Compared to many 3D tools, Meshmixer's scene is pretty simple. Still, if you are new to 3D, it can be a bit overwhelming. On this page we'll explain the primary things you will work with in the 3D viewport.
Meshmixer is mainly about meshes. But in the 3D viewport, you will find several different types of objects.
Meshes are the primary object in Meshmixer. If it isn't something else, it's a Mesh.
Pivots are persistent objects in the scene that allow you to store a "frame" - 3 orthogonal axes and a 3D location. You can select and move Pivots, and many tools can use pivots in different ways. The image to the right shows the three states of pivots. A Yellow pivot means that it is a "free" pivot, while an Orange pivot is "bound" to an object, and will move with it. See the Create Pivot tool for more information on this.
A Complex is a special kind of Mesh that was added in Meshmixer 3.0. The main difference is that a Complex contains internal "sheets" of mesh, which join with the surface mesh at edge loops. Complex meshes are non-manifold, which means that many editing operations won't work on them (but some do). The image on the right shows an example. On a Complex the non-manifold edge loops are highlighted in green. With the X-Ray shader, you can see the interior structure.
Some of our tools can use anther a second mesh as a "target" object. To set the currently-selected Mesh as the active Target, you can either use the Set as Target / Clear Target items under the Actions menu, or use the ` and ~ hotkeys to set/clear. By default the Target object is rendered in semi-transparent blue, although if you prefer you can change it to be solid by un-checking Transparent Target in the View menu. The Target state is also reflected in the Object Browser, see below. The image on the right shows a sphere set as the Target object, before and after use of the Attract To Target tool.
Object Selection and Visibility
In Meshmixer, operations generally are applied to the selected object. If you just have one Mesh in the scene, then you don't need to worry about it. But if you have two or more objects, then you have to make sure you have the right one selected. You can change the selected object(s) by left-clicking. Hold shift while left-clicking to multi-select/de-select. When an object is not selected, it is drawn in a darker shade of grey, as shown in the image below-left.
You can also hide objects in the scene. When an object is hidden, you cannot select it by clicking in the scene, although you can select it using the object browser (see below). To hide (or show) the selected object, use the Ctrl/Cmd+V hotkey. If there are many hidden objects and you would like to show them all, you can quickly do that using the Ctrl/Cmd+Shift+V combo.
The Object Browser shows a list of the objects in the Scene. Initially this window is hidden, but it will appear as soon as you have multiple objects. You can toggle its visibility using Ctrl/Cmd+Shift+O, or the Show Objects Browser item under the View menu. The image to the right shows an example with three scene objects.
The leftmost column shows the object names. You can double-click to rename objects. Some names have tags appended to them that you cannot remove - for example Complex objects will always be identified by (complex). You can select, de-select, and multi-select by clicking and shift-clicking on the rows in this table.
The Magnet icons in the middle column indicates the Target state, as described above. In this image sphere.obj is set as the Target, so its icon has little squiggles (i.e. the magnet is attracting).
The Eye icons in the rightmost column show the visibility state. You can show/hide an object by clicking on these icons.
The icons in the bottom right are filters for the object list. There are currently two - objects and pivots. In this example, Pivots are hidden (the default state). Click the buttons to change the filters.
Finally in the bottom-right are two shortcut buttons, which will Duplicate and Discard the selected objects.
There are various settings to configure the 3D scene which you can find in the View menu.
Turning on Wireframe mode means that we draw all the triangle edges as black lines, for all the Meshes in the scene (below middle). Currently it is not possible to set Wireframe mode per-object. You can also use the w hotkey to toggle wireframe. If you would like thicker wireframe lines, you can add a line "WireframeLineWidth=2" to your meshmixer.ini file, under the Options category.
By default we render boundary edges of Meshes as Blue lines. You can use this setting to turn off these lines, as shown above-right. Ctrl/Cmd+Shift+b will also toggle boundaries.
The ground-plane grid in Meshmixer can be toggled on/off with this menu item. Meshmixer uses a dynamic grid which changes resolution as you zoom in, as shown in the image below. The base dimension of the grid squares is in a bit of an odd place, though. You will find it in the Units/Dimension tool property panel, labeled as Grid Size.
Show Print Bed
If you are doing 3D printing with Meshmixer, it can be very helpful to see the print bed of your printer. Particularly for things like doing support structures of auto-layout. This menu item toggles the print bed on and off. The print bed includes a label at the front showing the printer name, and a thin bounding-box visualization of the print volume.
See the Printing manual entry for more about 3D printing.