Plotting lines in 3D plots

Question

I would like to know whether it is possible to change part of the Style of a line in a 3D plot, when the line is under a surface, so that it seems obstructed by the surface. Of course I can always work this out using some elementary geometry and ViewPoint, but I want to know wether I can make this automatic.

Just to make things more clear, here is an example

graph1 = Show[
   Plot3D[{0, 1}, {x, 0, 1}, {y, 0, 1}, BoxRatios -> 1, 
    PlotStyle -> {{Opacity[0.3], Red}, {Opacity[0.3], Blue}}, 
    Mesh -> False], 
   Graphics3D[{{Thick, Line[{{1/2, 1/2, 0}, {1/2, 1/2, 1}}]}}]];

I would like to make, in the example above, the bit of the line that is seen under the plane z=1 to appear as a dashed line, but the remainder of the line should appear as a solid line.

I tried

ResourceFunction["Graphics3DSketch"][graph1]

but it did not work.

Answer 1

Here is a solution using MeshFunction and MeshShading:

graph1 = Show[
Plot3D[{0, 1}, {x, 0, 1}, {y, 0, 1}, BoxRatios -> 1,PlotStyle ->{{Opacity[0.3], Red}, {Opacity[0.3], Blue}},Mesh -> False], 
ParametricPlot3D[  {1/2, 1/2, t} , {t, 0, 2} , PlotStyle -> Thick  
, MeshFunctions -> {#3 &}, Mesh -> {{1}}
, MeshShading -> {Dashed,Automatic}  ]]