Using ruby Matrix in JRubyArt

###############
# Frame of Reference example by Ira Greenberg
# https://github.com/irajgreenberg/ProcessingTips
# Translated to JRubyArt by Martin Prout December 2015
###############

load_library :geometry

FACE_COUNT = 50

attr_reader :c, :p, :renderer

def settings
  size(800, 800, P3D)
end

def setup
  sketch_title 'Frame Of Reference'
  ArcBall.init(self) # so we use mouse to rotate sketch and mouse wheel to zoom
  @renderer = AppRender.new(self) # so we can render Vec3D as vertices
  @c = []
  @p = []
  FACE_COUNT.times do |i|
    # calc some random triangles in 3 space
    val = Vec3D.new(
      rand(-width / 2..width / 2),
      rand(-width / 2..width / 2),
      rand(-width / 2..width / 2)
    )
    v0 = Vec3D.new(
      rand(-val.x..-val.x + 100),
      rand(-val.y..-val.y + 100),
      rand(-val.z..-val.z + 100)
    )
    v1 = Vec3D.new(
      rand(-val.x..-val.x + 100),
      rand(-val.y..-val.y + 100),
      rand(-val.z..-val.z + 100)
    )
    v2 = Vec3D.new(
      rand(-val.x..-val.x + 100),
      rand(-val.y..-val.y + 100),
      rand(-val.z..-val.z + 100)
    )
    p << Plane.new([v0, v1, v2])
    # build some cute little cylinders
    c << Cylinder.new(Vec3D.new(150, 5, 5), 12)
    # Using each Triangle normal (N),
    # One of the Triangle's edges as a tangent (T)
    # Calculate a bi-normal (B) using the cross-product between each N and T
    # Note caps represent constants in ruby so we used N = nn, T = tt and B = bb
    # in the ruby code below

    #
    # A picture helps
    # nice, sweet orthogonal axes

    # N   B
    # |  /
    # | /
    # |/____T

    #
    # N, T, B together give you a Frame of Reference (cute little local coordinate
    # system), based on each triangle. You can then take the cylinder (or any
    # vertices) and transform them using a 3 x 3 matrix to this coordinate system.
    # (In the matrix each column is based on N, T and B respecivley.)
    # The transform will handle any rotations and scaling, but not the translation,
    # but we can add another dimenson to the matrix to hold the translation values.
    # Here's what all this confusing description looks like:

    #
    # Matrix :                               Vector :
    # |  N.x  T.x  B.x  translation.x  |      |  x  |
    # |  N.y  T.y  B.y  translation.y  |      |  y  |
    # |  N.z  T.z  B.z  translation.z  |      |  z  |
    # |  0    0    0    1              |      |  1  |

    # We add the extra row in the matrix and the 1 to each vector
    # so the math works. We describe the Matrix as 4 rows by 4 columns
    # and the vector now as a Matrix with 4 rows and 1 column.
    # When you multiply matrices the inner numbers MUST match, so:
    # [4 x 4] [4 x 1] is OK, but [4 x 4] [1 x 4] is NOT COOL.
    # see mat4.rb where we use ruby Matrix to handle the multiplication for us

    nn = p[i].n
    tt = Vec3D.new(
      p[i].vecs[1].x - p[i].vecs[0].x,
      p[i].vecs[1].y - p[i].vecs[0].y,
      p[i].vecs[1].z - p[i].vecs[0].z
    )
    nn.normalize!
    tt.normalize!
    bb = nn.cross(tt)
    # build matrix with frame and translation (to centroid of each triangle)
    m4 = Mat4.new(xaxis: nn, yaxis: tt, zaxis: bb, translate: p[i].c)
    # transform each cylinder to align with each triangle
    c[i].vecs = m4.mult(c[i].vecs)
  end
  fill(187)
  stroke(50, 20)
end

def draw
  background(0)
  lights
  FACE_COUNT.times do |i|
    p[i].display(renderer)
    c[i].display(renderer)
  end
end

class Cylinder
  include Processing::Proxy
  attr_accessor :vecs
  attr_reader :detail, :dim

  def initialize(dim, detail)
    @dim = dim
    @detail = detail
    init
  end

  def init
    #    created around x-axis
    #    y = Math.cos
    #    z = Math.sin
    veca = []
    vecb = []
    (0...360).step(360 / detail) do |theta|
      cost = DegLut.cos(theta)
      sint = DegLut.sin(theta)
      veca << Vec3D.new(0, cost * dim.y, sint * dim.z)
      vecb << Vec3D.new(dim.x, cost * dim.y, sint * dim.z)
    end
    @vecs = veca.concat(vecb)
  end

  def display(renderer)
    begin_shape(QUADS)
    detail.times do |i|
      if i < (detail - 1)
        vecs[i].to_vertex(renderer)
        vecs[i + 1].to_vertex(renderer)
        vecs[detail + i + 1].to_vertex(renderer)
        vecs[detail + i].to_vertex(renderer)
      else
        vecs[i].to_vertex(renderer)
        vecs[0].to_vertex(renderer)
        vecs[detail].to_vertex(renderer)
        vecs[detail + i].to_vertex(renderer)
      end
    end
    end_shape
  end
end

NORM_LEN = 225.0

class Plane
  include Processing::Proxy
  attr_reader :vecs, :c, :n

  def initialize(vecs)
    @vecs = vecs
    init
  end

  def init
    v1 = vecs[1] - vecs[0]
    v2 = vecs[2] - vecs[0]

    @c = Vec3D.new(
      (vecs[0].x + vecs[1].x + vecs[2].x) / 3,
      (vecs[0].y + vecs[1].y + vecs[2].y) / 3,
      (vecs[0].z + vecs[1].z + vecs[2].z) / 3
    )

    @n = v1.cross(v2)
    n.normalize!
  end

  def display(renderer)
    begin_shape(TRIANGLES)
    vecs.map { |vec| vec.to_vertex(renderer) }
    end_shape

    # normal
    stroke(200, 160, 30)
    begin_shape(LINES)
    c.to_vertex(renderer)
    (c + n * NORM_LEN).to_vertex(renderer)
    end_shape

    # binormal
    stroke(160, 200, 30)
    begin_shape(LINES)
    c.to_vertex(renderer)
    # tangent
    v = vecs[1].copy
    v -= vecs[0]
    v.normalize!
    (c + v * NORM_LEN).to_vertex(renderer)
    end_shape

    stroke(30, 200, 160)
    begin_shape(LINES)
    c.to_vertex(renderer)
    b = v.cross(n)
    (c + b * NORM_LEN).to_vertex(renderer)
    end_shape
    stroke(0, 75)
  end
end

# uber simple Homogeneous 4 x 4 matrix
require 'matrix'

class Mat4
  attr_reader :mat

  def initialize(xaxis:, yaxis:, zaxis:, translate:)
    @mat = Matrix[
    [xaxis.x, yaxis.x, zaxis.x, translate.x],
    [xaxis.y, yaxis.y, zaxis.y, translate.y],
    [xaxis.z, yaxis.z, zaxis.z, translate.z],
    [0, 0, 0, 1]
    ]
  end

  # Ira's processing version changes the input 'array', here we return
  # a new array with transformed values (which we then assign to the input)
  # see frame_of_reference.rb

  def mult(array)
    array.map.each do |arr|
      matrix_to_vector(mat * Matrix[[arr.x], [arr.y], [arr.z], [1]])
    end
  end

  private

  # It isn't obvious but we only require first 3 elements
  def matrix_to_vector(vec)
    Vec3D.new(vec.column(0)[0], vec.column(0)[1], vec.column(0)[2])
  end
end