Meshmixer's 3D sculpting tools are somewhat basic compared to higher-end tools like Mudbox and ZBrush, however because they are combined with our dynamic remeshing infrastructure, it is possible to create extremely detailed surfaces with much lower polycounts. The images below were posted on our forum by user MagWeb, see his gallery thread for more amazing examples.
There are two classes of sculpting tools in Meshmixer - Volume and Surface brushes. Each of these is based on a very different underlying technical implementation, which means that we have significantly different capabilities in each brush. As a result, some operations can only be performed with one or the other. See the Volume Brush and Surface Brush pages for details specific to each. Some functionality that is the same between brushes is described further down on this page.
The toggle at the very top of the Brush panel, shown to the right, allows you to switch between Volume and Surface brush types In addition, the 2 hotkey will start the Volume brush, and the 3 hotkey will jump to the Surface brush.
A small bit of terminology. We have used the word "Brush" to refer to various different things in the user interface. In this manual, we will use "Brush type" or "Brush mode" to refer to Volume vs Surface Brush Tools. Each of these tools has multiple Brush Operations (or BrushOp) that it can perform. You select the current Operation using the Brushes flyout (confusing!). Sometimes we will refer to the combination of an Operation and Brush, e.g. the Zipper Brush.
To apply the selected Brush Operation, you left-click-drag and then move the mouse around. An individual application of a brush is called a "stamp". As you move the mouse, stamps are applied at regular intervals (for the Surface Brush you can change this interval). In addition, if the Flow parameter is enabled, then brush stamps will continue to be applied even if the brush is not moving.
For many of the Brush Operations, you can access an "opposite" effect by holding down the ctrl key while you make the brush stroke. For example the opposite of Inflate is to Deflate, while for a Draw brush that pushes the surface outwards, the opposite is to push the surface inwards.
Each Brush also has Strength and Size parameters. Strength defines either the "speed" or "power" of the brush. For example in a Smoothing brush, higher Strength means the brush will smooth more quickly. Size defines the area-of-effect. You can use the [ and ] hotkeys to change the brush size. For mouse control, ctrl+wheel will change the Strength, and in "meshmixer" navigation mode, the wheel will change the Size. In addition, the current Strength and Size can be modified by holding down the spacebar and using the Hotbox.
As you become more proficient at sculpting, you will find yourself switching between Brush Operations quite frequently. To make this more efficient, we have a shortcut. We store a history of the sequence of Brush Operations you have used. The left and right arrow keys step forward and backwards through this history. Note that this history is not shared between the Volume and Surface Brush Tools.
In addition to the history backward/forward, you can use shift+left/right arrow keys to cycle through the brush operations in-order.
Shared Brush Parameters
One slightly confusing aspect of the sculpting system in Meshmixer is that some parameters are shared between Brush Tools and Operations, and others are not. Specifically, the brush Size and Lazyness settings, as well as the Symmetric, Flow, SymSnap, and AlignToStroke checkboxes, and the entire Filters panel, are shared between brushes. This includes being shared between the Volume and Surface modes, and across all Operations.
However, the Size, Depth, and Spacing sliders, the Volumetric checkbox, and the entire Refinement panel, are specific to each Brush Operation, and are also not shared between the same Operation in each Brush Tool (ie the BubbleSmooth has different settings in Surface and Volume modes).
The settings that are Operation-specific are persistent across runs of Meshmixer, while the shared settings are not.
This may seem a little bit arbitrary - and it is! It is easy to encounter situations where one might prefer that a setting was, or was not, shared between brushes. But we found that the current breakdown was the most consistent.
Primary and Secondary Brushes
In both Volume and Surface brush modes, there is a concept of a Primary and Secondary Operation. In the Brushes flyouts, you will see the list of possible Secondary Operations at the bottom (see example Surface Brush panel to the right). Currently the only options for Secondary Operations are different Smoothing brushes.
To use the Secondary Operation you hold down the shift key while brushing. Note that it is possible to toggle between the primary and secondary brush within a single brush stroke (although it is usually easier to start a separate stroke).
Note that when you switch to the secondary brush, the values in the property panel will change. This is because each Brush has its own set of current parameters, as described above.
Both the Volume and Surface brushes have a Symmetry checkbox. When symmetry is enabled, a white line will appear on your model. A brush stroke applied on one side of the line will be mirrored on the other, as in the image to the right. The hotkey shift+s will toggle Symmetry on and off.
The default symmetry plane passes through the origin, and is perpendicular to the X axis (ie it is the Y-Z plane). However when the Symmetry box is checked, the small "tools" icon to the right of the label will become activated, as shown to the right. If you click this icon, the brush will switch to Set Symmetry Plane mode.
In this mode you can use the 3D transformation widget to move and rotate the symmetry plane to a different location. In addition, if you have Pivots defined in the scene, you can set the symmetry plane to the pivot by left-clicking, and repeatedly left-click to cycle through the 3 pivot axes. The Reset Symmetry Plane button restores the default plane location. Once you Accept the current location, you will be returned to the Brushing mode, with the new symmetry plane active. See the example below. Note that the symmetry plane is shared between all tools, so if you change the plane in a Sculpt brush, the planes used in the Select and Create Pivot tools will also be updated.
The Surface and Volume brushes share the Refinement panel, which is initially collapsed by default. When you expand this panel (shown to the right), you have access to five settings which are stored per-BrushOp. The defaults have been tuned for each Operation to provide a reasonable trade-off between quality and performance, but you may need to change things in some cases.
The Enable Refinement toggle allows you to completely enable or disable refinement. You can also do this with the r hotkey. Refinement is enabled by default for all Operations except the Move brush. The example below shows the effect of a brush stroke with refinement disabled (middle) and enabled (right). When disabled, the mesh vertices are moved by the brush, but the mesh connectivity does not change. So, triangles are stretched. With refinement enabled, we dynamically remesh the surface during your brush stroke, to try to always maintain a reasonable triangle quality.
In the example above, the refinement-disabled stroke creates a more pleasing surface (this would be more obvious with the wireframe disabled). It is smoother compared to the refined alternative. However, the advantage of refinement is that you can continue to sculpt and the mesh will maintain reasonable quality. We have done this below, again comparing no-refinement (left) with refinement (middle). it is obvious that without refinement, we can only deform the surface so far before it becomes impossible to add more detail, while with refinement you can continue to add detail indefinitely. The image below-right was sculpted starting from a sphere!
In fact time and available memory are the only limits to the complexity you can add to an initial shape. This is the main power of Meshmixer's sculpting brushes, which will allow you to create very detailed models without having to worry about technical details of subdivision levels, etc. The trade-off is that you have to do some more work to achieve smooth surfaces, because the brush strokes are inherently not as smooth as the Multiresolution sculpting used in Mudbox and ZBrush.
The other parameters in the Refinement panel control the remeshing algorithm (this is the same algorithm used in our Remesh tool).
Refine controls the maximum edge length of the remeshing algorithm. Edges larger than the maximum length will be split. The value of this slider (in range 0-1) is combined with the brush size, so using a larger brush means that for the same Refine setting, the target edge length will be longer. There is no visual indicator of the precise maximum edge length, you just have to try the brush.
Reduce controls the minimum edge length. Edges that are too small are collapsed. Generally this does not have to be changed, however you can entirely disable collapsing by setting this to 0. In some cases this may be necessary to preserve fine details.
Smooth controls the amount of smoothing done within the remeshing steps, as in the Remesh tool.
Finally, when Adaptivity is not zero, then instead of regular remeshing we use adaptive remeshing (ie like Adaptive Density mode of the Remesh tool). This primarily affects the Reduce / edge-collapse aspects of the remeshing. As Adaptivity increases, we try harder to preserve the surface shape as we collapse it, ie so that "important" small edges are not collapsed. Although this parameter defaults to zero, if you are working with large brushes you may need to increase it.
The example below (click to enlarge) shows the effect of Adaptivity. In each of the right 3 images, a single brush stamp has been applied, which results in one round of remeshing. In the left-middle image, Adaptivity is zero, and the large brush size (and hence large target edge length) causes the ear to be significantly resampled, and details are lost. In the next two images Adaptivity is 25 and 50, and you can see that details are increasingly preserved.
Adaptivity is a recent addition to our Sculpting tools, and although it is quite helpful, you may need to experiment to get a feel for how to use this setting.