Sculpting with the Multiresolution Modifier in Blender
Creating a multires mesh in Blender is just like adding any other modifier to a mesh object. The figure shows what the Multiresolution modifier block looks like.
The Multiresolution modifier is similar in appearance to the Subdivision Surface modifier. By default, the Multiresolution modifier starts with zero subdivisions on your mesh. Use the Subdivide button to increase the level of subdivision that you want to add to your mesh. Subdividing increments the values for Preview, Sculpt, and Render. Like the View and Render values in the Subdivision Surface modifier, these values control how many levels of subdivision you see in the 3D View, both while sculpting and when your model is rendered, respectively.
However, unlike with the Subdivision Surface modifier, you don’t have exactly six levels of subdivision to switch between. In the Multiresolution modifier, the number can be as low as zero and as high as your computer’s processor and memory can handle. And before adding a level, you have the option of choosing Catmull-Clark Subdivision or Simple Subdivision, like you can with the Subdivision Surface modifier.
The only caveat is that you can’t freely change between subdivision types on a given level with the Multiresolution modifier. Changing from Catmull-Clark to Simple (or vice versa) has an effect on all multires levels.
If you have a Subdivision Surface modifier on your mesh, I recommend applying it to your mesh or removing it from the modifier stack before adding the Multiresolution modifier. Because the Multiresolution modifier uses the same process to create subdivision levels, you really don’t need to have both active at the same time.
After you have a level added, you have some additional options available. Clicking Delete Higher removes all subdivision levels greater than the level you’re currently in. So if you have five levels of subdivision and you’re at level 3, clicking Delete Higher effectively kills levels 4 and 5.
Enabling the Optimal Draw check box does the same thing that the corresponding check box does in the Subdivision Surface modifier: It prevents Blender from showing subdivided edges in the 3D View.
Some 3D modelers who use sculpting tools like to overlay the model’s wireframe on the mesh (Object Properties→Display→Wire check box) as they work so that they can have an idea of how their topology looks. Without Optimal Draw enabled, the 3D View of your model can quickly get cluttered, so enabling this check box simplifies the display for you.
Now, if you try to tab into Edit mode on a multires mesh, you still see only the vertices available to you in the cage provided by the base mesh. So how do you actually edit all those additional vertices created by the Multiresolution modifier?
The answer: Sculpt mode. Sculpt mode treats your mesh very much like a solid piece of clay. You have a variety of sculpt brushes that help you shape and form your mesh to look exactly how you want. You can activate Sculpt mode from the Mode menu in the 3D View’s header.
Alternatively, if you have the Pie Menus add-on enabled, Sculpt mode is a menu item you can choose when you press Tab. When you’re in Sculpt mode, the Tools tab of the Tool Shelf (T) updates to show a whole set of options available to you for editing your mesh.
If you have a drawing tablet like the ones manufactured by Wacom, Sculpt mode takes advantage of the pressure sensitivity that a tablet offers.
When working in Sculpt mode and using the Multiresolution modifier, the general workflow is to start at low levels of subdivision to block out the rough shape of your model and then proceed to higher levels of subdivision for more detailed elements of your model.
The process is very much like traditional sculpting in meatspace, as well as box modeling in the CG world. The only difference in this case is that the Multiresolution modifier allows you to freely move between high and low levels of subdivision, so you don’t have to block out your whole model in a single go.
Nothing says that you’re required to use the Multiresolution modifier when sculpting in Blender. In fact, Sculpt mode works just fine without any Multiresolution modifier at all.