Thicker spirals without inner faces?

j_jones

I've started playing with the Ruby api aspect of Sketchup.

I created this script to draw a spiral out of log spiral curves.


module LogSpirals

  def self.rotate_thing(thing, rotation_angle)
    rotate_transform = Geom;;Transformation.rotation([0,0,0], [0,0,1], rotation_angle.degrees)
    thing.transform!(rotate_transform)
  end 

  def self.make_material(rgb, alpha)
    model = Sketchup.active_model
    r, g, b = rgb
    color = Sketchup;;Color.new(r, g, b)
    material = model.materials.add("Rainbow Face r #{r} g #{g} b #{b} alpha #{alpha}")
    material.color = color
    material.alpha = alpha
    material
  end

  def self.color_face(face, material)
    face.material = material
    face.back_material = material
  end

  def self.create_spiral(scale_factor, growth_factor, steps, z_offset, thickness, rotation, rgb, alpha)
    model = Sketchup.active_model
    entities = model.active_entities
    
    model.start_operation("log_spiral",true,false,true)
    
    # create a spiral starting at the origin
    spiral_points = []

    (0..steps).each do |angle|
      theta = angle.degrees
      r = scale_factor * Math.exp(growth_factor * theta)
      x = r * Math.cos(theta)
      y = r * Math.sin(theta)

      # subtract 10 so the spiral starts at the origin
      x2 = (x * 100) - 10
      y2 = y * 100
      point = Geom;;Point3d.new(x2, y2, 0)
      spiral_points << point
    end

    # make a copy of the spiral offset up the z axis by z_offset    
    spiral_points2 = spiral_points.map{ |point| point.offset([0, 0, z_offset]) }


    material = self.make_material(rgb, alpha)

    # turn it into a solid with thickness
    (0...steps).each do |i|
      pts = [spiral_points[i], spiral_points[i+1], spiral_points2[i+1], spiral_points2[i]]
      # create a face along the spiral
      face = entities.add_face(pts)
      # color the face
      self.color_face(face, material)
      # extend the face to have a thickness
      face.pushpull(thickness)
    end

    # create a group out of the spiral
    spiral_group = entities.add_group(entities.to_a)
    # rotate the spiral the given degrees
    self.rotate_thing(spiral_group, rotation)
    
    # refresh the view so the spiral is drawn
    model.active_view.refresh
    model.commit_operation
  end
end #LogSpirals Module


scale_factor = 0.1
growth_factor = 0.4
steps = 360
z_offset = 10
thickness = 0
# 1          2          3        4          5          6          7         8          9           10         11       12
# yellow     yellow-g   green    green-cyan cyan       cyan-blue  blue      mage-blue  magenta     red-mage   red      orange
# 255,255,0  255,127,0  0,255,0  0,255,127  0,255,255  0,127,255  0,0,255   127,0,255  255,0,255   255,0,127  255,0,0  255,127,0
# 30,        60         90       120        150        180        210       240        270         300        330      360
color_yellow =       [255,255,0]
color_yellow_green = [127,255,0]
color_green =        [0,255,0]
color_green_cyan =   [0,255,127]
color_cyan =         [0,255,255]
color_cyan_blue =    [0,127,255]
color_blue =         [0,0,255]
color_magenta_blue = [127,0,255]
color_magenta =      [255,0,255]
color_red_magenta =  [255,0,127]
color_red =          [255,0,0]
color_orange =       [255,127,0]

colors = [color_yellow, color_yellow_green, color_green, color_green_cyan, color_cyan, color_cyan_blue, color_blue, 
  color_magenta_blue, color_magenta, color_red_magenta, color_red, color_orange]
angles = [30,60,90,120,150,180,210,240,270,300,330,360]
alpha = 0.5

# this doesn't quite work as it keeps duplicating all the work over and over
# (0...12).each do |i|
#  color = colors[i]
#  angle = angles[i]
#  spiral = LogSpirals.create_spiral(scale_factor, growth_factor, steps, z_offset, thickness, angle, color, alpha)
# end

i = 11
rotation = angles[i]
color = colors[i]
spiral = LogSpirals.create_spiral(scale_factor, growth_factor, steps, z_offset, thickness, rotation, color, alpha)

The first result is ok, but I decided I wanted to have thicker arms to each spiral.

thin spirals: https://drive.google.com/file/d/1sF3KD4oTrsLs0IzA4099fzoaGW2zUzZq/view?usp=drive_link

thin spirals

thicker spirals: https://drive.google.com/file/d/1MS-RIx5OlmCeZwGkQi9QI3zvcOLmS53K/view?usp=drive_link

thicker spirals

I sort of solved this by adding a pushpull to each face of the arm, however, this creates a bunch of overlapping and internal faces that are visible in the finished model.

Is there a way to make the arms thicker without all these internal and overlapping faces?

Thanks for any ideas
j_jones

fredo6

The method is to draw a single spiral as a group, and then just rotate them and assign them colors, as you do.

However, you need to have
[list][]the start operation outside the loop on spirals
[]the creation of a group at the beginning of the spiral generation method. You basically create the group ( group = model.active_entities.add_group) and create the faces in that group ( ee = group.entities and face = ee.add_face....)

For thickness, you need first to offset them from the origin. Otherwise, the spirals would collide at origin. You may want to draw a cylinder at origin as the starting point of the spirals. Second, there is no other way than to compute the offset of an individual spiral, which requires a little bit of calculation (there is no API for that unfortnately).

j_jones

@fredo6 said:

The method is to draw a single spiral as a group, and then just rotate them and assign them colors, as you do.

However, you need to have
[list][]the start operation outside the loop on spirals
[]the creation of a group at the beginning of the spiral generation method. You basically create the group ( group = model.active_entities.add_group) and create the faces in that group ( ee = group.entities and face = ee.add_face....)

For thickness, you need first to offset them from the origin. Otherwise, the spirals would collide at origin. You may want to draw a cylinder at origin as the starting point of the spirals. Second, there is no other way than to compute the offset of an individual spiral, which requires a little bit of calculation (there is no API for that unfortnately).

Thank you this is helpful. I see now how to create a separate group for each spiral, that will help.

As for the thickness issue, I am now trying to build my own box from each face which resulted in a new question!

fredo6

The offset of a set of faces is not equivalent to the individual offset of each face.

You have to make the calculation for the curve. Since your spiral is in 2D, it is not too complex.You either compute the intersection of the offset of each segment, or you take the bissector at each nagle and offset the vertices by the offset value divided by the cosinus of the angle.