Add a pure Ruby implementation

lib/blurhash.rb

@@ -2,13 +2,18 @@
 
 require 'blurhash/version'
 require 'blurhash_ext'
+require 'blurhash/ruby'
 
 module Blurhash
   def self.encode(width, height, pixels, x_comp: 4, y_comp: 3)
     p = pixels.pack("C#{pixels.size}")
     return Unstable.blurHashForPixels(x_comp, y_comp, width, height, p)
   end
 
+  def self.encode_rb(width, height, pixels, x_comp: 4, y_comp: 3)
+    Ruby.blurHashForPixels(x_comp, y_comp, width, height, pixels, width * 3)
+  end
+
   def self.components(str)
     size_flag = Base83.decode83(str[0])
     y_comp    = (size_flag / 9) + 1

lib/blurhash/ruby.rb

@@ -0,0 +1,170 @@
+module Blurhash
+  # :stopdoc:
+  module Ruby
+    class ThreeDArray
+      def initialize(y, x, z)
+        @y = y
+        @x = x
+        @z = z
+        @list = Array.new(y * x * z)
+      end
+
+      def set(y, x, z, val)
+        i = z + (x * @z) + (y * @z * @x)
+        @list[i] = val
+      end
+
+      def get(y, x, z)
+        i = z + (x * @z) + (y * @z * @x)
+        @list[i]
+      end
+
+      def [](i)
+        @list.fetch(i)
+      end
+    end
+
+    class Buffer
+      attr_reader :pos
+
+      def initialize(size)
+        @pos = 0
+        @buf = "\0".b * size
+      end
+
+      def putc(c)
+        @buf.setbyte(@pos, c)
+        @pos += 1
+      end
+
+      def [](from, len)
+        @buf[from, len]
+      end
+    end
+
+    CHARACTERS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~".bytes
+
+    def self.sRGBToLinear(value)
+      v = value.to_f / 255
+      if v <= 0.04045
+        v / 12.92
+      else
+        ((v + 0.055) / 1.055) ** 2.4
+      end
+    end
+
+    def self.multiplyBasisFunction(xComponent, yComponent, width, height, rgb, bytesPerRow, factors)
+      r = g = b = 0.0
+      normalisation = (xComponent == 0 && yComponent == 0) ? 1 : 2
+
+      height.times do |y|
+        y_coef = Math.cos(Math::PI * yComponent * y / height)
+
+        width.times do |x|
+          basis = Math.cos(Math::PI * xComponent * x / width) * y_coef
+
+          r += basis * sRGBToLinear(rgb[3 * x + 0 + y * bytesPerRow]);
+          g += basis * sRGBToLinear(rgb[3 * x + 1 + y * bytesPerRow]);
+          b += basis * sRGBToLinear(rgb[3 * x + 2 + y * bytesPerRow]);
+        end
+      end
+
+      scale = normalisation.to_f / (width * height)
+      factors.set(yComponent, xComponent, 0, r * scale)
+      factors.set(yComponent, xComponent, 1, g * scale)
+      factors.set(yComponent, xComponent, 2, b * scale)
+    end
+
+
+    def self.encode_int(value, length, destination)
+      divisor = 83 ** (length - 1)
+
+      length.times do |i|
+        digit = (value / divisor) % 83
+        divisor /= 83
+        destination.putc CHARACTERS[digit]
+      end
+    end
+
+    def self.linearTosRGB(value)
+      v = max(0, min(1, value))
+      if v <= 0.0031308
+        (v * 12.92 * 255 + 0.5).to_i
+      else
+        ((1.055 * (v ** (1 / 2.4)) - 0.055) * 255 + 0.5).to_i
+      end
+    end
+
+    def self.encodeDC(r, g, b)
+      roundedR = linearTosRGB(r)
+      roundedG = linearTosRGB(g)
+      roundedB = linearTosRGB(b)
+      (roundedR << 16) + (roundedG << 8) + roundedB
+    end
+
+    def self.max(a, b)
+      [a, b].max
+    end
+
+    def self.min(a, b)
+      [a, b].min
+    end
+
+    def self.signPow(value, exp)
+      pow = value.abs ** exp
+      value < 0 ? -pow : pow
+    end
+
+    def self.encodeAC(r, g, b, maximumValue)
+      quantR = max(0, min(18, (signPow(r / maximumValue, 0.5) * 9 + 9.5).floor))
+      quantG = max(0, min(18, (signPow(g / maximumValue, 0.5) * 9 + 9.5).floor))
+      quantB = max(0, min(18, (signPow(b / maximumValue, 0.5) * 9 + 9.5).floor))
+
+      quantR * 19 * 19 + quantG * 19 + quantB;
+    end
+
+    def blurHashForPixels(xComponents, yComponents, width, height, rgb, bytesPerRow)
+      return if xComponents < 1 || xComponents > 9
+      return if yComponents < 1 || yComponents > 9
+
+      factors = ThreeDArray.new(yComponents, xComponents, 3)
+      ptr = Buffer.new(2 + 4 + (9 * 9 - 1) * 2 + 1)
+
+      yComponents.times do |y|
+        xComponents.times do |x|
+          multiplyBasisFunction(x, y, width, height, rgb, bytesPerRow, factors)
+        end
+      end
+
+      acCount = xComponents * yComponents - 1
+      sizeFlag = (xComponents - 1) + (yComponents - 1) * 9
+      encode_int(sizeFlag, 1, ptr)
+
+      if acCount > 0
+        actualMaximumValue = 0.0
+        (acCount * 3).times do |i|
+          actualMaximumValue = max(actualMaximumValue, factors[i + 3].abs)
+        end
+        quantisedMaximumValue = max(0, min(82, (actualMaximumValue * 166 - 0.5).floor))
+        maximumValue = (quantisedMaximumValue.to_f + 1) / 166
+        encode_int(quantisedMaximumValue, 1, ptr)
+      else
+        maximumValue = 1;
+        encode_int(0, 1, ptr)
+      end
+
+      encode_int(encodeDC(factors[0], factors[1], factors[2]), 4, ptr)
+
+      acCount.times do |i|
+        encode_int(
+          encodeAC(factors[i * 3 + 3], factors[i * 3 + 4], factors[i * 3 + 5], maximumValue),
+          2,
+          ptr)
+      end
+
+      ptr[0, ptr.pos]
+    end
+    module_function :blurHashForPixels
+  end
+  # :startdoc:
+end

spec/blurhash_spec.rb

@@ -8,6 +8,11 @@
       pixels = File.read(File.join(__dir__, 'fixtures', 'test.bin')).unpack('C*')
       expect(Blurhash.encode(204, 204, pixels)).to eq 'LFE.@D9F01_2%L%MIVD*9Goe-;WB'
     end
+
+    it 'works with ruby implementation' do
+      pixels = File.read(File.join(__dir__, 'fixtures', 'test.bin')).unpack('C*')
+      expect(Blurhash.encode_rb(204, 204, pixels)).to eq 'LFE.@D9F01_2%L%MIVD*9Goe-;WB'
+    end
   end
 
   describe '.components' do