Class: PNGlitch::Scanline

Inherits:
Object
  • Object
show all
Defined in:
lib/pnglitch/scanline.rb

Overview

Scanline is the class that represents a particular PNG image scanline.

It consists of a filter type and a filtered pixel data.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(io, start_at, data_size, at, &block) ⇒ Scanline

Instanciate.



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# File 'lib/pnglitch/scanline.rb', line 14

def initialize io, start_at, data_size, at, &block
  @index = at
  @io = io
  @start_at = start_at
  @data_size = data_size

  pos = @io.pos
  @io.pos = @start_at
  @filter_type = @io.read(1).unpack('C').first
  @io.pos = pos

  @data = nil
  @prev_filter_type = nil
  @filter_codec = { encoder: nil, decoder: nil }

  if block_given?
    @callback = block
  end
end

Instance Attribute Details

#filter_codec ⇒ Object (readonly)

Returns the value of attribute filter_codec.



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# File 'lib/pnglitch/scanline.rb', line 9

def filter_codec
  @filter_codec
end

#filter_type ⇒ Object (readonly)

Returns the value of attribute filter_type.



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# File 'lib/pnglitch/scanline.rb', line 9

def filter_type
  @filter_type
end

#index ⇒ Object (readonly)

Returns the value of attribute index.



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# File 'lib/pnglitch/scanline.rb', line 9

def index
  @index
end

#prev_filter_type ⇒ Object (readonly)

Returns the value of attribute prev_filter_type.



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# File 'lib/pnglitch/scanline.rb', line 9

def prev_filter_type
  @prev_filter_type
end

Instance Method Details

#change_filter(new_filter) ⇒ Object Also known as: filter_type=

Replace the filter type with new_filter, and it will compute the filters again.

This operation will be a legal way to change filter types.



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# File 'lib/pnglitch/scanline.rb', line 85

def change_filter new_filter
  @prev_filter_type = @filter_type
  @filter_type = new_filter
  self.save
end

#data ⇒ Object

Returns data of the scanline.



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# File 'lib/pnglitch/scanline.rb', line 37

def data
  if @data.nil?
    pos = @io.pos
    @io.pos = @start_at + 1
    @data = @io.read @data_size
    @io.pos = pos
  end
  @data
end

#graft(new_filter) ⇒ Object

Replace the filter type with new_filter, and it will not compute the filters again.

It means the scanline might get wrong filter type. It will be the efficient way to break the PNG image.



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# File 'lib/pnglitch/scanline.rb', line 75

def graft new_filter
  @filter_type = new_filter
  save
end

#gsub!(pattern, replacement) ⇒ Object

Replaces data with given Regexp pattern and replacement.

It is same as scanline.replace_data(scanline.data.gsub(pattern, replacement)). When the data size has changed, the data will be chopped or padded with null string in original size.



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# File 'lib/pnglitch/scanline.rb', line 54

def gsub! pattern, replacement
  self.replace_data self.data.gsub(pattern, replacement)
end

#register_filter_decoder(decoder = nil, &block) ⇒ Object

Registers a custom filter function to decode data.

With this operation, it will be able to change filter decoding behavior despite the specified filter type value. It takes a Proc object or a block.



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# File 'lib/pnglitch/scanline.rb', line 112

def register_filter_decoder decoder = nil, &block
  if !decoder.nil? && decoder.is_a?(Proc)
    @filter_codec[:decoder] = decoder
  elsif block_given?
    @filter_codec[:decoder] = block
  end
  save
end

#register_filter_encoder(encoder = nil, &block) ⇒ Object

Registers a custom filter function to encode data.

With this operation, it will be able to change filter encoding behavior despite the specified filter type value. It takes a Proc object or a block.



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# File 'lib/pnglitch/scanline.rb', line 97

def register_filter_encoder encoder = nil, &block
  if !encoder.nil? && encoder.is_a?(Proc)
    @filter_codec[:encoder] = encoder
  elsif block_given?
    @filter_codec[:encoder] = block
  end
  save
end

#replace_data(new_data) ⇒ Object Also known as: data=

Replace the data with new_data.

When its size has changed, the data will be chopped or padded with null string in original size.



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# File 'lib/pnglitch/scanline.rb', line 64

def replace_data new_data
  @data = new_data
  save
end

#save ⇒ Object

Save the changes.



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# File 'lib/pnglitch/scanline.rb', line 124

def save
  pos = @io.pos
  @io.pos = @start_at
  @io << [Filter.guess(@filter_type)].pack('C')
  @io << self.data.slice(0, @data_size).ljust(@data_size, "\0")
  @io.pos = pos
  @callback.call(self) unless @callback.nil?
  self
end