FIGURE 4-8: Suzanne!

      Joining and separating objects

      In the course of creating models for your scenes, you may need to treat separate objects as a single one, or break the parts of a single object into their own distinct objects — for example, you may accidentally add a new primitive while you’re still in Edit mode. Of course, you can simply undo, tab into Object mode, and re-add your primitive, but why act like you made a mistake and go through all those extra steps?

      There’s another way. When you add a new primitive while in Edit mode, all the elements of your new primitive are selected, and nothing from your original object is selected. If only there were a command that would let you break this primitive away from the container object and into an object of its own. Fortunately, there is. While in Edit mode, choose Mesh ⇒ Separate ⇒ Selection, and your new primitive is separated into its own object. You can also access this function by hotkey (P ⇒ Selection).

      Tab back into Object mode and select your new object. Its origin is located in the same place as its original object’s origin. To put the origin of your new object at its actual center, choose Object ⇒ Set Origin ⇒ Origin to Geometry in the 3D Viewport’s header. This Origin to Geometry operation checks the size of your object and calculates where its true center is. Then Blender places the object’s origin at that location.

You can also specify that the object’s origin be placed wherever your 3D cursor is located by choosing Object ⇒ Set Origin ⇒ Origin to 3D Cursor.

      A third option is similar to Origin to Geometry, but it moves the object’s content rather than the origin itself. Perform this operation by choosing Object ⇒ Set Origin ⇒ Geometry to Origin.

      As expected, you can also join two objects of the same type into a single object. To do so, select multiple objects. You can practice using the Box Select or Lasso Select tools, or you can simply Shift+click objects to add them to your selection. The last object you select is considered your active object and is the object that the others join into. With your objects selected, join them by choosing Object ⇒ Join from the 3D Viewport’s header or by using the Ctrl+J hotkey combination.

      UNDERSTANDING THE DIFFERENCE BETWEEN JOINS AND BOOLEANS

      This is a bit of a terminology thing. If you’ve never worked in 3D computer graphics before, you might expect that a join operation on two objects would result in a single, connected mesh. That’s not quite how it works. Earlier in this chapter, I explain that an object can consist of both linked and unlinked elements. There’s no requirement that, for example, all the vertices in a mesh object are linked by faces and edges. When you join two separate objects using Object ⇒ Join, you’re really just bundling them into the same object datablock. You aren’t changing any of the component mesh data.

      To actually merge meshes into a single linked unit, you need to either

      Creating duplicates and links

      In the section “Working with linked vertices,” earlier in this chapter, an example involved duplicating your selected vertices by using Mesh ⇒ Duplicate. As you may expect, this operation also works in Object mode (the hotkey is the same — Shift+D — but the menu item is slightly different at Object ⇒ Duplicate Objects). This duplication method is great if you intend to take an existing object and use it as a starting point to model another, more individualized object by tweaking it in Edit mode. However, suppose that you want your duplicated object to be identical to the original in Edit mode. And wouldn’t it be nice if, when you do go into Edit mode, your changes happen to the original as well as to all the duplicates? For duplicated objects that you have to edit only once, you want to use the power of linked duplicates. Linked duplicates are objects that share the same internal datablocks.

      Linking data between objects

      Linked duplicates are similar to what other programs call instance copies. The process to create a linked duplicate is pretty straightforward:

You can use a few other methods to verify that this duplicated object is, in fact, a linked duplicate. The easiest way is to tab into Edit mode on the original object or on any of the duplicates. When you do, all the linked objects appear to go into Edit mode, and any changes you make here automatically update all the other objects immediately. Figure 4-9 shows three linked duplicates of Suzanne being simultaneously modified in Edit mode.