Adding shadows to spiric sections of a torus

Question

While adding shadows to the spiric sections of a torus using the The answer to the question given by Daniel Huber, I faced a problem.

Instead of being well separated as previously, the sections overlap. How to make them well-spaced as previously with their shadows on the lower wall face?

For shadow, I used an answer by Eldo using DropShadow developed by Michael Sollami

DropShadow = ResourceFunction["DropShadow"];


seg = {{-5, -4.5}, {-4.5, -3.5}, {-3.5, 0}, {0, 3.5}, {3.5, 
    4.5}, {4.5, 5}};
shift = {-5, -3, -1, 1, 3, 5};

gr = MapThread[
   DropShadow[
     ParametricPlot3D[{0, #2, 
        0} + {(4 + Cos[\[Phi]])*Cos[\[Theta]], (4 + Cos[\[Phi]])*
         Sin[\[Theta]], Sin[\[Phi]]}, {\[Phi], 0, 2 \[Pi]}, {\[Theta],
        0, 2 \[Pi]}, 
      RegionFunction -> 
       Function[{x, y, z}, #1[[1]] < y - #2 < #1[[2]]], 
      PlotPoints -> 10, ImageSize -> 800, Axes -> False, 
      Boxed -> False, ViewPoint -> {-2, - 1.3, 1.25}], "Blur" -> 25, 
     "Color" -> Gray, "Opacity" -> .5, 
     "Offset" -> {-10, 20}] &, {seg, shift}];
Show[gr, PlotRange -> All]

Answer 1

• My answer keep the mesh with the same shape.
• Show all the parts and then use the ResourceFunction["DropShadow"].

Clear["Global`*"];
R = 4; r = 1;
g[a_, b_] := 
  RevolutionPlot3D[{R + r*Cos[t], r*Sin[t]}, {t, 0, 
    2   Pi}, {θ, 0, 2   π}, Boxed -> False, Axes -> False, 
   MeshFunctions -> {#4 &, #5 &}, 
   Mesh -> {Subdivide[0, 2  Pi, 30], Subdivide[0, 2  Pi, 40]}, 
   RegionFunction -> Function[{x, y, z, t, θ}, a <= y <= b]];
list = {g[-(R + r), -(R + r/2)], g[-(R + r/2), -R], g[-R, -(R - r)], 
   g[-(R - r), 0], g[0, R - r], g[R - r, R], g[R, R + r/2], 
   g[R + r/2, R + r]};
plot = Show[
   Table[Graphics3D[
     GeometricTransformation[list[[i]][[1]], 
      TranslationTransform[{0, 2  i, 0}]]], {i, 1, Length@list}], 
   Boxed -> False, ViewPoint -> {-2, -1.3, 1.25}];

DropShadow = ResourceFunction["DropShadow"];
DropShadow[plot, "Blur" -> 15, "Color" -> Gray, "Opacity" -> .8, 
 "Offset" -> {-10, 20}]