png.rb in prawn-2.0.0

- old
+ new

@@ -66,17 +66,13 @@
             # This chunk can only occur once and it must occur after the
             # PLTE chunk and before the IDAT chunk
             @transparency = {}
             case @color_type
             when 3
-              # Indexed colour, RGB. Each byte in this chunk is an alpha for
-              # the palette index in the PLTE ("palette") chunk up until the
-              # last non-opaque entry. Set up an array, stretching over all
-              # palette entries which will be 0 (opaque) or 1 (transparent).
-              @transparency[:indexed]  = data.read(chunk_size).unpack("C*")
-              short = 255 - @transparency[:indexed].size
-              @transparency[:indexed] += ([255] * short) if short > 0
+              raise Errors::UnsupportedImageType,
+                "Pallete-based transparency in PNG is not currently supported.\n" +
+                "See https://github.com/prawnpdf/prawn/issues/783"
             when 0
               # Greyscale. Corresponding to entries in the PLTE chunk.
               # Grey is two bytes, range 0 .. (2 ^ bit-depth) - 1
               grayval = data.read(chunk_size).unpack("n").first
               @transparency[:grayscale] = grayval
@@ -206,14 +202,9 @@
           # Use Color Key Masking (spec section 4.8.5)
           # - An array with N elements, where N is two times the number of color
           #   components.
           rgb = transparency[:rgb]
           obj.data[:Mask] = rgb.collect { |x| [x,x] }.flatten
-        elsif transparency[:indexed]
-          # TODO: broken. I was attempting to us Color Key Masking, but I think
-          #       we need to construct an SMask i think. Maybe do it inside
-          #       the PNG class, and store it in alpha_channel
-          #obj.data[:Mask] = transparency[:indexed]
         end
 
         # For PNG color types 4 and 6, the transparency data is stored as a alpha
         # channel mixed in with the main image data. The PNG class seperates
         # it out for us and makes it available via the alpha_channel attribute