guides. Since we're working on the guides now we'll want to set the guide sculpt modifier to active. Do that by clicking the edit button as shown here. Also, turn off visibility on the guide layer. This will improve performance significantly.

Shift right click or use the XGen shelf and select the grab tool. Make sure collide with meshes is on and the distance is set to 0.1 or so. We can now use this to brush the guides into the position we want.

Brush the shorter guides so they face down along the skin. This is where skin collision comes in especially handy since these would all go beneath the mesh surface otherwise.

You can use the Freeze tool to isolate specific guides for fine tuning. Freeze a guide by painting over it, then select Invert Frozen Effect or Invert Frozen in the radial menu to quickly isolate a it.

Creating the Hair

Now that we’ve our guides into the general shape of our hairstyle, we can switch to the main description to fill in actual hair.

First, select the base layer in your groom (in this case, hair_base) and enable the density brush. You can select various Paint Operations in the tool settings, but let's go with Set and a Value of 50. Also, make sure the visibility on the guide layer is turned back on. Otherwise, our new hairs won't follow the guides.

Now, paint in the hairs all over the scalp. If you go over the edges just set the density value to zero and paint again to erase. You'll notice that the hairs aren't filling in the correct direction on the left side of the head. This is easily fixed by switching to the grab tool and nudging the guides a bit. This will snap the hairs into the correct position and you can continue painting.

Now we need to introduce the elements that truly make a groom look real: noise, clumps and flyaway hairs.

First, let's make the hairs a more realistic width. Select the very top level of the description and set the width scale to 0.03, taper to 1 and taper start to 0.7 as shown below. Taper start at zero means the the taper begins at the root, so in our case we're making it start closer to the tip. You can also turn off visibility on the inGuide layer to hide the yellow guide curves.

Let's add some noise. Click the add modifier button and select noise. This is already looking much more realistic at the default settings! Feel free to mess around with the sliders to get a look you like. Remember, you can always hide or delete a layer and it won't affect any of the work you've done so far. There's lots of room to experiment.

Clumping is key on any type of groom. Even with the straightest, finest hair there are always clumps. Click add modifier again and this time select clump. Obviously the defaults aren't quite going to work for us.

Let's dive in and see what some of the clump parameters do to effect the look.

Clump: 0 is no clumping, 1 is full clump and -1 is full inverse clump (the hairs are pushed outward instead of pulled together).Clump scale: this controls the shape of the clumps, from root to tip, left to right on the slider. You can click the arrow button to make the graph editor bigger and easier to control. Let's move the rightmost control point up to make the clumps less pointy.

Clump Variance: pushes hairs towards other clumps to break up the evenness.Preserve Length: 0 means the the hairs stretch to match the clump shape, 1 preserves the original length. Generally you'll want to keep this closer to zero.Randomness: 0 places the clumps evenly across the skin while higher numbers randomize their placement. You'll almost always want lots of randomness here.Density: this is a very important parameter. Densities closer to zero give you larger and larger clumps. Note that you can go above 1 here. In our case a density of 10 looks good.

These are the basic parameters you'll need to start creating nice clumping. There are many more, including many that involve painting masks, plus some advanced controls with more graph editors. We don't necessarily need any of those for our basic groom, but feel free to play around with them.

Next, let's add a new sculpt layer, activate it by clicking the edit button and modify the groom's shape outside of the broad shape defined by the guides. You can use the length tool to create some variance in the length, trimming spots and extending others. I like to use this instead of the cut tool. Set the increment to a negative number to decrease the hair's length. For very fine adjustments you can either set the strength very low, or set a small increment.

Now I'll go over the entire groom with various brushes, modifying length, freezing and unfreezing sections to work on specific parts, and brushing the hair to introduce randomness and directionality. This is where the artistry comes in, so experiment and have fun. Feel free to add as many different layers as you want. You might want a sculpt layer where you only work on the top, one for the sides, etc. Note that layer order matters. In my example here I'm sculpting on top of the clump and noise, which is going to lessen the effects of both. I want this so as to further break up the uniformity. Also note that things might slow down or behave unexpectedly if you have many layers. For example, sculpting below a clump layer might totally alter the effect of your brush strokes as the clump layer modifies in real time everything you do. In this case simply temporarily mute the problematic layers.

Last but not least, we can change the density multiplier on the base layer, as well as change the width again. Also, for the final look we can set CV count to something like 10 and click rebuild. This will smooth out any jagged hairs.

For this image I set width to 0.01 and density multiplier to 3. I also attached a default Arnold hair shader. Don't worry, we'll be getting to rendering in detail at the end of this series, stay tuned!

Exporting

One of the weaker aspects of Interactive Groom is its limited export options. You can only save out Alembic and there are really only two settings. To access the export window, select the description and go to the Export Cache menu option.

You'll always want to have Write Final Width checked so that any taper the hairs have will be included. If you did not use painted maps you can leave Multiple Transforms unchecked. If you used painted maps, however, it’s essential to check it. Otherwise, the export will be missing all the alterations made with the maps

Intermediate/Advanced Note: Using Maps

You may have noticed that most IG parameters can be controlled with painted maps, created either in Maya or in an external paint program. This is a more time-consuming method, but also gives a lot of control. Every part of the groom, including clumps, length, noise and more can be controlled with maps. A lot of the decision to use them or not comes down to how procedural you want your groom to be versus how free-form and “sculptural” you prefer.

One benefit of using maps is you have a “record” of what you did on each layer. Using only brushes broadly preserves a look, but the steps used to create that look are lost. Maps create a step by step history for your modifications that can be easily visualized and altered at any point.

Personally, I prefer the sculptural approach. It's more fun, less complicated and you can get excellent results. There is definitely a place for painted maps though. They’re not too difficult to use and give you a ton of valuable control. I'll cover maps in more detail in an appendix to this series.

Closing Words

Congrats! We made a complete basic groom from start to finish using a wide range of Interactive Groom tools. This should give you a great foundation so you can practice and experiment freely.

Up next, Houdini!