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I'm trying to add basic materials to a low-poly model, and was curious if there was any way to cut in edges in a circle from a single point, so I could apply materials to faces like seen in my reference image to the right. I could go through with the knife and make cuts by hand, but that seems tricky and time consuming for likely sloppy results. Any tips on how to achieve the texture pictured would be greatly appreciated.

The OP wrote in a comment:

I'm looking for a way to add edges without changing the mesh, just so I can apply materials to faces to color.

enter image description here

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  • $\begingroup$ blender.stackexchange.com/questions/5856/… $\endgroup$ – Duarte Farrajota Ramos Nov 29 '18 at 5:53
  • $\begingroup$ Please indicate any materials requirements in your question. $\endgroup$ – atomicbezierslinger Nov 29 '18 at 6:19
  • $\begingroup$ It is not possible to "add edges without changing the mesh" directly, edges form faces which form the surface. However you can work around that by creating new meshes atop of the main one and using Shrinkwrap modifier to make new meshes stick to the surface of the main one. Or you can go with textures instead of materials (unwrap the base mesh and use Texture Paint to paint desired patterns on mesh surface). $\endgroup$ – Mr Zak Nov 29 '18 at 19:11
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In your reference image, the circles are actually built in to the topology of the body.

This is the fastest way I've found so far for getting to that topology....

enter image description here

  • Starting with a cube
  • CtrlB Bevel it
  • X Delete > 'Only Faces'
  • Select edges not on triangle-corners (Select > Similar >Length), and W Subdivide once
  • All selected, F Fill faces and Remove Doubles
  • All faces selected, AltP Poke
  • All large square regions selected, in Face Mode, Loop Tools > Circle
  • All selected, ShiftAltS'To Sphere'

Now you can I Inset the circular regions as you wish, and assign materials to face selections.

To scale the circular regions with respect to the rest of the geometry, set the Transform Orientation to 'Normal', the Pivot to 'Individual Origins', and scale the selected faces with SShiftZZ

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  • $\begingroup$ There's probably a really quick way of getting there that I haven't found.. $\endgroup$ – Robin Betts Nov 29 '18 at 16:48
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Mesh LoopTools Click Circle

Mesh Loop Tools or Loops Tools is an Addon which must be installed in User Preferences. That takes 88 seconds or less.

Know that the faces of a mesh can be UV unwrapped and assigned a texture and painted.

Simplified form mesh. Clearly the more low poly your mesh, the more the hole will look like a polygon or octagon .. rather than a smooth circle with high vertex density.

enter image description here

Stages of editing left to right top to bottom. Edit Mode.

  • Yellow vertex dense cylinder
  • Blue Partial quad strip extrusion
  • Yellow Loop Cuts for local vertex density
  • Blue Two Patches cut out in square on both sides. Bridge Edge Loops

  • Yellow Mesh Loop Tool click Circle changes rectangle hole to circular hole. Select the vertices in edit more beforehand. See Side Panel. This is the step most relevant to the OP

  • Blue Proportional Editing for edge protrusion
  • Please improve this to suit you needs
  • Technique only. No artistry focus.
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  • $\begingroup$ While this is helpful, I'm looking for a way to add edges without changing the mesh, just so I can apply materials to faces to color. I'd have to make two "rings" on the model to add material to the inside faces, and while I was able to get one ring with the addon, getting another changed my mesh too far. Thanks for your help! $\endgroup$ – Keyk123 Nov 29 '18 at 5:34
  • $\begingroup$ If you found the proposed answer useful you may choose to vote up. You may also choose to vote down. Thanking someone without an up vote is unexpected. $\endgroup$ – atomicbezierslinger Nov 29 '18 at 6:06
  • $\begingroup$ Your comments indicate a need to change the requirements of the original question. Please do not add question requirements in the comments of a proposed answer. Please move the requirement change to your original question. $\endgroup$ – atomicbezierslinger Nov 29 '18 at 6:08
  • $\begingroup$ You wrote. I'd have to make two "rings" on the model to add material to the inside faces, and while I was able to get one ring with the addon, getting another changed my mesh too far. ..... This indicates probably you can use 33 seconds of actions of editing to make the changes conform to your needs. Your model can easily be corrected if your question displays the problem clearly. $\endgroup$ – atomicbezierslinger Nov 29 '18 at 6:13
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You can do this with the Knife Project using Curves as the cuts.

Duplicate your base mesh and Scale by 2, set visibility to Wire enter image description here

Now add a Bezier Circle and Parent it to the new wire mesh Ctrl+p. Set the wire mesh to have Duplication on the Faces (in the Object tab). Then in Edit mode remove all the faces you do not want. So you end up with a "orbiting" circles. enter image description here

Make sure the Circle Curve is at 0,0,0 and the Make Duplicates Real. space and search for "real". enter image description here

Now move the wire mesh and the circle curve to another layer. Delete any circles that do not fit the requirement. I delete every other one so I am left with 3. enter image description here

Select the first Circle and the select the base mesh. Enter Edit mode and line up your view. This is very important. To make I used Othographic mode and the used the Keypad keys 3(to center)4 and 6 rotate. Once you are in position active the Knife Project. You can see the results is a circle cut projected directly on to your base mesh. enter image description here

Now you can repeat that for each of the three circles. Then scale them and repeat to create the "ring".

enter image description here

Now you can go to the layer with the wire mesh and the circle and create a new Curve.

enter image description here

Here I just added Bezier circle scaled it and added another Bezier Circle and set the Spline type to Poly.

enter image description here

Remove the original Circle from the wire mesh and parent the new Curve. Make the Duplicates real and delete the unused ones.

enter image description here

Now project the new Curves.

enter image description here

All these cuts means you can now Assign materials to match.

enter image description here

As you might noticed, you could create a more complex Curve containing all the required shapes in one go rather than use the Knife Project 3 times per side.

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