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Manual - Blender 2.4x

Tip: This document section describes two ways to perform Boolean operations: the "old way" (Boolean Tools) and the "new, improved way" (Boolean Modifiers). In practice, modifiers are by far the most useful today, because of the characteristics that all modifiers share (and which "old way" Boolean operations do not):

• They have a true user-interface. It's immediately obvious which object is being affected by the operation and which (other) object is the source.
• If you don't like what you see, you can re-arrange the modifiers in the stack and thereby change the order in which the modifiers are applied. (Or you can remove or disable them, and so on.)
• Like all modifiers, they can be selectively "switched on" and "switched off."

In other words, modifiers (alone) offer non-destructive editing. When you use modifiers, you haven't done anything irreversible to your model until (and unless) you choose to make the modifiers permanent by "applying" them.

[edit] Boolean Tools

[edit] Description

Boolean operations are a method of combining or subtracting solid objects from each other to create a new form. Boolean operations in Blender only work on two Mesh type objects, preferably ones that are solid, or closed, with a well defined interior and exterior surface. If more than two mesh objects are selected only the active and previously selected object are used as operands. The boolean operations also take Materials and UV-Textures into account, producing objects with Material indices or multi UV-mapped objects.

It bears repeating: these operations take place immediately and are not reversible. They used to be "the only way to do it," but you probably don't want to do things this way today. (Instead, consider them to be a gentle reminder of just how neat Boolean Modifiers are!)

[edit] Options

Using the Boolean menu (W in Object Mode) presents the following options:

Boolean operations.

• Intersect

Creates a new object whose surface encloses the volume common to both original objects.

• Union

Creates a new object whose surface encloses the total volume of both original objects.

• Difference

The only operation in which the order of selection is important, the active object is subtracted from the selected object. That is, the resulting object surface encloses a volume which is the volume belonging to the selected and inactive object, but not to the selected and active one.

• Add Intersect Modifier

A shortcut that applies a Boolean Modifier and selects Intersect in one step.

• Add Union Modifier

A shortcut that applies a Boolean Modifier and selects Union in one step.

• Add Difference Modifier

A shortcut that applies a Boolean Modifier and selects Difference in one step.

[edit] Boolean Modifiers

This sub-panel appears in the Editing Context panel group which is accessed using F9 or clicking button in the Buttons window. This sub-panel is part of the Modifier parent panel. For further information about the common panel components see the Interface section on modifiers.

Modifier panel with Boolean modifier activated.

Intersect

The available boolean operation types (Intersect/Union/Difference)

Ob

The name of the object to be used as the second operand to this modifier.

The downside of using the direct Boolean commands is that in order to change the intersection, or even apply a different operation, you need to remove the new object and redo the command. In contrast, one can use a Boolean Modifier for great flexibility and non-destructive editing.

As with all modifiers, the booleans can be enabled/disabled or even rearranged in the stack. In addition, you can move the operands and see the boolean operation applied interactively in real time!

To get the final, “definitive” object from this modifier (like with the direct Boolean tools) you need to “Apply” the modifier using the modifier’s Apply button, and to see the result you need to move the remaining operand away or switch to local view / NumPad. Until you apply the modifier, the object’s mesh will not be modified. When you apply the boolean modifier you are notified that any mesh sticky information, animation keys and vertex information will be deleted.

[edit] Examples

[edit] Intersect

The cube and the sphere have been moved to reveal the newly created object (“A”). Each face of the new object has the material properties of the corresponding surface that contributed to the new volume based on the Intersect operation.

Intersect Before.

Intersect After.

[edit] Union

The cube (“A”) and the sphere (“B”) have been moved to reveal the newly created object (“U”). “U” is now a single mesh object and the faces of the new object have the material properties of the corresponding surface that contributed to the new volume based on the Union operation.

Union example.

[edit] Difference

The Difference of two objects is not commutative in that the active object minus the inactive object does not produce the same as inactive minus active. The cube (“A”) has been subtracted from a sphere (“B”), and both have been moved to reveal the newly created object (“D”). “D” is now a single mesh object and the faces of the new object have the material properties of the corresponding surface that contributed to the new volume based on the Difference operation. D’s volume is less than B’s volume because it was decreased by subtracting part of the cube’s volume.

Difference example.

[edit] Technical Details

Visible normals.

The boolean operations rely heavily on the surface normals of each object and so it is very important that the normals are defined properly and consistently. This means each object’s normals should point outward. A good way to see the object’s normals is to turn on the visibility of normals using the Mesh Tool 1 panel; the panel is accessible from the Buttons window, using F9 and clicking Draw normals. The normals are only visible while in Edit mode. (Visible normals) is an example of a cube with its normals visible.

In the case of open objects, that is objects with holes in the surface, the interior is defined mathematically by extending the boundary faces of the object to infinity. As such, you may find that you get unexpected results for these objects. A boolean operation never affects the original objects, the result is always a new object.

Some operations will require you to move the operands or switch to local view / NumPad to see the results of the boolean operation.

[edit] Limitations & Workarounds

The number of polygons generated can be very large compared to the original meshes, especially when using complex concave objects. Furthermore, the polygons that are generated can be of poor quality, for example, very long and thin and sometimes very small. Try using the Decimate Modifier (Editing context, F9) to fix this problem.

Sometimes the boolean operation can fail with a message saying “An internal error occurred -- sorry”. If this occurs, try to move or rotate the objects just a very small amount and try again.

Manual