The build modifier in Blender is an animation tool that automatically constructs or deconstructs an object over a set amount of time. It is non-destructive and very simple to use. See the video tutorial or keep reading.
To use the build modifier, select the object you want to have built (or un-built) and go to the modifiers tab. Press “Add Modifier” and find the “Build” modifier under the generate column.
You may notice the object disappear. Don’t panic, it’s supposed to do that. It defaults to building the object (rather than deconstructing it). So if you’re on frame #1 of your animation, the object hasn’t been built yet.
The build modifier works with the faces of an object, building or deconstructing the object face-by-face. So, you may want to first decide if you want more or fewer faces in your geometry. You may want to make them more evenly sized by dividing some of your larger ones.
The build modifier is fairly simple. There are really only four controls on it.
START FRAME: The start frame is which frame in your animation you want the build modifier to start generating (or de-generating) the object. So if you want your object to start being built on frame 50, type 50 in this box. Simple enough.
LENGTH: The length is how many frames you want the building / deconstructing of the object to take. This isn’t the end frame, it’s the total number of frames for the build. So if you’re starting your animation on frame 50 and leave the default “100” in the length box, it will end on frame 150.
REVERSED: Next we have a check box option titled “reversed.” When you check this box, it causes the modifier to deconstruct the object rather than build it. So it’ll start fully constructed and at the end, it will be gone. Without the box checked, the object will begin unbuilt and end fully built.
RANDOMIZE: The final check box is to randomize the order in which the modifier builds the faces of the object. The faces will generate (or de-generate) in a random order. Below the randomize check box is a “seed” option. Any time you see a “seed” value, it is a way to choose a different randomization. So, if you don’t like the random selection, change the seed value until you do. Each one is a different randomization.
So that’s really all the options for the build modifier, but there is one thing that is commonly asked by Blender users. How do you change the order and way in which the object is built?
How to Change the Build Modifier Order
Behind the scenes in Blender, every object’s elements are sorted and given an order. So one of the faces is “face #1.” Another is “face #2” and so on. This hidden list doesn’t usually matter except that the build modifier generates an object’s faces in the order they are on this list. To change how the build modifier generates, you have to change the “sort order” of the faces.
Select the object and press “tab” to go into edit mode. Ensure you are on “face select mode” as opposed to vertex or edge select mode. Press “A” to select all of the faces of the object. Then, go to MESH in your top menu bar. Go down to “SORT ELEMENTS” and you’ll see a options for how to sort the faces of your mesh. They are as follows:
(Once you choose a sort option, go back into object mode and play your animation to see how it works)
VIEW Z AXIS: This sorts the faces, based on the current viewport view, from farthest to nearest. You can sort by nearest to farthest by selecting this option and then selecting the “reverse” option below.
VIEW X AXIS: This sorts the faces, based on the current viewport view, from left to right. You can select this option and then select “reverse” to do the opposite.
CURSOR DISTANCE: This may be the most useful. Place your cursor somewhere in the scene and choose this option to build the object based on cursor distance. The faces closest to the cursor will build first. The ones farthest away will be built last. Select this and then select “reverse” to do the opposite.
MATERIAL: This option will sort the faces by material index. Normally, the materials at the top of your material list (in the materials panel) will be built first. Then it will go down the list. You can re-order the materials in the material panels and sort again for a different order.
SELECTED: This will take whatever faces you have selected and move them to the top of the sort order. This will result in the selected faces being built before the unselected faces.
RANDOMIZE: This randomizes the order of whatever faces you have selected. The reason you would do this rather than use the “randomize” check box in the modifier panel is that you can limit it to the selected faces. You could select one portion of your mesh, randomize it, and then randomize a different portion of your mesh. Mixing and matching can create interesting build orders.
REVERSE: The reverse option reverses the order of any selected faces.
Any time you re-sort your mesh’s elements, the previous sort order acts as a tiebreaker or secondary sort order. For example, if you sorted them from top to bottom and then sorted them by material, it’d build the first material from top to bottom and then the second material from top to bottom.
Play around with the order and create some interesting builds. I have a video tutorial on the build modifier as well. Stay creative!