Module: Oil

Defined in:
lib/oil.rb

Defined Under Namespace

Classes: JPEGReader, PNGReader

Constant Summary collapse

VERSION = 
"0.1.0"

Class Method Summary collapse

Class Method Details

.fix_ratio(sw, sh, boxw, boxh) ⇒ Object 



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# File 'lib/oil.rb', line 4

def self.fix_ratio(sw, sh, boxw, boxh)
  x = boxw / sw.to_f
  y = boxh / sh.to_f

  destw = boxw
  desth = boxh

  if x < y
    desth = (sh * x).round
  else
    destw = (sw * y).round
  end

  if desth < 1
    desth = 1
  end

  if destw < 1
    destw = 1
  end

  return destw, desth
end

.new(io, box_width, box_height) ⇒ Object 



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# File 'lib/oil.rb', line 46

def self.new(io, box_width, box_height)
  a = io.getc
  b = io.getc
  io.ungetc(b)
  io.ungetc(a)

  if (a == "\xFF".b && b == "\xD8".b)
    o = JPEGReader.new(io, [:COM, :APP1, :APP2])
    if (o.color_space == :RGB)
      o.out_color_space = :RGBX
    end
  elsif (a == "\x89".b && b == "P".b)
    o = PNGReader.new(io)
  else
    raise "Unknown image file format."
  end

  destw, desth = self.fix_ratio(o.width, o.height, box_width, box_height)
  pre = self.pre_scale(o.width, o.height, box_width, box_height)

  o.scale_width = destw
  o.scale_height = desth

  if o.respond_to?(:scale_denom) and pre > 0
    o.scale_denom = pre
  end

  return o
end

.pre_scale(sw, sh, dw, dh) ⇒ Object

JPEG Pre-scaling is equivalent to a box filter at an integer scale factor. We don’t use this to scale down past 4x the target image size in order to get proper bicubic scaling in the final image.



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# File 'lib/oil.rb', line 31

def self.pre_scale(sw, sh, dw, dh)
  inv_scale = sw / dw
  inv_scale /= 4

  if inv_scale >= 8
    return 8
  elsif inv_scale >= 4
    return 4
  elsif inv_scale >= 2
    return 2
  else
    return 0
  end
end