Back_material of a face

[kiesewetter]

Hallo!

I am going to set the material of a face in the following method. To avoid problems with the oriatation of the face's normal I want to set its back_material, too.
I tried it with the following code:

def status_anzeigen #funktioniert, nur das mit dem alpha wert im material inplanung noch nicht so
  mod = Sketchup.active_model
  ents = mod.entities 
  sel = mod.selection 
  mats = mod.materials
  bau_mat = mats.add "im_bau" if not bau_mat = mats["im_bau"]
  bau_mat.color = [255,127,38] 
  fertig_mat = mats.add "fertig" if not fertig_mat =mats["fertig"]
  fertig_mat.color = [211,211,211] 
  inplanung = mats.add"noch_nicht_angefangen" if not inplanung = mats["noch_nicht_angefangen"]
  inplanung.color = [176,196,222] 
  inplanung.alpha = 0.3 

  ents.each{|e|
            if e.typename == "Face"
                 start = e.get_attribute "ablauf", "baubeginn"  #attributes that were assigned to the faces before
                 ende = e.get_attribute "ablauf", "bauende"     #attributes that were assigned to the faces before
                 
                if (e.material) #checking wehther the faces current material belongs to the ones created at the top of the method, if not, save the name of the current material as an attribut
             
                   invalid_materials = ["im_bau", "fertig", "noch_nicht_angefangen"]
                   unless invalid_materials.include?( e.material.name )
                     mat_vorher = e.material.name
                     e.set_attribute("ablauf", "material", mat_vorher)
                   end
                 end
                 
                 
                 if @woche.to_i >= start.to_i && @woche.to_i < ende.to_i #@woche variable of the class
                   e.material = mats["im_bau"]
				   e.back_material = mats["im_bau"] #why doesn't it work?
                 end
                 if @woche.to_i >= ende.to_i 
                   e.material =mats["fertig"]
				   e.back_material =mats["fertig"]  #why doesn't it work?
                 end
                 if @woche.to_i < start.to_i 
                   e.material = mats["noch_nicht_angefangen"]
				   e.back_material = mats["noch_nicht_angefangen"]  #why doesn't it work?
                 end
            end
                 
           }
end

Only the "front" of the face was changed to the new material. Does anybody know what mistake I made?
Thanks for your time.
Tim

[TIG]

Well making the backs and fronts match will improve appearance BUT it won't work with many 3rd party render apps which render all back-faces a default material ignoring their actual back material - and render the front correctly - which is then facing away!
To make all materials be on both sides is straightforward...
You seems to be making it more complicated than it needs to be ?
EDIT: ALSO as Dan points out, your code is also flawed in several places... e.g. '==' compares values, but '=' sets a value!
Collect all faces in the model
faces=[];Sketchup.active_model.entities.each{|e|faces << e if e.class==Sketchup::Face}
Now look at each face and decide what to do
faces.each{|face| if face.material face.back_material=face.material else # there's no front material if face.back_material face.material=face.back_material end end }
Now all faces have the same front and back material.
The front material [if any] takes precedence over the back material.
If there's no front-material then the back material is also used on the front.

[Dan Rathbun]

Lines 6, 8 and 10:

use the comparison operator ==, not the assignment operator, =.

[kiesewetter]

But that part of the code:

if @woche.to_i >= start.to_i && @woche.to_i < ende.to_i #@woche variable of the class
    e.material = mats["im_bau"]
    e.back_material = mats["im_bau"] #why doesn't it work?
end
if @woche.to_i >= ende.to_i
    e.material =mats["fertig"]
    e.back_material =mats["fertig"]  #why doesn't it work?
end
if @woche.to_i < start.to_i
    e.material = mats["noch_nicht_angefangen"]
    e.back_material = mats["noch_nicht_angefangen"]  #why doesn't it work?
end

should have been working, shouldn't it?
I don't understand why the materials were assigned to the front, but not to the back of the face.
any idea?

[kiesewetter]

working meanwhile...

thanks for the help.