refine circles sketch

Author: monkstone

processing_app/library/vecmath/vec2d/circles.rb

@@ -1,28 +1,25 @@
 #!/usr/bin/env jruby
 require 'propane'
 
+# The sketch class
 class Circles < Propane::App
   load_library :circles
 
   def settings
     size(800, 600, P2D)
   end
 
-  ## To be overriden by the Presentation Code.
   def setup
     sketch_title 'Circles'
     color_mode(HSB, 360, 100, 100, 100)
-    @c = rand(360)
-    @points = TPoints.new
-    3.times { @points << TPoint.new(Vec2D.new(rand(5..width - 5), rand(5..height - 5))) }
-    background 0
+    reset
     ellipse_mode(RADIUS)
   end
 
   def draw
     fill(0, 0, 0)
     no_stroke
-    rect(0, 0, width, height) if (frame_count % 8_000).zero?
+    reset if (frame_count % 8_000).zero?
     @points.each do |point|
       # change direction sometimes
       point.direction Vec2D.random if rand > 0.96
@@ -39,12 +36,19 @@ def draw
   end
 
   def draw_circle(pts)
-    circumcircle = Circumcircle.new(@points.vec)
+    circumcircle = Circumcircle.new(@points.positions)
     circumcircle.calculate
     center_point = circumcircle.center
     radius = circumcircle.radius
     ellipse(center_point.x, center_point.y, radius, radius)
   end
+
+  def reset
+    @c = rand(360)
+    @points = TrianglePoints.new
+    3.times { @points << TPoint.new(Vec2D.new(rand(5..width - 5), rand(5..height - 5))) }
+    background 0
+  end
 end
 
 Circles.new

processing_app/library/vecmath/vec2d/circumcircle.md

@@ -1,43 +1,3 @@
-### Dealing with processing coordinate system ###
-
-For library see `library/circles/circles.rb`
-
-If you want to create Math Sketches in processing, you need to deal with peculiar coordinate systems, where the Y-axis is inverted in theory you should be able to do.
-
-```ruby
-scale(1, -1)
-translate(0, -height)
-```
-But that will mess up any text (plus you probably need to `push_matrix` and `pop_matrix`) so it is probably simpler to create a parallel coordinate system for the math, and translate that back to the screen (using the processing `map` function or in `propane` and `JRubyArt` use `map1d`).
-
-We have done this in `circumcircle_sketch.rb` or just accept the processing coordinate system as we have with `basic_cirmcumcircle_sketch.rb` (it is much simpler).
-
-### PVector limitations ###
-
-PVector is a 3D vector, that is often used as a 2D vector, to my mind that is just plain wrong. If you evaluate the cross product of a 2D vector you get a float (you may see somewhere that a cross product does not exist for 2D vectors, but it can be useful).  The cross product of PVector yields another PVector, so cannot be used in the calculation of the area of the triangle as defined by two vectors _cf_ Vec2D:-
-
-```ruby
-a = Vec2D.new(100, 0)
-b = Vec2D.new(0, 100)
-
-a.cross(b).abs == 10_000 # or twice the area of the triangle enclosed by a, b
-
-```
-Further we can use the cross product in a test for collinearity
-
-```ruby
-
-# given 3 points in 2D space
-a = Vec2D.new(0, 0)
-b = Vec2D.new(100, 100)
-c = Vec2D.new(200, 200)
-
-(a - b).cross(b - c) == 0 # the area of the triangle is zero, so a, b, c are collinear
-
-```
-
-Also because we were able to separate the logic, we were able to confidently re-factor the Barbara Almeida sketch to use Matrix math to determine the circumcenter
-
 ### Matrix Math ###
 
 For detailed workings see [Circumcircle at Mathworld Wolfram.com][circumcircle]
@@ -55,6 +15,3 @@ yo = -by / 2 * a
 
 
 [circumcircle]:http://mathworld.wolfram.com/Circumcircle.html
-
-
-

processing_app/library/vecmath/vec2d/library/circles/lib/circumcircle.rb

@@ -9,7 +9,7 @@ def initialize(points)
 
   def calculate
     @center = Vec2D.new(-(bx / am), -(by / am))
-    @radius = center.dist(points[2]) # any point would do
+    @radius = center.dist(points[2]) # points[2] = c
   end
 
   private

processing_app/library/vecmath/vec2d/library/circles/lib/t_points.rb

@@ -3,7 +3,7 @@
 MAX_POINT = 3
 # A collection of a maximum of 3 points in the processing world
 # includes a collinearity test using Vec2D
-class TPoints
+class TrianglePoints
   extend Forwardable
   def_delegators(:@points, :each, :map, :size, :shift, :clear, :[])
   include Enumerable
@@ -20,11 +20,12 @@ def <<(pt)
   end
 
   def collinear?
-    full? ? (vec[0] - vec[1]).cross(vec[1] - vec[2]).zero? : false
+    full? ? (positions[0] - positions[1]).cross(positions[1] - positions[2]).zero? : false
   end
 
-  def vec
-    points.map { |point| point.pos }
+  # returns positions as an array of Vec2D
+  def positions
+    points.map(&:pos)
   end
 
   def full?

processing_app/library/vecmath/vec2d/library/circles/lib/triangle_point.rb

@@ -3,6 +3,7 @@
 class TPoint
   include Propane::Proxy
   attr_reader :pos, :vel, :accel, :xbound, :ybound
+  # attr_reader :width, :height # uncomment for testing
 
   def initialize(position)
     @pos = position
@@ -13,9 +14,11 @@ def initialize(position)
   end
 
   def direction(acc)
+    # direction of the acceleration is defined by the new angle
+    @accel = acc
     # magnitude of the acceleration is proportional to the angle between
     # acceleration and velocity
-    dif = accel.angle_between(vel)
+    dif = acc.angle_between(vel)
     dif = map1d(dif, 0..PI, 0.1..0.001)
     @accel = acc * dif
   end