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Sorry for the confusing title, the best way to explain it is to look at my image (don't pay attention to the lines connecting the holes and sorry for the poor quality)

I have been thinking about this for a while and I can't think about a good way to do it. Booleans would result in a very glitchy topology and very bad results when subdivided, sculpting it wouldn't be precise enough (for me) and modeling it poly-by-poly would probably take forever, not to mention quite challenging.

There is surely a good and simple way to do it, but I just cannot think of one.

enter image description here

zeffii
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u2492330
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5 Answers5

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If you use booleans and want smooth spheres as results, increase your original sphere segment counts, later on you can always retopologize if the resulting face count is too high. Starting from a highpoly mesh and working to a lower one can give acceptable results.

The implementation of Blender Booleans is from the Carve Library, this is what the blender dev has to say about how to use booleans (in another very similar question) -- link

enter image description here

The carve library has made it possible to do really nice booleans in blender, but you need sufficient geometry for the polygon based approach to retain smooth shapes.

Cleaner topology results come from being precise about matching up the level of sudivision where the objects interface each other. Taking a highly divided sphere like above and doing a difference with a scaled down sphere with identical vert count will produce more geometry than needed.

Ideally you will have similar face sizes like here:

enter image description here

Use the EdgeSplit Modifier, on smooth shaded faces, in combination with matching face sizes it looks acceptable.

enter image description here

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zeffii
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  • Thank you very much. I'm a bit ashamed to admit I've never tried it without smooth shading... Thanks for the links – u2492330 Jun 17 '13 at 09:56
  • Thanks again, I guess it can't get any better at this simplicity – u2492330 Jun 17 '13 at 12:40
  • yeah, sometimes you just need that defining bit of geometry, especially viewing side-on it's not possible to have smooth round and low poly at the same time. – zeffii Jun 17 '13 at 12:59
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You could follow the workflow below

  1. Add a multi resolution modifier and subdivide 3-4 times
  2. Smooth shade the mesh
  3. Switch to Sculpting mode
  4. Choose Inflate/Deflate brush type and set its strength to 1 and enable 'Deflate' mode and check 'Accumulate'
  5. Under Stroke panel, choose stroke method to 'Airbrush' and Rate to 1
  6. Under the Curve panel, choose the Round falloff.
  7. Continue clicking on an area and watch the dents form.

Note: This method has its limitations. Its dependent on the view you choose before sculpting the holes and the depth of the hole is not visualized unless you change the view.

Sculpting Sphere Shapes

satishgoda
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    3 problems with this method: It creates a lot of artifacts around the hole's edges, It makes it very hard to have a precise control over the hole's depth and position and the "angle" of the hole (dependent on the brush's curve) is almost impossible to get right – u2492330 Jun 17 '13 at 10:14
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    With the boolean approach, you are subdiving the source mesh a lot before applying the operation, similarly by increasing the multires subdivision count you could get rid of the artifacts. This method is not perfect but could be useful for planar surfaces.. I do agree about the view dependent and depth of the hole though.. I have updated my answer by adding a note. – satishgoda Jun 17 '13 at 10:16
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Shrinkwrap

Possibly not the best solution but you
might use shrinkwrap. It is non-destructive.
Topology is kept the same but edges are strange.

shrinkwrap solution

Róbert László Páli
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5

A few more solutions:

Displacement map

This removes the need to mess with geometry and can be a fine solution. If you all you need is the 'sense' that there is hollowing out on the surface

enter image description here

and the nodes (here collapsed to show only the used inputs, outputs and parameters)

enter image description here

MetaBalls (positive and negative spheres)

metaballs in action

Maybe you didn't realize this, but with metaballs if you go into edit mode you can set if the sphere will add or subtract from other spheres in this panel. This setting is adjustable for every metaball:

metaballs can be negative too

Stitching / Patching (classic Polygon modelling method)

Think of the mesh as a patchwork quilt, putting more effort into getting low poly meshes to follow a desired topology. This is a labour of love (or hate..depending on deadlines). Any geometry you want to mix with other geometry can be patched / stitched into place. To get good at this takes practice and patience, and demands that you master a whole bunch of tools (3D cursor, fill, snapping, transform orientations)

stitching and patching partial geometry

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zeffii
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  • I like the displacement map solution because it's the easiest way to be very precise and have a good control over the holes, and the result looks very good if the camera is at a good distance from it. – u2492330 Jun 18 '13 at 10:12
  • Yeah, and it doesn't require tonnes of geometry! – zeffii Jun 18 '13 at 19:43
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You need a face loop around the rim where the big sphere meets the carving.

  1. Duplicate the big sphere. The duplicate will be deleted lated.

  2. Shrinkwrak the original big sphere to the duplicate.

  3. Delete a portion of the sphere to cover the carving, and then some.

  4. Select the edge loop around the hole.

  5. Extrude it and scale it down some.

  6. Use "to sphere" (I never found this in any menu so I hit space and type "sphere") and hit 1 to make your loop round.

  7. Apply the shrinkwrap modifier.

  8. You may need to iterate "to sphere" and shrinkwrap a couple of times before it looks good. This is because the shrinkwrap can change the edge loop.

The rest of this you can do in a number of ways. Here is one way:

  1. Fill the hole.

  2. Inset the edge a number of times to get enough geometry for a nice carving.

  3. Make a vertex group of the geometry to be carved.

  4. Use a shrinkwrap modified to do the carving. Set the vertex group to be shrink wrapped (otherwise your whole sphere will be wrapped).

Gunslinger
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