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I want to make a texture that basically splits a sphere into 8 quadrants, and has two boxes which are place on opposite poles (since these two boxes are where more of the visual detail is in an original mesh I place them in on opposing sides of the equatorial band). I prepped a texture outside of blender and uploaded and it looks roughly like this (with all lines equal width in texture file):

enter image description here

However when you do that the lines experience a spherical contraction/expansion depending on their position in the texture. It seems the natural way would be to draw these lines and quadrants in blender instead, but how do you draw "straight" curves onto a blender texture? There isn't any UV mapping/relief required here, just need to adjust for spherical effects on mesh

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  • $\begingroup$ When you map a rectangle onto a sphere, you lose some combination of right angles and straight lines. There is no way around this. Your outer rectangles are a good example: you cannot map a line onto the pole of a sphere, which is a point-- those rectangles are going to have to be more like triangles. What I'd recommend here is to try to make a mesh that describes what you want, after which you can use selected to active texture baking to get that shape onto your sphere as a UV mapped image. $\endgroup$
    – Nathan
    Apr 28 at 21:48
  • $\begingroup$ Is this a texture you're looking for, or modelling geometry? $\endgroup$ Apr 29 at 10:44
  • $\begingroup$ Texture specifically. I suppose I could be more specific if mesh means anything more particular for blender (though I was trying to be explicit in excluding UV maps and the like) $\endgroup$
    – Skyler
    May 2 at 7:40
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Here's a view of a sphere from directly above one of the poles:

sphere from above

The orange selected vertices look like a square, don't they? that's because I used the knife tool to carefully draw "straight" lines between four of the vertices.

But let's look at the sphere from a slightly different view:

same sphere from a different angle

Notice how in 3d the "Square" doesn't have right angles or straight lines?

Next I added a seam around the equator of the sphere. (It's the red line that's outlining the equator in both drawings. In the UV editor, I selected all vertices and did a UV unwrap. Here's what you get for two hemispheres:

UV unwrapping

Notice that the apparent square is curved?

When you want to UV uwrap a sphere and draw in a box you end up with this sort of distortion. Rather than all of the quadrants being separate, I would settle for two hemispheres, I think.

To draw in the boxes, I would export the UV map and then import it into an editor to use as a guide layer for my texture painting.

Here is one way to do that:

In the UV editor, type ALT-N to bring up the new image menu:

New image menu

Give the image a name, and then make sure you've selected all of the vertices in the sphere.

You should end up with an image that looks something like this:

UV Map showing image

Next export the image to a file by typing SHIFT-ALT-S and using the dialog box. Take that image to your favorite drawing program and make it a layer. Do your drawing on it. Then, before you save the drawing, remove the layer containing the image. That'll be your texture file.

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If you wanted to put squares at the antipodes of a sphere procedurally, you could project a box through the sphere down its object-space axis to make a mask.. here, down Z:

enter image description here

For X and Y poles, just swizzle the 'Separate XYZ' outputs. The node labelled 'Size / Soften Edges' is a Map Range node. If you do soften the edge by changing the 'From Min' & 'From Max' fields there, you can make room to round the corners of the squares by 'Distance' in the Smooth Maximum.

The Meridians can be made by taking a Smooth Minimum instead of a Smooth Maximum, and all three axes can be masked in one:

enter image description here

The outputs of these clusters go to the 'Fac' of a mix of some kind.

enter image description here

You could bake the result of the procedural shader into a UV map, as a guide for texture-painting.. a Round Cube might be a better idea than a UV sphere for any intermediate steps?

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  • $\begingroup$ When you say round cube are you just saying a cube with its edges rounded to equal 1/2 the length of an edge $\endgroup$
    – Skyler
    May 2 at 7:43
  • $\begingroup$ @Skyler No. The round corners effect depends on taking a threshold on external distance-from-corners-and-edges of a straight rectangle. The smaller the rectangle relative to the threshold, the rounder the corners. If you wanted more convenient precise control of rounded corners, I think that would better be a different arrangement, a few more nodes. $\endgroup$ May 2 at 7:52

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