How can get UV when material on group?

[javalitterboy]

How can get UV when material on group?.

[Anssi]

You probably cannot.

[francisquitof]

Materials must be put on the faces of you want to get a UV map.

[sWilliams]

@francisquitof is most likely correct

Here’s a bit of test code that reports UVs for the first face in the first container in the model.

model = Sketchup.active_model
ents = model.active_entities
  
grp = ents[0]  # assume the first item is a group or component
mat = grp.material
face = grp.definition.entities.grep(Sketchup::Face)[0]

unless face.material = nil
    
  face.material = mat
  
  tw = Sketchup.create_texture_writer
  uv_helper = face.get_UVHelper(true, true, tw)
  
  face.outer_loop.vertices.each do |vert|
    uvq = uv_helper.get_front_UVQ(vert.position)
    
    # "Normalize" UVQ to UV.
    # #x, #y and #z corresponds to U, V and Q respectively,
    # as SketchUp re-uses the normal Point3d objects for UVQs
    u = uvq.x / uvq.z
    v = uvq.y / uvq.z
    puts "u=#{u} v=#{v}"
  end
  
  #face.material = nil
  Sketchup.undo
  
end # if

[javalitterboy]

This is the way I use now, but I think the efficiency is too low.

[sWilliams]

I started working out the mathematics producing the projection of the image onto the surface with this model.

1234567890.skp (113.7 KB)

Now I’m waiting for the penny to drop.

[javalitterboy]

I solved the calculation under orthographic projection.

def calculate_face_uv_tr(face, mat)
  return IDENTITY unless mat
  return IDENTITY unless mat.texture
  tr = Geom::Transformation.new(ORIGIN, face.normal)
  width, height = mat.texture.width, mat.texture.height
  uv_tr = Geom::Transformation.scaling(ORIGIN, 1 / width, 1 / height, 0)
  uv_tr * tr.inverse
end

[sWilliams]

Well done.

Here’s the way I’m visualizing the question.

Also, there are often two special cases to investigate. What happens when the face normal is a straight up or straight down.

[javalitterboy]

I used a fourteen sided body test and found no problems.
The tetrahedron is formed by cutting off eight corners from a cube.

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