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I want to make a mesh object that looks like the outside surface of cubes stacked in the shape of a sphere. I thought I saw this once, but I can't find it.

The final size will be big (up to 100x100x100 cubes) so I think making a million cubes and merging them (modifier Boolean Union) is going to take quite a while, especially if I have to do it differently for every frame.

As a first step, I've stacked cubes in a hollow spherical shell.

What I really want is just a single mesh object of the outside surface. But for 100x100x100 that's a million cubes to Union. There must be an easier way? 2) if not, how can I select say 20,000 cubes in a "shell" and Union them at once?

Through brute-force application of logic & math & coffee, I guess one could define an algorithm to generate the mesh directly, but I somehow think that I saw this done before in an elegant way. "cubification"? "cubation"?

Here's an example of a small shell that takes about ten seconds to generate. In the picture I've removed the top.

enter image description here

import bpy
import numpy as np

nx, ny, nz = 21, 21, 21
x0, y0, z0 = 10, 10, 10
r1, r2 = 6.0, 7.4

scale = 0.5

x, y, z = np.arange(nx), np.arange(ny), np.arange(nz)

rsq = (x[None, None, :]-x0)**2 + (y[None, :, None]-y0)**2 + (z[:, None, None]-z0)**2
sphere_1 = rsq < r1**2
sphere_2 = rsq < r2**2
shell = sphere_2 * (-sphere_1)    # I love python!

X, Y, Z = np.meshgrid(x, y, z)

ipoints = zip( X.flatten(), 
               Y.flatten(), 
               Z.flatten() )

points = zip(scale*(X.flatten()-x0), 
             scale*(Y.flatten()-y0), 
             scale*(Z.flatten()-z0) ) 

points = [thing for thing in points]  # convert zip object to list (python 3!)
ipoints = [thing for thing in ipoints]

points_shell = [thing for i,thing in enumerate(points)
                 if shell[ipoints[i]]]

for point in points_shell:
    bpy.ops.mesh.primitive_cube_add(radius=0.5*scale, location=point)
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I think you are on the right track here, but the slowest part is the creation of all the primitives. (reason - each new object's name must be checked for name collisions, and this gets progressively slower as more objects are added, it's not something we can prevent, via python)

Instead use from_pydata and generate the cube data as a function of the their center x,y,z and then extend the verts and face indices that way. Lateron you can do a post processing step which removes all the redundant (inner) faces

As related question / answer here: Extruding problem shows how to construct the pydata for cubes in one massive list

Here this is rather fast, but doesn't remove redundant geometry -- but it is miles faster than adding primitives: https://gist.github.com/zeffii/7ef17b4932e61ee12221

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  • $\begingroup$ Great! Thank you sensei @zeffii for the homework. This is good stuff! $\endgroup$ – uhoh Jul 8 '15 at 10:58
  • $\begingroup$ removing the redundant geometry is an interesting problem, which I don't have a ready-coded solution for, but the fact that this is a quantized object makes several approaches easier. $\endgroup$ – zeffii Jul 8 '15 at 11:23
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One possible way to do this would be to use the 'Remesh' modifier. It has an option to turn the selected object into blocks, though specifying the exact amount of blocks may be a bit difficult.

Here I have a UV Sphere with a remesh modifier set to 'Blocks'. I also added a Subsurf modifier before it so that the surface is smoother for the remesh:

enter image description here

You can use the 'Octree Depth' property to increase the resolution, but it will get increasingly slow when increasing this number.

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  • $\begingroup$ Fantastic! Thank you @RayMairlot. I thought it might be in there somewhere. I hit apply, and bingo, exactly what I need. Now I can skip the logic and math and go directly to the coffee. $\endgroup$ – uhoh Jul 7 '15 at 23:38
  • $\begingroup$ I've asked a follow-up question about this algorithm here. $\endgroup$ – uhoh Jul 7 '15 at 23:51

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