lib/prawn/images/png.rb in prawn-1.0.0.rc1 vs lib/prawn/images/png.rb in prawn-1.0.0.rc2

@@ -167,11 +167,10 @@
           :Type             => :XObject,
           :Subtype          => :Image,
           :Height           => height,
           :Width            => width,
           :BitsPerComponent => bits,
-          :Length           => img_data.size,
           :Filter           => :FlateDecode
         )
 
         unless alpha_channel
           obj.data[:DecodeParms] = {:Predictor => 15,
@@ -180,21 +179,21 @@
                                     :Columns   => width}
         end
 
         # append the actual image data to the object as a stream
         obj << img_data
-        
+
         # sort out the colours of the image
         if palette.empty?
           obj.data[:ColorSpace] = color
         else
           # embed the colour palette in the PDF as a object stream
-          palette_obj = document.ref!(:Length => palette.size)
+          palette_obj = document.ref!({})
           palette_obj << palette
 
           # build the color space array for the image
-          obj.data[:ColorSpace] = [:Indexed, 
+          obj.data[:ColorSpace] = [:Indexed,
                                    :DeviceRGB,
                                    (palette.size / 3) -1,
                                    palette_obj]
         end
 
@@ -232,11 +231,10 @@
             :Type             => :XObject,
             :Subtype          => :Image,
             :Height           => height,
             :Width            => width,
             :BitsPerComponent => alpha_channel_bits,
-            :Length           => alpha_channel.size,
             :Filter           => :FlateDecode,
             :ColorSpace       => :DeviceGray,
             :Decode           => [0, 1]
           )
           smask_obj << alpha_channel
@@ -260,21 +258,28 @@
       end
 
       private
 
       def unfilter_image_data
-        data = Zlib::Inflate.inflate(@img_data).unpack 'C*'
+        data = Zlib::Inflate.inflate(@img_data).bytes
         @img_data = ""
         @alpha_channel = ""
 
         pixel_bytes     = pixel_bitlength / 8
         scanline_length = pixel_bytes * self.width + 1
         row = 0
         pixels = []
+        row_data = [] # reused for each row of the image
         paeth, pa, pb, pc = nil
-        until data.empty? do
-          row_data = data.slice! 0, scanline_length
+
+        data.each do |byte|
+          # accumulate a whole scanline of bytes, and then process it all at once
+          # we could do this with Enumerable#each_slice, but it allocates memory,
+          #   and we are trying to avoid that
+          row_data << byte
+          next if row_data.length < scanline_length
+          
           filter = row_data.shift
           case filter
           when 0 # None
           when 1 # Sub
             row_data.each_with_index do |byte, index|
@@ -282,26 +287,26 @@
               row_data[index] = (byte + left) % 256
               #p [byte, left, row_data[index]]
             end
           when 2 # Up
             row_data.each_with_index do |byte, index|
-              col = index / pixel_bytes
+              col = (index / pixel_bytes).floor
               upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_bytes]
               row_data[index] = (upper + byte) % 256
             end
           when 3  # Average
             row_data.each_with_index do |byte, index|
-              col = index / pixel_bytes
+              col = (index / pixel_bytes).floor
               upper = row == 0 ? 0 : pixels[row-1][col][index % pixel_bytes]
               left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes]
 
               row_data[index] = (byte + ((left + upper)/2).floor) % 256
             end
           when 4 # Paeth
             left = upper = upper_left = nil
             row_data.each_with_index do |byte, index|
-              col = index / pixel_bytes
+              col = (index / pixel_bytes).floor
 
               left = index < pixel_bytes ? 0 : row_data[index - pixel_bytes]
               if row.zero?
                 upper = upper_left = 0
               else
@@ -333,12 +338,13 @@
           row_data.each_slice pixel_bytes do |slice|
             s << slice
           end
           pixels << s
           row += 1
+          row_data.clear
         end
 
-        # convert the pixel data to seperate strings for colours and alpha
+        # convert the pixel data to separate strings for colours and alpha
         color_byte_size = self.colors * self.bits / 8
         alpha_byte_size = alpha_channel_bits / 8
         pixels.each do |this_row|
           this_row.each do |pixel|
             @img_data << pixel[0, color_byte_size].pack("C*")