The Complete Guide to Blender Graphics
Fracture

Fracturing in Blender is the process of breaking an object into multiple pieces.


In your video clips or games you will inevitably want to smash something into pieces. To achieve this simulation in Blender the object being smashed has to be prepared. Think of the preparation as if you had a pane of glass and had cracked it producing hair line fractures such that when the pane was touched it shatters.


Blender has two tools in the “User Preferences” window, “Add-on” listing under the “Object” category named “Object Fracture” and “Cell Fracture”.


Object Fracture


This is the simplest of the two options but without an understanding of its function it is not that simple.


To demonstrate this tool activate the “Object: Fracture Tool” Add-on in the “User Preferences” window.

In the 3D window have a cube positioned above a plane as shown in the diagram.













































































Physics in Blender Render


With the object (cube) fractured, select one of the shards. In the “Properties” window, “Physics” buttons click on “Rigid Body” to apply the physics to the selected shard. Box select all the shards in the 3D window being careful not to select the ground plane or anything else in the scene. In the “Tools Panel” at the left hand side of the 3D window go to the “Physics” tab and in the “Rigid Body Tools” panel click on “Copy From Active”. This applies the “Rigid Body Physics” to each shard.


See the cube fall and break apart on impact with the ground plane by pressing the “Play” button in the “Timeline” window. An animation is generated which you can scrub in the timeline.


Physics in Blender Game


With the object (cube) fractured “Game Physics”, type “Static” is automatically applied when using “Blender Game”. Box select all the shards in the 3D window then press the Space Bar and again, type “fracture” in the search window. Select “Setup Fracture Shards”. This applies “Rigid Body Physics” to all the shards.


In “Blender Game” press the P key to play and see the cube of shards fall, hit the ground plane and shatter.


Material Assignment


To enhance the visual display different material colors may be assigned to the exterior and interior surfaces of the shard cluster.


Have all the shards selected in the cube cluster then press Ctrl + J key to join them together into a single object.


Tab into “Edit” mode and box select the external faces of the cube cluster.






With the exterior faces selected, in the “Properties” window, “Material” buttons select a “Diffuse” material color. Press the “Assign” button to assign the material to the selected exterior faces.


In the “Material” buttons add a new material slot (Material.001) and select a different diffuse color. Remember at this point the exterior faces are selected and you are in “Edit” mode.


Press Ctrl + I key to select the interior faces. Click the “Assign” button to assign “Material 0.001” to the internal faces.


Press A key twice to deselect then select all faces. Press the P key and select “By Loose Parts”. Tab into “Object” mode.


Note that the object centre or “Origin of Geometry” is located at the centre of geometry of the last shard selected. To correct, Box select the cube cluster then press Ctrl + Alt + Shift + C key and select “Set Origin”, “Origin to Geometry”.


When the animation is played and the cluster disperses you will see the external and internal faces with the different colors.


Projectile


With the “Fracture Tools” enabled a projectile may be entered to disperse the shards or interact with any object having “Rigid Body” physics applied.


Press the spacebar to bring up the search menu. Type “fracture”. In the selection menu select “Add Projectile”.


Note: With the “Fracture” tool enabled you will also find a “Fracture Helper Objects” category in the 3D window “Add” button. The options in this category are “Bomb”, “Projectile” and “Rigid Body Recorder”. Selecting “Projectile” enters a sphere at the position of the cursor in the 3D window.


In the “Game Engine” the projectile is animated to move along the Y axis in the negative direction (opposite to the global Y direction indicated by the green arrow of the manipulation widget). To have the projectile disperse the shards of a fractured object you have to position the projectile such that it intersects the movement of the  shard cluster when the game is played.


Change the 3D window to “User Perspective” view and zoom in on the cube.


Select the cube. Press the Space Bar and type “Fracture” in the search window. Select “Fracture Object” from the list.


The “Fracture Tool” will display in the “Tools Panel” at the lower left hand side of the 3D window. Set your parameters and check “Execute” (For the demonstration use the default parameter settings).


Blender will take a few seconds to calculate the subdivisions of the cube. The subdivisions are called “Shards”. The exact time to subdivide will depend on the number of “Shards” you have set and the speed of your computer.




Warning: Limit the number of shards to a reasonable value.




When the subdivision is completed the cube is divided into separate multiple objects (Shards) clustered into the shape of the original cube. You will see the last subdivision computed highlighted. By clicking RMB you may select any of the other shards. You will see a better representation in “Wireframe” mode.


Understanding the Subdivision


The fracture subdivides the object internally into parts which are seprate objects. These objects are clustered together maintaining the physical exterior shape of the original object. The parts are called shards. The number of new objects is determined by the number of shards requested. Blender in fact creates more shards than required then randomly selects the number requested from the what has been created. This can be seen by comparing the list in the“Outliner” window and the list in the “Properties” window, “Object” button, “Browse Object to be linked” drop down menu.






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Physics


The “Object Fracture” tool is designed to be used when using “Blender Render” or “Blender Game”. In either case “Rigid Body” physics has to be applied to each shard and to any object in the scene with which they are to interact.

In regard to the ground plane in the demonstration apply “Rigid Body” physics, type “Passive”.


5 Shards Requested

8 Shards Created

Note: The subdivision is a random process. In a Blender scene with a new “Cube” the subdivision will produce a different arrangement of shards.

Note: Do not press the A key to select faces. Doing this will select both external and internal faces in the cluster. Have “Limit Selection to Visible” engaged and rotate the 3D window selecting individual faces

The Fracture Tool with Default Settings Check “Execute” After Entering Parameters

Plane Extruded on the Z axis

Front Orthographic View

Cube


Note: We are using the “Cube” object since it is the most basic shape to which the “ObjetFracture Tool” may be applied. The tool will not work with a “Plane” object unless it has been extruded.