Turns out the palette is actually identical to that in wh40k.pcx

scripts/try-uncompress

@@ -18,7 +18,7 @@ module Obj
     )
 
     def self.parse(data)
-      hdr = new(*data[0..SIZE - 1].unpack("V*"))
+      hdr = new(*data[0..SIZE - 1].unpack("VVVVV"))
       pp hdr
       hdr.validate!(data.bytes.size)
       hdr
@@ -28,6 +28,16 @@ module Obj
       @num_sprites, @dir_offset, @dir_size, @data_offset, @data_size = *entries
     end
 
+    def to_data
+      [
+        @num_sprites,
+        @dir_offset,
+        @dir_size,
+        @data_offset,
+        @data_size,
+      ].pack("VVVVV")
+    end
+
     def validate!(overall_size)
       raise "Directory overlaps EOF" if overall_size < dir_size + dir_offset
       raise "Data overlaps EOF" if overall_size < data_offset + data_size
@@ -62,6 +72,10 @@ module Obj
       @sprite_size = sprite_size
     end
 
+    def to_data
+      [rel_offset, sprite_size].pack("VV")
+    end
+
     def sprite_range
       rel_offset...(rel_offset+sprite_size)
     end
@@ -91,8 +105,11 @@ module Obj
       @entries = entries
     end
 
-    # Convert the directory into an Array of bytes. Until we work out how to
-    # parse sprites, anyway...
+    def to_data
+      entries.map(&:to_data).join("")
+    end
+
+    # Convert the directory into an Array of sprites
     def realize(rel_data)
       entries.map { |entry| Sprite.parse(rel_data[entry.sprite_range]) }
     end
@@ -125,6 +142,18 @@ module Obj
         @unknown20 = *args
     end
 
+    def to_data
+      [
+        @unknown0,
+        @width,
+        @height,
+        @unknown8,
+        @size,
+        @unknown16,
+        @unknown20
+      ].pack("VvvVVVV")
+    end
+
     def pixel_range
       SIZE...(SIZE+size)
     end
@@ -148,6 +177,15 @@ module Obj
       @records = records
       @raw = raw
     end
+
+    # raw is optional, so don't use it here
+    def to_data
+      header.to_data + records.join("")
+    end
+
+    def total_size
+      SpriteHeader::SIZE + records.join("").size
+    end
   end
 
   class Parsed
@@ -161,6 +199,19 @@ module Obj
       @directory = directory
       @sprites = sprites
     end
+
+    def to_data
+      dir_padding = "\x00"*(header.dir_offset - Header::SIZE)
+      data_padding = "" # for now, assume all is well
+
+      [
+        header.to_data,
+        dir_padding,
+        directory.to_data,
+        data_padding,
+        sprites.map { |sprite| sprite.to_data },
+      ].join("")
+    end
   end
 
   def self.parse(data)
@@ -383,6 +434,70 @@ def sprite(filename, i)
   end
 end
 
+# Build a test sprite to investigate the color palette
+def build(filename)
+  sprite_records = [
+    # 63 in each sprite except the last, which has just 3
+      1.upto(63).map { |b| "\x01#{b.chr}\x00" },
+     64.upto(126).map { |b| "\x01#{b.chr}\x00" },
+    127.upto(189).map { |b| "\x01#{b.chr}\x00" },
+    190.upto(252).map { |b| "\x01#{b.chr}\x00" },
+    253.upto(255).map { |b| "\x01#{b.chr}\x00" },
+  ]
+
+  sprites = sprite_records.map do |records|
+    data = records.join("")
+    header = Obj::SpriteHeader.new(
+       0, # Stolen from blank.obj
+       1, # width of 1
+      records.size, # height = number of records
+       0, # padding?
+       data.size,
+       0, # padding?
+       0, # padding?
+    )
+
+    Obj::Sprite.new(
+      header,
+      records,
+      header.to_data + data,
+    )
+  end
+
+  dir_block_offset = 32 # hardcoded
+  dir_block_size = 8 *sprites.size
+  data_block_offset = dir_block_offset + dir_block_size
+  data_block_size = sprites.inject(0) { |x, spr| x + spr.total_size }
+
+  header = Obj::Header.new(
+      sprites.size,
+      dir_block_offset,
+      dir_block_size,
+      data_block_offset,
+      data_block_size,
+  )
+
+  offset = 0
+  directory = Obj::SpriteDir.new(
+    sprites.map { |sprite|
+      puts "offset #{offset} => #{sprite.total_size}"
+      entry = Obj::DirEntry.new(offset, sprite.total_size)
+      offset += sprite.total_size
+      entry
+    }
+  )
+
+  pp directory
+
+  built = Obj::Parsed.new(
+    header,
+    directory,
+    sprites
+  )
+
+  File.open(filename, "w") { |f| f.write(built.to_data) }
+end
+
 case command = ARGV.shift
 when "sprites" then
   ARGV.each { |filename| sprites(filename) } 
@@ -396,6 +511,8 @@ when "decompress" then
   ARGV.each { |filename| decompress(filename) }
 when "correlate" then
   correlate(ARGV)
+when "build" then
+  build(ARGV[0])
 else
   puts "Unrecognized command #{command}"
   exit(1)