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graphics3d - How to improve visibility of surfaces with opacity?


Consider this example


Graphics3D[{EdgeForm[None], Opacity[0.5],
 Blue,  Cuboid[{0, 0, 0}, {1, 1, 1/3}],
 Green, Cuboid[{0, 0, 1/3}, {1, 1, 2/3}],

 Red,   Cuboid[{0, 0, 2/3}, {1, 1, 1}],
 Gray, Opacity[1], Sphere[{1/2, 1/2, #/3 - 1/6}, 0.1] & /@ {1, 2, 3}},
Boxed -> False]

enter image description here


For the green box, the edges and the surfaces in the back are also quite visible. For blue and red boxes the contrast is much smaller. How to improve it such a way that the edges would be visible from the difference in colour and also make the balls inside visible?


One possible way can be using an extra layer with slightly different opacity


Graphics3D[{EdgeForm[None], Opacity[0.5],
  Blue, Cuboid[{0, 0, 0}, {1, 1, 1/3}],
  Green, Cuboid[{0, 0, 1/3}, {1, 1, 2/3}],

  Red, Cuboid[{0, 0, 2/3}, {1, 1, 1}],
 Opacity[0.6],
  Blue, Polygon[{{0, 0, 0}, {1, 0, 0}, {1, 1, 0}, {0, 1, 0}}],
  Red, Polygon[{{0, 0, 2/3}, {0, 1, 2/3}, {0, 1, 1}, {0, 0, 1}}],
 Gray, Opacity[1], Sphere[{1/2, 1/2, #/3 - 1/6}, 0.1] & /@ {1, 2, 3}},
 Boxed -> False]

enter image description here


For a lot of boxes, it does not seem to be a good option.



Answer




One (tedious) way is to define a box with different Opacity for different surfaces.


opqbox[{x1_, y1_, z1_}, {x2_, y2_, z2_}, {d_, u_, l_, r_, b_, f_}] := {EdgeForm[None],
           Opacity[b], Polygon[{{x1, y1, z1}, {x2, y1, z1}, {x2, y2, z1}, {x1, y2, z1}}],
           Opacity[u], Polygon[{{x1, y1, z2}, {x2, y1, z2}, {x2, y2, z2}, {x1, y2, z2}}],
           Opacity[r], Polygon[{{x1, y1, z1}, {x2, y1, z1}, {x2, y1, z2}, {x1, y1, z2}}],
           Opacity[l], Polygon[{{x1, y2, z1}, {x2, y2, z1}, {x2, y2, z2}, {x1, y2, z2}}],
           Opacity[o], Polygon[{{x1, y1, z1}, {x1, y2, z1}, {x1, y2, z2}, {x1, y1, z2}}],
           Opacity[f], Polygon[{{x2, y1, z1}, {x2, y2, z1}, {x2, y2, z2}, {x2, y1, z2}}]}



opc={0.5,0.15,0.35,0.20,0.25,0.25};
Graphics3D[{EdgeForm[None],Opacity[0.5],
            Blue,opqbox[{0,0,0},{1,1,1/3},opc],
            Green,opqbox[{0,0,1/3},{1,1,2/3},opc],
            Red,opqbox[{0,0,2/3},{1,1,1},opc],
          Gray,Opacity[1],Sphere[{1/2,1/2,#/3-1/6},0.1]&/@{1,2,3}},
Boxed->False]

enter image description here


d, u, l, r, b, f are the Opacity for down, up, left, right, back and front face.



enter image description here


This cube is made by the method suggested by Michael E2 in this answer.


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