parse VRM file

parse_vrm.rb

require 'json'
require 'pp'

def parse_glb(f)
  magic = f.read(4)
  if magic != 'glTF'
    raise "magic not found: #{magic}"
  end

  version = f.read(4).unpack('I').first
  if version != 2
    raise "version: #{version} is not 2"
  end

  file_size = f.read(4).unpack('I').first

  json_str = nil
  body     = nil

  while !(f.eof)
    chunk_size = f.read(4).unpack('I').first
    chunk_type = f.read(4)
    chunk_data = f.read(chunk_size)

    case chunk_type
    when "BIN\x00"
      body = chunk_data
    when "JSON"
      json_str = chunk_data
    else
      raise "unknown chunk_type: #{chunk_type}"
    end
  end

  [JSON.parse(json_str), body]
end

open('AliciaSolid.vrm', 'rb') {|f|
  parsed, body = parse_glb(f)
  pp parsed
}