Class: Tiff::Tag

Inherits:
Object
  • Object
show all
Defined in:
lib/tiff/tag.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(name, id, type, map = nil) ⇒ Tag

Creates a new tag.

  • name: A rubyish name for the tag. Displayed to users for exceptions.

  • id: The value for this tag as defined by ‘tiff.h`

  • type: The FFI type of the tag

  • map: A hash of ruby to FFI values (optional)

Examples:

width = Tag.new(:width, 256, :uint)
metric = Tag.new(:photometric, 262, :ushort, {
  min_is_white: 0,
  min_is_black: 1
})



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# File 'lib/tiff/tag.rb', line 33

def initialize(name, id, type, map = nil)
  @name = name
  @id = id
  @type = type
  @map = map
end

Instance Attribute Details

#id ⇒ Object

The value for this tag as defined by ‘tiff.h`



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# File 'lib/tiff/tag.rb', line 8

def id
  @id
end

#map ⇒ Object

A hash of ruby to FFI values for serialization and deserialization.



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# File 'lib/tiff/tag.rb', line 16

def map
  @map
end

#name ⇒ Object

The name of this tag



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# File 'lib/tiff/tag.rb', line 5

def name
  @name
end

#type ⇒ Object

The FFI type for this tag. See ‘man TIFFSetField` for the types of each field, and `github.com/ffi/ffi/wiki/Types` for it’s corresponding value in ruby.



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# File 'lib/tiff/tag.rb', line 13

def type
  @type
end

Instance Method Details

#deserialize(pointer) ⇒ Object

Returns the deserialized value from the provided FFI::MemoryPointer.

If a map was provided for the tag, it will return the ruby value if it exists. If the mapping isn’t found, it will return the raw value.



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# File 'lib/tiff/tag.rb', line 57

def deserialize(pointer)
  case type
    when :string
      string = pointer.read_pointer()
      return string.null? ? nil : string.read_string()

    else
      value = pointer.send :"read_#{type}"
      value = map.invert[value] if map && map.has_value?(value)
      value
  end
end

#serialize(value) ⇒ Object

Returns the value for serialization. If the tag does not have a map defined, this simply returns the value provided.

If a map was provided for the tag, it will return the value for the mapping. If the mapping isn’t found, it will raise an exception.



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# File 'lib/tiff/tag.rb', line 45

def serialize(value)
  return value unless map

  map.fetch value do
    raise KeyError, "Tag #{name.inspect} does not support value #{value.inspect}. Defined values: #{map.keys}"
  end
end