Method: Pixelart::Image.calc_sample_steps

Defined in:
lib/pixelart/sample.rb

.calc_sample_steps(width, new_width, center: true, debug: false) ⇒ Object 



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# File 'lib/pixelart/sample.rb', line 5

def self.calc_sample_steps( width, new_width,
                            center: true,
                            debug: false )
  ## todo/fix: assert new_width is smaller than width
  if debug
    puts
    puts "==> from: #{width}px  to: #{new_width}px"
  end

  indexes = []

  base_step = width / new_width    ## pixels per pixel

  err_step = (width % new_width) * 2   ## multiply by 2
  denominator = new_width * 2   # denominator (in de - nenner  e.g. 1/nenner 4/nenner)

  overflow = err_step*new_width/denominator  ## todo/check - assert that div is always WITHOUT remainder!!!!!

  if debug
    puts
    puts "base_step (pixels per pixel):"
    puts "  #{base_step}     -  #{base_step} * #{new_width}px = #{base_step*new_width}px"
    puts "err_step  (in 1/#{width}*2):"
    puts "  #{err_step} / #{denominator}      - #{err_step*new_width} / #{denominator} = +#{err_step*new_width/denominator}px overflow"
    puts
  end

  # initial pixel offset
  index = 0
  err   = err_step/2   ##  note: start off with +err_step/2 to add overflow pixel in the "middle"


  index +=  if center.is_a?( Integer )
              center
            elsif center
              base_step/2
            else
               0   #  use 0px offset
            end


  new_width.times do |i|
    if err >= denominator ## overflow
      puts "    -- overflow #{err}/#{denominator} - add +1 pixel offset to #{i}"  if debug
      index += 1
      err   -= denominator
    end

    puts "  #{i} => #{index}  -- #{err} / #{denominator}"  if debug


    indexes[i] = index

    index += base_step
    err   += err_step
  end

  indexes
end