Class: RubyLabs::Canvas::Polygon

Inherits:
TkObject
  • Object
show all
Defined in:
lib/rubylabs.rb

Overview

Polygon

A Polygon object is a proxy for a Tk polygon.  

In addition to the methods defined in the TkObject base class, a method named +rotate+
will rotate a Polygon by a specified angle.

Instance Attribute Summary

Attributes inherited from TkObject

#coords, #name, #penpoint

Instance Method Summary collapse

Methods inherited from TkObject

#erase, #fill=, #lower, nextId, options, #raise, reset

Constructor Details

#initialize(a, args = {}) ⇒ Polygon

Create a new polygon. The first argument is an array of vertex coordinates. If the polygon has n vertices, the argument should be a flat array of 2*n points. Attributes of the polygon can be passed in a hash object at the end of the argument list.

Example – create a small triangle in the upper left corner of the canvas, with a black outline and green interior:

>> x = Canvas::Polygon.new([10,10,20,20,30,10], :fill => "green", :outline => "black")
=> #<RubyLabs::Canvas::Polygon ... >

:call-seq:

x = Polygon.new(a, args = {})



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# File 'lib/rubylabs.rb', line 1000

def initialize(a, args = {})
  raise "No canvas" unless @@pipe
  @name = TkObject.nextId
  @coords = a
  @penpoint = [0,0]
  cmnd = "set #{@name} [.canvas create polygon #{@coords.join(" ")} #{TkObject.options(args)}]"
  @@pipe.puts cmnd
end

Instance Method Details

#rotate(theta) ⇒ Object

Rotate the polygon by an angle theta (expressed in degrees). The object is rotated about the point defined by the first pair of (x,y) coordinates. The return value is an array with the new coordinates.

Example: Suppose x is a square with coordinates (10,10), (20,10), (20,20), and (10,20). This call will rotate it clockwise by 45 degrees and return the new vertices:

>> x.rotate(45)
=> [10.0, 10.0, 17.07, 17.07, 10.0, 24.14, 2.93, 17.07]



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# File 'lib/rubylabs.rb', line 1018

def rotate(theta)
  theta = Canvas.radians(theta)
  a = self.coords
  x0 = a[0]
  y0 = a[1]
  (0...a.length).step(2) do |i| 
    x = a[i] - x0
    y = a[i+1] - y0
    a[i]   = x0 + x * cos(theta) - y * sin(theta)
    a[i+1] = y0 + x * sin(theta) + y * cos(theta)
  end
  self.coords = a
  return a
end