Chapter 3
Sculpting and Retopo Workflow
The method of modeling known as 3D sculpting has recently become increasingly popular as a way to create highly realistic, detailed models. In 3D sculpting, the 3D object is handled in a way that is closely analogous to actual clay. Blender has a powerful set of sculpting features that include multiresolution mesh modeling and a variety of tools that enable highly detailed direct manipulations of meshes. More than this, Blender offers the ability to use these detailed sculpted models as the basis of new models with corrected geometry. By means of Blender’s remake topology (retopo) and normal map-baking features, you can create low-poly models with correct edge loop geometry that exhibit the same fine detail as your sculpted models.
In this chapter, you will learn to
- Get the most out of Blender’s sculpting functionality
- Use retopo to convert a sculpted form into a polygon model with correct edge loop geometry
- Use normal map baking to capture finely sculpted detail for use on a low-poly model
Sculpting with Blender
3D sculpting is a method of manipulating the shape of 3D objects in a direct and intuitive way that is loosely analogous to the way a sculptor works with clay in the real world. It is an excellent way to model detailed organic forms, and many artists find it to be a much more natural way to model than the direct manipulation of vertices and polygons used in more traditional 3D mesh modeling. For this reason, 3D sculpting is rapidly growing in popularity in the professional computer graphics (CG) modeling world.
Among the modeling options available in Blender is a powerful set of features that enable you to perform 3D sculpting on Mesh objects. Although Blender’s sculpting functionality lacks some of the versatility of the highest-end commercial sculpting systems, it is more than adequate for many sculpting tasks. In addition to the obvious advantage of being a free and open-source product, Blender’s sculpting functionality also has the advantage of being seamlessly integrated with Blender’s other modeling, texturing, and animation tools, making for a very smooth workflow.
Multiresolution Modeling
The cornerstone of the sculpting functionality in Blender is the ability to handle multiresolution mesh modeling. Multiresolution (or multires) meshes are meshes for which information is stored at more than one level of subdivision. At each level of subdivision, actual vertex data is maintained, so each multires level represents a mesh of the same overall shape as the other levels but with a different density of vertices.
In , you can see the default cube at multires levels 1, 3, 5, and 7. Vertices in multiresolution levels above 0 can be edited directly in Edit mode, and the editing changes will cascade across multires levels.
The intended way to model with multires meshes is to use the sculpting tools in Sculpt mode. You can switch between multires levels as you work, so it is possible to edit details at a high multires level and still make broader edits at a lower multires level. Edits made at each multires level will be interpolated appropriately for the other multires levels.
Hardware Requirements
Multires meshes and sculpting are areas in which the speed of your processor and the RAM you have available on your computer will come into play. A fast, recent workstation will have no problem sculpting very fine detail at a sufficiently high multires level, but an older computer or a midrange laptop may well become sluggish at lower multires levels. You will need to experiment with your own machine to see what vertex count it is able to handle easily in Sculpt mode.
In addition to a good computer, the other piece of hardware I recommend highly for the purposes of sculpting is a pen tablet input device. A pen tablet monitor is ideal because it has such an intuitive and appealing sculpting interface, but even an inexpensive USB pen tablet device is much better than a mouse for sculpting. Although the common analogy compares 3D sculpting for CG to working with clay, the actual physical process is much more similar to painting or drawing, and as such, it is something that most people are more comfortable doing with a pen device.
Another way to work with lower-end hardware is to sculpt parts of a mesh individually. Instead of working on a whole character, for instance, you could work on the head and body separately.
Sculpting Tools
When you enter Sculpt mode, several new tabs appear in the 3D viewport Tool Shelf (accessed from the 3D viewport with the T key), shown in .
Brushes
By default, the top panel on the shelf is the Brush panel, which enables you to choose the “brush” you use for sculpting. To access different brush types, you click the brush preview itself to get a preview menu, as shown in . In Sculpt mode, the first 10 brushes can also be accessed in their order with the number line. Other commonly used tools have additional hot keys, shown in parentheses in the following descriptions.
The brush types accessible in this tab are as follows:
SculptDraw SculptDraw (d) is the default sculpting tool and is very commonly used. By default, the SculptDraw tool creates an indentation away from a raised area in the direction of the 3D view. With a texture active in the Texture panel, the SculptDraw tool is used to draw the texture onto the surface of the mesh.
Smooth Smooth (s) is a crucial tool for incrementally refining your mesh as well as correcting mistakes and rough spots. The Smooth tool makes the distances and angles between vertices more uniform, effectively smoothing out inconsistencies and removing jagged areas. The Smooth tool also eliminates sculpted detail, so it should be used judiciously.
Pinch/Magnify Pinch/Magnify (p) is a necessary tool for doing detail work, in particular for creating creases or sharp ridges. The Pinch tool pulls vertices toward the center of the tool’s active area, causing the shape of the mesh to tighten around the line along which the Pinch tool is moved. If used in Magnify mode, it pulls vertices away from a central point.
Inflate/Deflate Inflate/Deflate (i) is similar to the untextured use of the Draw tool, except that the additive or subtractive change is along the normals of the mesh itself, rather than in relation to the 3D viewport. Consequently, the Inflate/Deflate tool can be used to cause the shape of the mesh to swell or to deflate or shrink the mesh along its normals.
Grab Grab (g) is a simple and useful tool. The Grab tool enables the user to manually move portions of the mesh in the Grab tool’s area of influence. Usually this tool is used to nudge portions of the mesh into shape or to shift their location slightly.
Layer Layer (l) acts as the equivalent of slapping a new layer of clay onto the shape, or, in its subtractive form, of scooping a layer of clay from the surface.
Flatten/Contrast Flatten/Contrast (f) pushes vertices toward a plane perpendicular to the view, causing the mesh to become flat in the tool’s area of influence.
Blob Blob causes spherical bumps to arise in the mesh in the place where the brush is.
Clay Clay adds volume to the mesh in a manner comparable to slapping more clay onto the surface.
Crease Crease creates sharp indentations, or creases, in a way similar to a combination of negative Draw, Smooth, and Pinch.
Fill/Deepen Fill/Deepen can be used on uneven surfaces to fill in depressed places or deepen them. This brush has no effect on even surfaces.
Nudge Nudge is similar to Grab but much more subtle. It is used to push vertices around gently, without disturbing the shape of the mesh much.
Thumb Thumb is similar to Nudge and Grab. It is a stronger force than Nudge, but it is not sustained like Grab. It gets its name from pushing clay with quick thumb movements.
Polish Polish smooths the mesh while also flattening the surface it’s applied on and reducing the volume of the mesh.
Twist Twist twists vertices on the surface of the mesh around the point where the brush touches the mesh.
Snake Hook Snake Hook pulls an extension from the surface of the mesh to follow the brush.
Scrape/Peaks Scrape/Peaks brings peaks in an uneven surface down closer to the level of the surface.
The shape of the brush’s influence is determined by the brush’s curve, shown in . The line of the curve represents the shape of the indentation or protrusion of the Draw tool. If the line goes from upper left to lower right in a convex shape, the brush’s effect is of a rounded, abrupt protrusion.
Strokes
There are several options for the stroke method used by the brush. These are set with the Stroke Method drop-down menu on the Stroke panel.
Space The Space stroke method enables you to set the spacing of brush dots based on a percentage of the size of the brush, as shown in .
Dots The Dots option is similar to Space but without the ability to set the spacing.
Airbrush Airbrush gives a brush effect that is sensitive to how you hold the brush in place. Think of the difference between holding an ordinary paintbrush in place (very little paint transfers from the brush to the surface) and holding an airbrush or spray-paint can in place (paint continues to flow onto the surface).
Drag Dot The Drag Dot option doesn’t behave much like a brush at all; it simply enables you to position a single dot of brush influence onto the surface of the mesh. The dot follows the movement of the brush until you lift the brush and then is fixed to the spot where you left it.
Anchored The Anchored option changes the behavior of the brush with respect to the movement of the pen or mouse device. With Anchored active, the point where you begin “drawing” acts as the center of the brush’s influence, and the point to which you move the pen or mouse is treated as the perimeter of the brush’s influence. The result of an Anchored brush with default curve is shown in . The arrow in that figure represents the movement of the pen or mouse device from the center of the brush’s influence to its radius.
Textures
The Texture tab, shown in , lets you define the texture that will be applied by the Draw tool. You can load a texture here and control how that texture will be mapped to the object. The Rake option causes the texture’s angle to change according to the direction of the motion of the pen or mouse device. A texture is applied to a brush in the Texture properties area by selecting the brush icon, as shown in .
None of the brushes add to or reduce the number of vertices in the mesh (although this functionality is being developed as I write this, which will significantly improve Blender’s sculpting tools). This means that it is possible to deform parts of the mesh with sculpting tools in ways that create local shortages of vertex resolution. It helps to be mindful of this when creating your base mesh, as you will see.
In the next section, you’ll look at an in-depth example of the practical use of the primary sculpting toolset.
Sculpting a Baby’s Head
The Sculpt tool is excellent for creating rough textures and uneven bumps and ridges, and for this reason, one often sees sculpted examples of demons, monsters, and old people. Unfortunately, such examples tend to leave the impression that the Sculpt tool is good only for this kind of modeling. To demonstrate that sculpting can also be effective for smooth, organic modeling, I have gone in the other direction and used a photograph of a baby as the basis of this example.
Preparing to Sculpt
Before you begin the actual sculpting process, you need to prepare your mesh and reference images. To do this, follow these steps:
1. In the window on the left, press 1 on the number pad to enter Front view.
2. In the window on the right, press 3 on the number pad to enter Side view.
3. Open the reference picture in each window by opening the 3D viewport Properties Shelf with the N key and clicking the check box by Background Images, as shown in .
4. Click Add Image and load the image from wherever you have it saved. You can find the image among the downloadable files that accompany this book in the file baby.jpg.
5. In the Axis drop-down window, choose Front view, and center the image using the X Offset value in the Background Image panel. Then switch to Side view by pressing 3 on the number pad, and click Add Image again.
6. Load the same image, but this time choose Right view, and adjust the X Offset so that the Side view of the baby lines up roughly with the cube. Your background image panels should look something like .
7. After you’ve set this up, you can split your windows as shown in .
8. Enter Edit mode and select all the vertices by pressing the A key. Press the W key to bring up the Specials menu, and select Subdivide Smooth two times. Scale the resulting subdivided mesh to approximately match the size of the head.
It is helpful to sketch out a rough shape before beginning to sculpt. Scale the whole mesh along the x-axis to fit the size of the face in Front view. In Side view, select vertices in Transparent View mode to ensure that both right and left vertices are selected, and push them around to sketch out the shape of the head, as shown in .
Because the vertex count is static for each multiresolution level during sculpting, it is a good idea to add some geometry to places that will require higher resolution to model. Since you know in advance that the baby’s ear and face will require more detail to model than the top of its head, you can make some cuts and extrusions to add vertices to these areas, as shown in and . For the ear, I used the Knife tool (K key), the Loop Cut tool (Ctrl+R) and the Smooth command (W key menu). For the face, I extruded and scaled the faces of the scale, used the Loop Cut tool, and smoothed several times.
Activating Multires
Now it is time to activate multires. Multires is a crucial function for sculpting because it enables Blender to store mesh information for a single mesh at multiple levels of subdivision. With multires activated, you can switch quickly between different levels of detail and add new levels of subdivision as they become necessary.
1. To activate multires, expand the Modifiers properties area and click Add Modifier; then choose Multires from the menu.
2. Click the Add Level button twice to create multires levels up to level 3, as shown in .
3. In Object mode, click the Smooth Shading option in the 3D viewport Tool Shelf to make the object render smoothly in the viewport. If you are using a material capture textured material as described in Chapter 2, “Working with Textures and Materials,” be sure to set the Shading option to GLSL, as shown in . Optionally, you may wish to turn off the background grid and viewport axis lines, which is also done in the Display panel of the 3D viewport Properties Shelf.
Final Preparations
You are now ready to begin sculpting. Keep an orthogonal front and side viewport visible with a Wireframe Mesh view so that you can see how your sculpt edits are affecting the overall shape of the mesh. Also, open a UV/Image editor window with your reference picture in it, so that you can refer to it directly as you work. You don’t want to get too hung up on making the mesh match the background image, because there will often be slight distortions in the photograph. Consider the background image as a helpful guide. Finally, enter Sculpt mode and bring up the Tool Shelf to have quick access to the sculpting tools. A layout I find convenient for sculpting is shown in .
The Sculpting Process
Sculpting, like painting a picture, is a gradual process that does not lend itself to rigid step-by-step instruction. This section describes the process in a roughly chronological order, but you should consider this section to be a collection of guidelines, techniques, and suggestions that will help you to get a clearer idea of how to progress rather than a strict series of instructions to follow. Take special note of the figures shown, in particular such values as brush size and strength at the various points in the sculpting process.
Roughing Out the Shapes
The SculptDraw tool is used to push or pull the mesh surface directly toward or away from the viewport view axis. This is a good brush to start with for roughing out the basic shapes of your sculpture.
1. To begin, set your brush to values like those shown in . The brush is set to Subtract, with a Radius value of 62 and a Strength value of .25. X symmetry is activated. X-axis symmetrical editing is similar in its effect to mirroring in Edit mode. In fact, the model is not perfectly symmetrical. Later, you will deactivate symmetrical editing and refine the whole sculpture.
2. With the SculptDraw brush settings as just described, begin to define the indented areas around the chin and the nose, as shown in and . You may find that different brush sizes and strengths are necessary to get the shapes right. This is normal. You will adjust your brush settings often as you progress. The important thing at this point is to maintain fairly broad strokes and to keep the brush strength weak enough that you maintain control. Note also that the brush size remains constant regardless of the size of the sculpture in the view. After you begin adjusting the view of your own sculpture, the size settings you need will change. To get a sense of the brush sizes used throughout this example, pay attention to the circle representing the brush in the figures. You can modify the size of your brush with the F key and the strength of your brush with Shift+F. Alternatively, you can increase or decrease your brush with the [ key and the ] key.
3. After you have things roughed out as well as you can at multires level 3, it is time to add another multires level and continue with the roughing. In the Multires panel, click the Add Level button and add a fourth multires level. This will enable you to sculpt in greater detail.
4. Using the SculptDraw brush in both additive (Add) and subtractive (Subtract) modes, continue to rough out the face until it looks something like . Use the additive brush to build the shape of the lips and nose and the subtractive brush to continue to shape the indentations of the chin, around the nose, and around the eyes.
5. Use the Smooth tool to go over your rough sculpt with a light pass of smoothing (no more than 0.25 strength). Then add another multires level to bring the levels up to 5. You can move up and down your multires levels with Page Up and Page Down.
Tools for Incremental Refinement
The process of sculpting is a process of incremental refinement. Let’s look at some of the tools Blender provides for this purpose.
Smooth A key element of the refinement process is the Smooth brush, which you used in the previous exercise. The Smooth brush may sometimes seem counterintuitive, because it can remove or minimize sculpt edits you have made with other brushes. Nevertheless, for the best possible results, you should use the Smooth brush frequently, often set to a low strength. Sculpt what you want, smooth it over, sculpt again, smooth again, and sculpt again until the result looks its best. Regardless of whatever tool you have active, you can always use the Smooth brush by holding Shift while LMB sculpting.
Grab Another tool for incremental refinement is the Grab tool. Use this tool to push areas of the mesh in the direction of the mouse movements. Depending on the brush size you use, this can be a very powerful tool both for adjusting large areas of the mesh and for making refinements to details. In , you can see the Grab tool used to refine the shape of the baby’s lips. Note that the arrows shown are just rough representations of the direction the tool is moving. The length of the arrows is an exaggeration. The actual tool motions for making these adjustments are much more subtle; often just a gentle nudge is enough.
Layer The Layer tool is used to add or subtract a layer of sculptable material on the surface of the object.
Additive Some artists think of using the additive Layer tool as analogous to slapping clay onto the surface of an object. However, this is slightly inaccurate. Like other sculpt tools, this tool does not alter any underlying geometry; it merely moves existing vertices, so the shape of the object is altered as though clay had been added.
Subtractive The subtractive Layer tool does the opposite. It creates an indentation of a fixed depth as though clay has been scooped out with a flat tool. The subtractive Layer tool can be very useful for marking out general indented shapes such as the eye area, as shown in . As you use this tool, continue to smooth frequently.
Using the Grease Pencil Tool for Reference Sketching
As you begin to indicate the shape of things like eyes, a problem becomes apparent. Although you have a photographic reference in the Image editor to work from by hand, it is not really straightforward to trace directly from the background image. You can sculpt in Wireframe view by entering Object mode, switching to Wireframe, and reentering Sculpt mode. The density of the wireframe depends on the Edges value in the Multires buttons tab. However, this is not ideal. Sculpting in wireframe is much less intuitive than sculpting with a solid object. When sculpting, it is important to be looking at a shaded surface to get a full sense of the way the surface’s shape is changing.
The simple solution to this dilemma is to use Blender’s Grease Pencil feature. The Grease Pencil is a general-purpose tool that enables you to write annotations directly on the 3D view. You can set these annotations to remain with respect to the 3D viewport window or to be fixed in their position in 3D space, in which case you can dolly, zoom, or pan around them just like ordinary 3D objects. Grease Pencil is an invaluable tool for animators and people working in collaborative environments, and it is also useful for sculpting.
To use the Grease Pencil tool to set up reference sketches, follow these steps:
1. Enter Object mode. In Side view, place the 3D cursor directly in front of the sculpted face object by clicking the left mouse button (LMB), as shown in . When you use the Grease Pencil tool to sketch in 3D, the 3D cursor defines the invisible plane upon which the Grease Pencil writes. In this case, the Grease Pencil writing should be in front of the object, so that is where the 3D cursor should be set.
2. Press the Z key to toggle the view to wireframe. Open the Grease Pencil panel in the Properties Shelf of the 3D Viewport, as shown in . Click New Layer. In Object mode in the 3D viewport Tool Shelf, activate Use Sketching Sessions and click the Draw button to draw, as shown in .
3. Begin drawing with the Grease Pencil. The idea here is to sketch out the location of things to use for references, as shown in . When you begin drawing, a new Grease Pencil layer is created automatically. You can also create separate Grease Pencil layers by clicking Add New Layer. Each layer can be deleted independently of the others and has its own property settings including color, opacity, and thickness of the lines, and whether the Grease Pencil will be treated as onionskin annotations over multiple frames.
4. Give a hint of the main topological reference points of the face. Do the same thing in Side view. Remember to place your 3D cursor correctly to control where the Grease Pencil annotations appear in space. When you are satisfied with the reference annotations for both Front and Side views, turn the Grease Pencil opacity down so that the annotations are less obtrusive. You should wind up with a set of annotations that look something like the ones shown in .
5. Press the Esc key when you are ready to get out of Grease Pencil Draw mode.
You can now continue your modeling with reference to the annotations. In , you can see how the Grab tool is used to pull the mesh around the cheek area, toward the Grease Pencil annotation that indicates where the cheek should be.
Grease Pencil and Frame Changes
A primary use of the Grease Pencil tool is for animators to make annotations directly on their animations. For this reason, the tool is sensitive to the frame on which the annotations are made. Annotations on a given layer persist through frames until the next frame on which an annotation has been written. For example, if you draw a square while in frame 1 on the timeline, the square will persist through all subsequent frames. However, if you move forward to frame 10 on the timeline and draw a circle on the same Grease Pencil layer, the square will disappear on that frame and be replaced by the new annotation with the circle. After that, frames 1 through 9 will display the original square annotation, and frames from 10 on will display the circle annotation. If you want to further annotate the square itself, you must make the annotations in the same frame where the original square was drawn, namely frame 1. Onionskin enables you to see multiple frames’ worth of annotations at the same time, as though through semitransparent onionskin overlays. When making reference sketches for sculpting, Onionskin should be disabled, and you should make all your Grease Pencil annotations while on frame 1 on the timeline.
Adding Eyeballs
The simplest way to deal with eyeballs is to use ordinary mesh spheres.
1. Add a mesh sphere in Object mode by pressing the spacebar and choosing Add > Mesh > UV Sphere. Make it a UV sphere with 12 segments and 12 rings.
2. Set the sphere in place as an eyeball and adjust its size and position from Side view with reference to your Grease Pencil annotations, as shown in .
3. Use the Grab tool to adjust the mesh around the eye, as shown in .
4. Add the second eyeball by using pressing Shift+D to duplicate the first eyeball and then pressing the X key to constrain its translation to the x-axis. Position the two eyes as shown in .
5. Use Draw mode, Inflate mode, and Grab mode to get the area around the eye to match the Grease Pencil annotations from all angles and to expose the correct amount of eyeball. At this point, you should have x-axis symmetry turned off, and you should be paying attention to the asymmetries of the face.
6. It is often helpful to set the eyeball object to display only in wireframe, as shown in , particularly when refining the details of the edge of the eyelids. Do this by selecting Wire Drawtype on the Draw tab in the Object buttons area.
Refining the Nose, Mouth, and Eyes
As mentioned previously, good digital sculpting is a repeated process of rough modeling, smoothing, and refinement. The nose areas, mouth, and eyes all involve the same kind of incremental approach. From this point on, the multires level that you use will depend on what specific level of detail you are trying to refine. Obviously, the higher the multires level, the finer the detail you will be able to work with, but after a certain point, your hardware will limit how easily you can work with high resolutions. You will have to experiment with what your computer is capable of. Also remember that the multires level itself is not what determines the slowdown but rather the number of vertices. If you have already subdivided a mesh before adding multires, then the number of vertices will obviously be higher at each progressive multires level. The highest multires level used in the example in this section is level 7.
In , you can see how the subtractive Draw tool was used to roughly etch out the indentation around the edge of the nose. With any given Sculpt tool, you can sculpt in the opposite direction by holding Control while sculpting with LMB.
Again, after making the rough sculpt, go over the area with the Smooth tool, as shown in .
The Pinch tool is an important tool for creating creases and sharp edges. The Pinch tool pulls the mesh toward its center. When run along a bulge, the Pinch tool will create an edge; when run along the length of an indentation, it will pinch the indentation into the form of a crease. Use the Pinch tool as shown in to define the crease around the nose.
Take a similar approach with the mouth. shows the Inflate tool being used to add volume to the lips and the ridges under the nose. The Inflate tool is similar to the Draw tool except that instead of pulling the mesh toward or away from the view, it inflates or deflates the mesh along the mesh normals. The differences can be subtle, but they make Inflate a better tool for adding volume in cases like this.
After the lips are smoothed with the Smooth tool, the Pinch tool is used to define both the ridges along the edge of the lips and the crease between the top and bottom lips, as shown in . Note that both of these are done with the Pinch tool in additive mode. Subtractive mode for the Pinch tool pushes the mesh away from the tool’s center and is not as frequently used as the additive mode.
The same basic methodology is used to model the eyelids. In , you can see the process of adding ridges with the Draw tool, smoothing them with the Smooth tool, and then defining the crease with the Pinch tool.
Modeling Ears
To model ears, first make sure that your tools have x-axis symmetry activated, so you don’t have to model twice.
1. Begin the process by sketching out the shape of the ear with the additive Layer tool. This will start to raise the surface of the mesh in the shape of the ear to give you some material to work with, as shown in . Follow the guidelines you drew with the Grease Pencil.
2. Sculpt the shape of the ear further using the additive Draw tool for the areas that protrude and the subtractive Draw tool for the recesses, as shown in . Note that the front-view image used in this example is slightly foreshortened. The ears should protrude slightly more than they appear to in the photograph.
3. Use a light pass of the Smooth tool continually to keep the mesh tensions as balanced as possible. After you’ve coaxed the shape of the ear fully out of the side of the head, use whatever tools you need to get the shape right. The sculpting in used both additive and subtractive Layer and Draw tools as well as the Grab tool.
4. As you model, vertices may bunch up and the surface may become rough. Use the Smooth tool often to keep the mesh looking good. In , you can see how the ear looks when it has been freshly smoothed.
5. You have undoubtedly lost some detail when you smoothed, so now you need to go back over the mesh with another pass of sculpting to get it back.
6. For an intricate object like a human ear, paying close attention to a photographic reference is invaluable. Finalize the details of the ear as shown in . Create edges and creases using the Pinch tool. You can adjust the overall shape easily using the Grab tool set to a brush about half the size of the ear itself or slightly more.
The final sculpted object, with a clay material added, should look something like the one shown in . You can find the sculpted object (and the clay material used) on the CD that accompanies this book, in the file baby.blend.
With a viewport shader applied (see Chapter 2), the finished sculpture looks like in the 3D viewport.
Forging Out on Your Own
Like playing the tuba or juggling zucchinis, digital sculpting is something that you can’t really learn just by reading about it. This section has presented an overview of Blender sculpting techniques in action. These are the techniques you will need to master in order to get the most out of this powerful tool. Don’t expect too much of your first attempt at sculpting. You will improve by leaps and bounds with just a little bit of practice. Stick with it, and very soon you will find that sculpting in Blender comes as naturally as drawing a picture.
Blender Sculpting Tools and the Google Summer of Code
The integration of multiresolution modeling and sculpting tools into Blender is thanks in large part to Google’s annual Summer of Code program, which the Blender Foundation takes part in regularly. The Summer of Code program is intended in part to encourage student programmers to contribute to open-source projects by providing them with stipends to carry out development on accepted proposals over the course of a summer. For each of the past seven years, the program has sponsored hundreds of students from dozens of countries to develop code for over a hundred different open-source software projects. Most recently, Blender’s Onion Branch greatly improved the speed and UI of sculpting and also ported these sculpting improvements to other brush-based areas of Blender. This undertaking was seen to by Xiao Xiangquan, who was mentored by Tom Musgrove.
Retopologizing the Mesh
At the end of the sculpting process, you will have a detailed sculpture. There’s a problem, though. The detailed sculpture, at its highest multires level, is composed of a very large number of vertices. Even if it were editable in Edit mode, it would have far too many vertices to deal with that way. If you reduce the multires level, the sculpt detail also disappears. What’s more, the fundamental topology has not changed since the first time you subdivided the default cube. There’s nothing resembling edge loops or the kind of shape-based topology that polygon models require for good deformation and animation. In short, there’s not a lot you can do with the sculpted mesh as it is.
The solution to this problem is to use Blender’s vertex-snapping features to create a new mesh with fresh topology whose shape is identical to the sculpted mesh. You can then use normal map baking to bake the normals of the sculpted mesh to a normal-mapped texture for the low-poly mesh.
To create a retopologized mesh of the baby’s head with good topology and a lower polygon count, follow these steps:
1. In Object mode and Front view, select the completed sculpted object, press Shift+S, and then choose Cursor To Selection to snap the 3D cursor to the object’s center. Press the spacebar and choose Add > Mesh > Plane to add a plane object to the scene with the Align To View option, as shown in .
2. Enter Edit mode, switch to Right view, select all vertices, and move the plane geometry to the front of the face, as shown in . Then delete three of the vertices in the plane, leaving only a single vertex.
3. Activate snapping to closest polygons using the snapping button and menu in the 3D viewport header, shown in . Be sure to click the button to the right of the drop-down menu, which enables snapping of multiple vertices simultaneously, rather than just the active vertex.
Vertex snapping to closest polygons works by evaluating the contents of the Z buffer and snapping vertices to the mesh below, along the view axis. For this reason, it is best to work with your view directly facing the portion of the mesh you are editing.
1. Begin with the viewport in Orthogonal view (the 5 key on the number pad toggles between Orthogonal and Perspective views) and directly facing the face of the model. Move the remaining vertex to the cheek of the model with the G key. The resulting vertex will appear as shown in . When you move a selection with snapping on, the selection (in this case the vertex) will automatically cling to the polygons of the object below it. If you rotate your 3D space now, you will see that the vertex is placed on the surface of the baby’s cheek.
2. Add a Mirror modifier. Although the actual mesh is not perfectly symmetrical, it will be helpful to have the basic geometry mirrored as you go. Later, you will make the nonsymmetrical adjustments.
3. With the Mirror modifier applied, begin extruding vertices from the original vertex you placed, using either the E key to extrude or Ctrl+LMB. Extrude around the eyes as shown in .
4. You may notice at this point that some of the edges and vertices are concealed under the surface of the sculpted mesh. To see what you’re working on, check X-Ray on the Display tab of the Object properties area, as shown in . The mesh will then become completely visible.
5. Extrude edges to create faces, as shown in .
This book assumes that you know the fundamentals of mesh modeling. If you are feeling uncertain about the basic mesh modeling tools, please refer to my book Introducing Character Animation with Blender, 2nd Edition (Sybex, 2011), which includes extensive in-depth modeling tutorials that cover both box modeling and poly-by-poly extrusion modeling of the kind used in this example.
6. Assuming that you have basic mesh-modeling skills, it should be straightforward to mimic the topology you see in .
7. Model the eyes as shown in . The geometry of the nose is shown in . Extend the model around the back of the head, as shown in . Finally, model the ear, as shown in .
8. Apply the Mirror modifier by clicking the corresponding Apply button on the Modifier panel. The snapping will not happen automatically on the mirrored half of the model, but if you begin pushing vertices around, you’ll find that they will snap to the surface of the sculpted object, just as the first half did. Tweak each vertex lightly on the applied mirrored portion of the mesh, until the retopo model more accurately captures the asymmetries of the sculpted model. The full mirrored mesh should look something like the one shown in .
You may have noticed at this point that the new mesh appears smaller than the original mesh. The reason for this is that the vertices of the new mesh cling to the surface of the sculpted mesh, but the vertices of a subsurfaced mesh like the one in the example here do not represent the actual surface of the mesh as it is rendered. Rather, they represent the modeling cage—that is, the tension points that hold the subsurfaced surface in place. As you can see in , if these modeling cage verts are flush with the surface of the target mesh, the subdivided surface will be smaller. This effect diminishes with the density of the mesh. If you want the shape to be more accurate, add some extra geometry in the areas that need it.
The finished retopo-modeled mesh should look something like the one shown in with a clay material applied.
Notice that the asymmetry of the original is represented, but the finer details such as the slight wrinkling of the forehead and dimpling under the lower lip are not found in the new model. In the next section, you’ll see how to deal with this.
Normal Map Baking
You now know how to create a lower-poly, nicely topological mesh with the same shape as a high-resolution sculpted mesh. But there’s an obvious drawback. Without the high-resolution, finely subdivided mesh, a lot of the detail you sculpted is lost. It would seem that this process would at least partially defeat the whole point of sculpting in the first place. Fortunately, this is not the case. Using Blender’s normal map-baking functionality enables you to capture these details and represent them as two-dimensional textures mapped to the surface of your retopo mesh.
To do this, follow these steps:
1. In order to UV-map a texture to a shape like the head in the example, it is necessary to UV-unwrap the head. This requires marking seams. Blender has a convenient tool for marking seams. In the Mesh Options panel of the Tool Shelf buttons area, you will find the Edge Select Mode drop-down menu. By default, holding down the Alt key while clicking the right mouse button (RMB) on an edge of a mesh selects edge loops. By changing the Edge Select Mode in this menu to Tag Seam, as shown in , you can change this functionality to make Alt+RMB automatically add seams to edges. Each time you press Alt+RMB on an edge, the shortest path between that edge and the previously marked seam will be marked as a seam.
2. Mark the seams on the head as shown in . This will result in relatively undistorted unwrapping into three islands: one for the face and one for each ear.
3. Open a UV/Image editor window. In the Image menu in the header of the UV/Image editor window, select New. In the New Image dialog box, set the Width and Height values to 1024 and select UV Test Grid, as shown in . Click OK to create the test grid image in the window.
4. In the 3D view, select all the vertices of the mesh by pressing the A key, and then add a new UV texture by clicking the plus symbol by the UV Maps field in the Mesh properties area, as shown in .
5. Put your mouse over the UV/Image editor window and press the E key to unwrap the mesh. The resulting UV unwrapping should look similar to what’s shown in .
6. Switch the Draw mode to Textured with the menu in the 3D viewport window header to see how the texture maps onto the surface of the mesh, as shown in . (A color print of this image can be found in the color insert of this book.)
7. This step is where the magic happens. Using the pull-down menu, change into Object mode, select the original sculpted mesh, and then hold down the Shift key and select the new retopologized mesh. Expand the Bake tab in the Render properties area, as shown in .
8. Select Normals from the Bake Mode drop-down menu. Then, select Tangent from the Normal Space drop-down, and check Selected To Active to bake the Normals from the selected object (the sculpted mesh) to the active object (the retopoed mesh). Click Bake. Before your eyes, a normal map will be rendered to the UV test grid image you created previously, as shown in . (This image is also included in full color in the color insert of this book.) Save this image to an actual image file by choosing Save from the Image menu in the header.
9. You now have a normal map texture to apply to the material on the retopoed mesh. Create an Image texture on the material, load the normal map in the Image tab of the Texture buttons, and select Normal Map and Tangent on the Map Image tab. The texture should be set to UV on the Map Input tab of the Material properties and to Normal on the Influence tab, with a Normal value of 1.000, as shown in .
10. Render the image to see the results. As you will see, the normal map creates the illusion of detail on the surface of the lower-poly mesh. In the final render, the retopoed eyeballs have also been replaced by the original spheres. You can see all three renders side by side in , which is repeated in the color insert of this book.
Save Your Baked Images!
It bears repeating that you must save baked images (such as normal maps) as image files or risk losing them when you close and reopen Blender. The same goes for images that are painted within Blender by using the Texture Paint feature. Simply packing external data into the .blend file will not persist the images, because they do not exist as external data until they have been saved as such!
You now have one more powerful tool at your disposal for mesh modeling. As you’ve seen throughout this chapter, materials and textures are crucially linked to the modeling process. In the Bake panel, you can find a variety of other useful texture types to bake, such as Ambient Occlusion or Full Render. In Chapter 4, “Rendering and Render Engines,” you will learn much more about working with materials and textures to get exactly the effects you are after.
The Bottom Line
Get the most out of Blender’s sculpting functionality. Blender’s multires modeling and sculpting features provide a powerful and versatile set of tools for 3D sculpting. When you finish each of the exercises that follow, try showing your work on a thread in
in the Focused Critique forum to get suggestions on how you can improve it.
Master It Nothing is more important than practice for improving your skills at sculpting. Following the guidelines in this chapter, create at least three more sculptures of human heads. Try sculpting old people, women, and men. Try working from orthogonal references as described in this chapter and also try freehand from informal photographs. When you’re comfortable with heads, experiment with working on full-body sculptures. Note your impressions on the differences between the various subject matters and how they are sculpted.
Use retopo to convert a sculpted form into a polygon model with correct edge loop geometry. Blender’s retopo feature enables you to create a new model whose shape is identical to another object, making it possible to recast a very high–polygon sculpted object into a lower-polygon model with elegant edge loop geometry that can be easily deformed, animated, and rendered.
Master It Select the model you are most happy with from the previous exercise and use retopo to create a lower-poly model of the same shape. Pay attention to edge loop geometry, and keep the density of the mesh as low as you can while representing the underlying shape as accurately as possible.
Use normal map baking to capture finely sculpted detail for use on a low-poly model. In order to represent the detail of a very high–poly sculpted object, Blender enables you to bake the surface normal information of the sculpted object onto a 2D texture called a normal map, which is then used as a UV texture on the lower-poly model, yielding the illusion of a highly detailed surface.
Master It Follow the steps described in this chapter to bake a normal map from your sculpted object to the retopologized model you created in the previous exercise.
