Basic Mechanics

Scultiping within a 3d space has multiple uses. Sculpting tools (especially when coupled with a digital drawing tablet) make the creation of organic objects much easier. It's also easier to add fine details across wide areas since in most programs you can literally "paint" a color and a surface depth (such as bumps and wrinkles) at the same time.

Keep in mind that you typically would NOT use the high-poly sculpted mesh for anything. High poly sculpts can be made up of millions of polygons and put too much weight on a processor to be used in real time graphics so they are not ideal for video games or to manipulate in real time with 3d packages like Max or Maya. What we generally want is to use the high poly sculpt to make a special texture map that can mimic the details of the high poly on top of the low poly.

For a more in depth explanation of Normal or Displacement maps, see the "Texture Types "section.

There are two basic approaches to sculpting in 3d, starting from a low poly mesh and moving to a higher, or starting from the high poly mesh and moving to a lower.

Let's quickly outline the steps involved with both.

Our first option would be to start with a low poly model.

  1. Create a low poly model (which also serves as the model to be used in our game / animation).
  2. Modify the low poly to a "Medium Poly" to allow smoothing and cutting. This is what will be imported to our sculpting program.
  3. Use our medium poly version to start sculpting the high poly version (keeping the final shape as close to the original as can be).
  4. Bake any required texture maps.

Alternately we can start with the high-poly model.

  1. Sculpt a high poly organic model. When starting here we can do concept modeling as well, keeping the version we want.
  2. Retopologize the model to a low-poly version (most of the time we will be using the manual process).
  3. Combine with high poly versions of any synthetic / mechanical looking pieces that might be needed.
  4. Bake any required texture maps.

It's only after either of these methods are through that we'd move on to baking a texture map from them.

In reality a mix of the two is probably best. Sculpting is generally more useful for organic objects and less so for synthetic objects. That means that you not want to "finish" the model as a low poly version first but making any parts that involve hard edges or flat surfaces can be made first, and then have more organic pieces added to them seperately.

Low to high process

Starting with a low poly mesh for a model can be a good thing in that you sometimes may not even know if a model will need a high-detail map. Sometimes a model that is especially small or perhaps one seen from a distance simply would not benefit from having a normal or displacement map. But if we find that we do need one,

1. Make the low poly mesh

The first step is as simple as making any model.

Be warned that if you know for sure that a model is going to be sculpted into a high poly version then you may want to forego the texture mapping process at this point. It's not impossible, but sometimes during the sculpting process you can find ways that you want to change the model in, any maybe even use the low poly modified by your sculpting software to better match the final high poly sculpt.

2. Modify it to a "medium" poly mesh

There are a few basic changes you'll apply to this low poly mesh to help ready it for sculpting.

Add cuts to retain hard edges

Often times one of the first actions you'll take on a new sculpt is to sub-divide the surface to both add smoothness and polys that can be sculpted with. But if you apply this directly to your low poly model then chances are you'll be softening corners and edges that you want to be sharp.

You might be thinking it's possible to subdivide the object without smoothing in your sculpting program and work from there, and it is, but this will also harden the polygons in curved surfaces you otherwise want to be smooth. The following image illustrates these problems.

This image shows two meshes and what they look like when a mesh smooth modifier/attribute has been added. The far left is our original mesh of a simple torus which will usually be the same as our low poly model. Once mesh smoothed it no longer resembles the original hard edged tube but a smooth torus. This is obviously not what we want.

The second pair, on the right, shows the same mesh after having been subdivided *without* smoothing. As you can see we're not smoothing it as much anymore, but because the added edges are helping to retain the shape of the original the harder edges around the sides are becoming more obvious. These edges would be visible in a detail map which would also be bad.

Here we have another pair of meshes and their smoothed versions.

With the first mesh we've taken our original tube and tried to cut extra loops manually along the edges to cut down on the hard edges of the smooth version. In this case we did not think about the direction of the cuts and ended up with a result no different then the previous subdivided model.

Lastly we have the version we want. In the final mesh pair we've *ONLY* cut along the corners we want to retain sharpness on. By not cutting along the radial edges we've allowed the smoothing modifier to still smoooth the actual curve of the shape.

This is the result we want.

Adding cuts for good sculpting flow.

We shouldn't get ahead of ourselves but it's important to know that when sculpting it is always best to have the quads of a mesh be more square than rectangular. If you are getting what could be described as "stretching" or some kind of "blurring" in your sculpting strokes then it may be because there were too many rectangular polys. More quads will help alleviate any future blurring as seen in the image below.

Note how the plane on the left has been subdivided to have square polygons while the right has rectangular polygons (both shapes have the same polycount). The rectangular polygons are not allowing good "resolution" to sculpt from, and therefore are "blurring" the sculpted stroke in one direction more than another.

Seperating polygons

To make absolutely sure we get hard creases where we want them we may also want to completely disconnect some groups of polygons from others. This will completely prevent the smoothing algorithm in our sculpting program from being able to smooth the otherwise connected geometry.

We'll just need to be carefuly that the seams of these edges are not torn apart (programs like ZBrush have options to make open edges immoble for this very reason).

Seperating Pieces

Another thing we'll want to do is ask ourselves if we should the object into seperate pieces, even if the object is meant to be a continuous substance. We need to do this because the nature of sculpting, where we push and pull on surfaces that may recede into one another, can easily cause overlapping that will make the mesh hard to work with.

This will be especially true of pieces like eyeballs, teeth, and horns, etc.

It will also help greatly when it comes time to baking a texture as baking individual pieces will always give better results.

3. Sculpt the high poly mesh

The benefit of the medium poly can now be seen when we import the model to our sculpting program. Here is an example of a full model with and without the previous suggestions applied.

High to low process

Starting with a high poly sculpt for a model has its benefits. It can be easier to experiment with different shapes since you aren't working on the "final" model. It also allows for a more sketch-like style. Since most sculpting is done with a drawing tablet instead of a mouse the basic, quick actions of sketching a shape can greatly help visualize an idea.

To Retopologize a model is to change the layout of points and edges while retaining the original shape as much as possible.

Once you are happy with the sculpt of your model and are fairly sure the general shape of it will not change then you can start the process or retopologizing it.

Manual Retopology

Many sculpting programs have automatic retopology tools which have very good uses (outlined in the next section) but the creation of useable low poly meshes is not yet one of them.

The actual tools used will differ *greatly* between programs but the basic idea will always be the same. You want to create a new mesh that adheres to the shape of your sculpt but also has good mesh flow. It's almost like tracing an image but in 3d. And should be fairly straight forward.

  1. Find the add point tool.
  2. Find and turn on snapping to a *surface*, and in a 3D mode, not a 2D vertex, edge, or polygon snapping.
  3. Spend a stupid amount of time making the new mesh on top of the surface of the old.

See the program specific pages for a more step-by-step process.

Sculpting techniques

The first thing to do when sculpting in high-resolution meshes is change the way you think about modeling.

With low poly modeling you often start with a primitive shape that is similar to your inteded object shape. In that case the same vertices and polygons you start with are often found in the final model. With high poly modeling you sohuld not even be worrying aboout individual points or polys. Think only of the surface shape and texture.

"Sculpt & Smooth"

In nearly every major sculpting application the SHIFT key will be a shortcut for smoothing the surface of an object. Take advantage of this. Don't think that because it is called smoothing means it is only going to be used on smooth surfaces. It is very useful for helping to form the general shape even before you get to defining the texture of the surface. Here are the two main situations you'll use it.

The first case is easy to grasp. We use words like "push" and "pull" to describe sculpting but you can also think of it as "building up" and "removing" volume from a shape as if you were working with clay or some other modeling compound.

In the case of the to the right we need to build up a bulge. To make the bulge a smooth, continuous shape, it will be as simple as 1. swiping a "sculpt" brush back and forth, and then 2. holding down SHIFT while swiping over the same area until the surface is smooth.

We've now built up more volume which can be further sculpted into our desired shape.

The second widest use of the smoothing tool will be to help make shelfs or extusions that don't fall off on all sides. Look at the accompyning series of images. In this case we are sculpting a donut with frosting/glaze on top.

The result we want here is to have a drop off from the frosting to the dough. The problem is that when you use a sculpting brush the default shape of it is probably a bell-shape which has falloff on all sides. In this case not only did we not worry about the falloff being on both sides but we lowered the falloff to have an even sharper edge.

We do that so that we can allow the lower side of the sculpted line to define the end (the underside) of the frosting. We then simply apply smoothing to the top side to give the appearance of a constant surface.

...and then we have a simple donut shape. This basic two step approach can be used for everything such as facial features (lips, eyelids) to detailing on more hard-surface objects such as car bodies.

Automatic Retopology

Retopologizing a model with a quick, automatic algorithm is a useful process for a few reasons.

The natural pushing and pulling of points that happens during sculpting often distorts the starting mesh into skewed polygons. Retopology operations allow you to re-establish a quad-heavy mesh for further modeling.

Let's look at an example.

Here we have a human face that we wanted to make more cartoonish, so we began to overemphasize some features like the length of the nose. As you can see the act of extending the nose out from the face (which started as a primitive object) has left some of the polygons in the nose distorted and rectangular. By themselves they look ok. But what happens when we get to our detailing stage? What if we want to add a nice round wart to it?

Smaller details like this suddenly become distorted because of the same problem discussed before. The stretched mesh is no longer dense enough to mold into finer details and obvious aliasing of the edges occurs.

So we run a retopology function (notice the change in the wireframe to the right). The process will be different across programs but the effect remains the same. Once done we would ideally have a mesh that has more uniformly shaped polygons (closer to square) which are more conductive to adding detail. As you can see in the face model here the wart we added no longer has the obvious aliasing around the edges. It's now a much smoother, more circular, and overall realistic wart and we are free to subdivide further to add even more detail if we choose to.

When using a retopology function there are a few things to watch out for. You will probably get an option for "target" polys. As with most functions it might be best to leave things at their default settings but in this case you can increase the number to your original count if the new mesh does not seem to capture the details of the original mesh. If raised however, never go too far above the original polygon count.

Another thing to note is that the original model on the left has a polygon count of 686,080 while the retopologized version has a count of 230,144. So if your are careful enough then not only can you end up with a model that has better mesh density distribution, but a model that has fewer polys, which should make your real time rendering smoother as well.

Baking textures

This section is better covered by the program-specific sub pages, but no matter what program you use there are some things you may want to take into account.

  • Watch your normals. Many baking algorithms take the normal smoothing of a model into account. If what you know should be a flat surface is appearing slightly curved or fades from light to dark tones slightly then you may want to double check your export settings. Most programs will have an "export with normals" or similar option during export that you can try toggling. If that fails, something as simple as trying a different file format might help, .obj instead of .fbx for instance.
  • Remember that not all baked in details have to represent the original mesh. What do I mean by that? Take for instance the model below of a simple cuboid object with screws baked into the texture. In the original high poly version of this object we don't actually have the screws as part of the high poly mesh. They are in fact floating *above* the mesh.

Misc. Tools

tbd

An online sculpting tool. Be advised this tool is, currently, more suitable for quick practice sculpts than for creating finalized assets. It involves a simple round sculpting brush and uses no decals, textures, layers or other high-end tools and options. https://labs.sketchfab.com/sculptfab/