Transparent Cylinder with Dashed Edges only

Question

I would like to have that kind of cylinder with Dashed edges (including the bellow inner ring):

I've been trying that:

opt = {Mesh -> None, PlotStyle -> {Lighter@Black, Opacity[0.3]}}; 
Show[{
ParametricPlot3D[{r Cos@th,r Sin@th,#},{th, 0, 2 Pi},{r, 0.3, 0.31},Evaluate@opt] &/@ {0,2}, 
ParametricPlot3D[{# Cos@th,# Sin@th,z},{th, 0, 2 Pi},{z, 0, 2},Evaluate@opt] & /@ {.3, .31}} 
,PlotRange -> All, Axes -> False, Boxed -> False, ViewVertical -> {1, 0, 0}]

But I can't find out how to dash the edges.

According to that answer I've been trying that:

tube = ParametricPlot3D[2 {Cos[t], Sin[t], u}, {t, 0, 2 Pi}, {u, -5, 5}, 
                         Mesh -> None, PlotStyle -> {Opacity[0]}];
tube /. Polygon[a__] :> {EdgeForm[{Dashed}], Mesh -> All, Polygon[a]}

But it only dashes the mesh:

And belisarius has been trying that:

RegionPlot3D[1 < x x + y y < 2 && -2 < z < 2, {x, -2, 2}, {y, -2, 2}, {z, -1/2, 1/2},
             Mesh -> False, BoundaryStyle -> Directive[Red, Thick, Dashed],
             BoxRatios -> {1, 1, 1/5}, Boxed -> False, Axes -> False] 

Which doesn't give the transparency:

Thus, my question is: is it possible to construct the first picture cylinder with Dashed Edges?

Answer 1

I once wrote something to highlight the edge of graphs of $z = f(x,y)$. The key is to notice that the property of an edge is that the surface normal is orthogonal to the direction from the view point. One can construct a function for MeshFunctions that will draw the edge. The result is pretty good, but sometimes the edge lines seem thinner. I thought it might be the surface partially obscuring them.

Below the outline is updated dynamically as the little box is rotated. Because the outline is recreated when it is rotated, it cannot be rotated directly (it destroys itself when you try -- well, more precisely, the graphic being rotated is replaced by a new one).

The mesh function is parametricFaceCosine, which returns the CosineDistance of the surface normal and the vector from the view point to the point on the graph. This is equal to 1 when the vectors are orthogonal. I used the value 0.95, which draws the mesh lines slightly in front.

radius1 = 3; radius2 = 5; height = 3;
parametricFaceCosine[f_, viewPoint_] :=  (* assumes f is a function of s, t !! *)
  Function[{xx, yy, zz, ss, tt}, 
   CosineDistance[D[f, s]\[Cross]D[f, t] /. {s -> ss, t -> tt},
    {xx - viewPoint[[1]], yy - viewPoint[[2]], zz - viewPoint[[3]]}]];

DynamicModule[{viewVec, vert, caps, corners},
 With[{f1 = {radius1 Cos[t], radius1 Sin[t], s}, 
   f2 = {radius2 Cos[t], radius2 Sin[t], s}},

  viewVec = {Max[2 radius2, height] {1.3, -2.4, 2}, Scaled[{0.5, 0.5, 0.5}]};
  vert = {0, 0, 1};
  caps = RegionPlot3D[radius1^2 <= x^2 + y^2 <= radius2^2 && (z == 0 || z == height),
   {x, -radius2, radius2}, {y, -radius2, radius2}, {z, 0, height}, 
   PlotStyle -> White, BoundaryStyle -> Directive[AbsoluteDashing[8], Darker@Blue, Thick],
   Mesh -> None, NormalsFunction -> None (* for speed *)];

  Row[{
    Graphics3D[{}, (* rotation control *)
     ViewVector -> Dynamic[viewVec], ViewVertical -> Dynamic[vert], 
     PlotLabel -> "Drag to rotate", BaselinePosition -> Top],

    Dynamic@Show[ (* cylinder *)
      ParametricPlot3D[{f1, f2}, {s, 0, height}, {t, 0, 2 \[Pi]}, 
       PlotPoints -> {2, 15}, PlotStyle -> White, 
       BoundaryStyle -> None,
       Mesh -> {{0.95}}, (* edge is exactly at 1; 0.95 is slightly in front *)
       MeshFunctions -> {parametricFaceCosine[f1, viewVec[[1]]]}, 
       MeshStyle -> Directive[AbsoluteDashing[8], Darker@Blue, Thick],
       NormalsFunction -> None (* for speed *)],
      caps,
      Axes -> None, Boxed -> False, Lighting -> {{"Ambient", White}},
      ViewVector -> Dynamic[viewVec], ViewVertical -> Dynamic[vert], 
      BoxRatios -> Automatic, SphericalRegion -> True, 
      ImageSize -> 450, BaselinePosition -> Top
      ]
    }]
  ], SaveDefinitions -> True]

Answer 2

Play with numbers in AbsoluteDashing to get what you need.

RegionPlot3D[
 1 < x x + y y < 2 && -3 < z < 3, {x, -2, 2}, {y, -2, 2}, {z, -2, 2}, 
 Mesh -> False, 
 BoundaryStyle -> Directive[AbsoluteDashing[{5, 10}], Thick], 
 BoxRatios -> Automatic, Boxed -> False, Axes -> False, 
 PlotStyle -> Opacity[.2]]

Note vertical lines are not really edges in 3D - so you cannot dash them easily in 3D. In 2D though it be easy.

Graphics[{
  {Dashed, Circle[{0, 0}, {4, 3}]},
  {Dashed, Circle[{0, 0}, {2, 1.5}]},
  {Dashed, Circle[{0, -2}, {2, 1.5}, {Pi/4, Pi - Pi/4}]},
  {Dashed, Circle[{0, -3}, {4, 3}, {Pi + Pi/9, 2 Pi - Pi/9}]},
  {Dashed, Line[{{-3.8, -3.9}, {-4, 0}}]},
  {Dashed, Line[{{3.8, -3.9}, {4, 0}}]}
  }]