class ChunkyPNG::Chunk::Physical

The Physical (pHYs) chunk specifies the intended pixel size or aspect ratio for display of the image.

www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.pHYs

Constants

INCHES_PER_METER

Attributes

ppux[RW]
ppuy[RW]
unit[RW]

Public Class Methods

new(ppux, ppuy, unit = :unknown) click to toggle source
Calls superclass method ChunkyPNG::Chunk::Base.new
# File lib/chunky_png/chunk.rb, line 329
def initialize(ppux, ppuy, unit = :unknown)
  raise ArgumentError, 'unit must be either :meters or :unknown' unless [:meters, :unknown].member?(unit)
  super('pHYs')
  @ppux, @ppuy, @unit = ppux, ppuy, unit
end
read(type, content) click to toggle source
# File lib/chunky_png/chunk.rb, line 345
def self.read(type, content)
  ppux, ppuy, unit = content.unpack('NNC')
  unit = unit == 1 ? :meters : :unknown
  new(ppux, ppuy, unit)
end

Public Instance Methods

content() click to toggle source

Assembles the content to write to the stream for this chunk. @return [String] The binary content that should be written to the datastream.

# File lib/chunky_png/chunk.rb, line 353
def content
  [ppux, ppuy, unit == :meters ? 1 : 0].pack('NNC')
end
dpix() click to toggle source
# File lib/chunky_png/chunk.rb, line 335
def dpix
  raise ChunkyPNG::UnitsUnknown, 'the PNG specifies its physical aspect ratio, but does not specify the units of its pixels\ physical dimensions' unless unit == :meters
  ppux * INCHES_PER_METER
end
dpiy() click to toggle source
# File lib/chunky_png/chunk.rb, line 340
def dpiy
  raise ChunkyPNG::UnitsUnknown, 'the PNG specifies its physical aspect ratio, but does not specify the units of its pixels\ physical dimensions' unless unit == :meters
  ppuy * INCHES_PER_METER
end