bgr-rgba.rb

module Bitmap
  def self.bgr_to_rgba(raw_bgr_array, width, height, new_dimension)
    width_padding  = new_dimension - width
    height_padding = new_dimension - height

    # First convert to array of Pixel::BGR objects
    raw_bgr_array.enum_for(:each_slice, 3).map { |a| Pixel::BGR.new(*a) }.
      reverse. # Reverse it
      map { |bgr| bgr.to_rgba }. # Map to array of Pixel::RGBA objects
      enum_for(:each_slice, width).inject([]) { |memo, row| memo << row }. # Create a 2d array based on width
      map { |row|
        row.concat( [Pixel::RGBA.blank] * width_padding )
      }.concat( [ [Pixel::RGBA.blank] * new_dimension ] * height_padding ). # Change dimensions of 2d array, adding blanks
      flatten.map { |rgba| rgba.to_a }.flatten # Flatten everything back into an array of integers
  end

  module Pixel
    class RGBA < Struct.new(:red, :green, :blue, :alpha)
      def self.blank
        new(0,0,0,0)
      end

      def to_a
        [red, green, blue, alpha]
      end
    end

    class BGR < Struct.new(:blue, :green, :red)
      def to_rgba
        RGBA.new(red, green, blue, 255)
      end
    end
  end
end

if __FILE__ == $0
  require "test/unit"
  class TestBgrToRgba < Test::Unit::TestCase
    def test_bgr_to_rgba
      width     = 2
      height    = 3
      real_size = 4 # closest power of 2

      data = [
        255, 0, 0, # 1st pixel, blue (third row)
        255, 0, 0, # 2st pixel, blue
        
        0, 255, 0, # 3nd pixel, green (second row)
        0, 255, 0, # 4nd pixel, green
        
        0, 0, 255, # 5rd pixel, red (first row)
        0, 0, 255, # 6rd pixel, red
      ]

      corrected = [
        255, 0, 0, 255, # 1st pixel, red (first row)
        255, 0, 0, 255, # 2st pixel, red
        0, 0, 0, 0,     # Empty
        0, 0, 0, 0,     # Empty
        
        0, 255, 0, 255, # 3nd pixel, green (second row)
        0, 255, 0, 255, # 4nd pixel, green
        0, 0, 0, 0,     # Empty
        0, 0, 0, 0,     # Empty
        
        0, 0, 255, 255, # 5rd pixel, blue (third row)
        0, 0, 255, 255, # 6rd pixel, blue
        0, 0, 0, 0,     # Empty
        0, 0, 0, 0,     # Empty
        
        0, 0, 0, 0,     # Empty (last row)
        0, 0, 0, 0,     # Empty
        0, 0, 0, 0,     # Empty
        0, 0, 0, 0      # Empty
      ]

      result = Bitmap.bgr_to_rgba(data, width, height, real_size)
      assert_equal corrected, result
    end
  end
end