class Graphics::Trail

A simple “trail” class, that draws the path of a in a particular hue.

# ... in initialize
self.trail = Trail.new self, 100, :white

# ... in Body#update
trail << body

# ... in Body#draw
trail.draw

Attributes

a[RW]

The array of x/y coordinates of the trail.

c[RW]

The hues to draw in the trail.

max[RW]

The maximum number of segments to keep in the trail.

w[RW]

The windowing system we’re drawing in.

Public Class Methods

new(w, max, color = :green) click to toggle source

Create a Trail with max length and of a particular color hue.

# File lib/graphics/trail.rb, line 40
def initialize w, max, color = :green
  self.w = w
  self.a = []
  self.max = max
  unless @@c[color] then
    @@c[color] ||= (0..99).map { |n| ("%s%02d" % [color, n]).to_sym }.reverse
  end
  self.c = @@c[color]
end

Public Instance Methods

<<(body) click to toggle source

Add another segment to the trail, and remove a segment if needed.

# File lib/graphics/trail.rb, line 63
def << body
  a << [body.x, body.y]
  a.shift if a.size > max
  nil
end

draw() click to toggle source

Draw the trail and taper off the color as we go.

# File lib/graphics/trail.rb, line 53
def draw
  m = 100.0 / max
  a.reverse_each.each_cons(2).with_index do |((x1, y1), (x2, y2)), i|
    w.line x1, y1, x2, y2, c[(i*m).round] || :black
  end
end