Randomize object placement on faces in SketchUp

random_placement.rb

#  Randomize object placement on faces
#  Select one component and at least one ungrouped face to start

mod = Sketchup.active_model  # Open model
ent = mod.entities  # All entities in model
sel = mod.selection  # Current selection

num = 20  # Number of items to place on each face
max_rot = 360  # Rotation max. degrees
scale_var = 0.5  # Size variation

# Create a new layer/tag so that we can turn the created copies on/off
# Also add everything to a group to keep inspector manageable
clayer = mod.layers.add('Random Items')
group = mod.entities.add_group
group.layer = clayer

# Get the first component's definition from our selection
comp = sel.grep( Sketchup::ComponentInstance )[0].definition

# Get all the faces in our selection
faces = sel.grep( Sketchup::Face )

# Iterate through all selected, ungrouped faces
faces.each_with_index { |e,i|

    # Get bounding box and normal vector for face
    bbox = e.bounds
    norm = e.normal

    # Place copies on each face
    num.times {

        # Get a random point on the face's plane - based on bounding box
        pt = Geom::Point3d.new
        pt.x = bbox.min.x + rand * bbox.width
        pt.y = bbox.min.y + rand * bbox.height
        pt.z = bbox.min.z + rand * bbox.depth
        plpt = pt.project_to_plane(e.plane)

        # Some points will be off the face, ignore those. Otherwise...
        if ( e.classify_point(plpt) == Sketchup::Face::PointInside ) 

           # Scale copies randomly               
           t_sca = Geom::Transformation.scaling plpt, ( 1 - scale_var / 2 + rand * scale_var )

           # Use the following if you need to align things normal to face:
           t_loc = Geom::Transformation.new plpt, norm
           t_rot = Geom::Transformation.rotation plpt, norm, (rand * max_rot).degrees

           # Use the following if things need to point up:
           # t_loc = Geom::Transformation.new plpt, [0,0,1]
           # t_rot = Geom::Transformation.rotation plpt, [0,0,1] , (rand * max_rot).degrees

           # Now place the copy and move it to the new layer
           new = group.entities.add_instance comp, (t_rot * t_sca * t_loc)
           new.layer = clayer

           # Life is always better with some feedback while SketchUp works
           Sketchup.status_text = "Adding objects | Done with face #{(i+1).to_s}"

        end

     }

}