Smooth irregular windows (with a different material) in a sphere


I have a sphere in one material and would like it to have amoeba-shaped windows in another (transparent) material. The windows must follow the curvature of the sphere. The question is how to make the edges of these windows smooth. Merely selecting vertices and then assigning the glass material results in windows with jagged edges… a more highly subdivided mesh makes it less apparent but it’s not really satisfactory. I guess I’m looking for a method to draw a shape on the sphere’s surface and have vertices added to the mesh accordingly, rather than using the existing regularly spaced vertices? Any ideas? Thanks!

Edit: the knife tool seems to be sort of what I’m looking for – selecting [A]ll, then [K] and draw. However:

  • that results in new vertices in the right places, but all vertices being selected rather than just the ones I need to assign the new material to (or rather, the faces within their boundary)
  • drawing with K on one side of the sphere also seems to draw on the opposite side, even when I click the ‘limit selection to visible’ button
  • the drawn boundary is not one clean ‘string’ of new vertices, but a messier double or triple string

I can think of two ways here.

  1. Turn on the retopo button (mesh panel). Now draw the shape of your windows with vertices in a new empty mesh. The new vertices should “stick” to the anything behind them in the viewport, which you should ensure is the sphere. (or you could draw first and then click retopo all).
    Then join the mesh with the sphere (Ctrl+J), do the usual merging (Alt+M).

  2. Just use a texture to either affect the transparency and color value.