An OpenGLES 'LCD dot-matrix' style pixel

pixel.rb

class Pixel

  attr_reader :pointer

  Minimum  = 0.00
  Maximum  = 1.00
  Margin   = 0.15

  Vertices = [
    # 4-point triangle fan
    #
    #
    #      -1,2     0,2     1,2     2,2
    #
    #
    #      -1,1     0,1     1,1     2,1
    #                C<----B
    #                |     ^
    #                V     |
    #      -1,0     0D0    A1,0     2,0
    #
    #
    #
    #      -1,-1    0,-1    1,-1    2,-1
    #
    #
    Maximum - Margin, Minimum         , # A (x, y)
    Maximum - Margin, Maximum - Margin, # B (x, y)
    Minimum         , Maximum - Margin, # C (x, y)
    Minimum         , Minimum           # D (x, y)
  ]

  def self.create(x, y, size)
    coordinates = Hash[true, x, false, y]
    pointer     = Pointer.new(:float, Vertices.size)

    Vertices.each_with_index do |vertex, index|
      vertex += coordinates[index.even?]
      vertex *= size
      pointer[index] = vertex
    end

    new pointer
  end

  def render
    glEnableVertexAttribArray(GLKVertexAttribPosition)
    glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, 0, pointer)
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4)
    glDisableVertexAttribArray(GLKVertexAttribPosition)
  end

  def initialize(pointer)
    @pointer = pointer
  end

end

pixel = Pixel.create(45, 72, 4)
pixel.render

five_pixel_high_cube = 5.times.map do |height|
  5.times.map { |width| Pixel.create(height, width, 4) }
end

five_pixel_high_cube.flatten.map(&:render)

activate each pixel in sequence over and over (limited by refresh rate and cpu)

(simplifed to show how the pixels are used)

def viewDidLoad
  super.tap do
    # build a 3x4 grid
    @grid = 4.times.map { |height| 3.times.map { |width| Pixel.create(width, height, 20) } }
    @grid.flatten!

    @active = 0

    # setupGL and the rest of the GLES view
  end
end

def glkView(view, drawInRect:rect)
  # after clearing the GL buffer
  @grid[@active].render
end

def update
  if @active > 10
    @active = 0
  else
    @active += 1
  end
end