class PDF::Reader::PageState

encapsulates logic for tracking graphics state as the instructions for a single page are processed. Most of the public methods correspond directly to PDF operators.

Constants

DEFAULT_GRAPHICS_STATE

Public Class Methods

new(page) click to toggle source

starting a new page

: (untyped) -> void

# File lib/pdf/reader/page_state.rb, line 27
def initialize(page)
  @page          = page
  @cache         = page.cache
  @objects       = page.objects
  @font_stack    = [build_fonts(page.fonts)]
  @xobject_stack = [page.xobjects]
  @cs_stack      = [page.color_spaces]
  @stack         = [DEFAULT_GRAPHICS_STATE.dup]
  state[:ctm]  = identity_matrix

  # These are only valid when inside a `BT` block and we re-initialize them on each
  # `BT`. However, we need the instance variables set so PDFs with the text operators
  # out order don't trigger NoMethodError when these are nil
  @text_matrix      = identity_matrix
  @text_line_matrix = identity_matrix
end

Public Instance Methods

begin_text_object() click to toggle source

Text Object Operators

# File lib/pdf/reader/page_state.rb, line 93
def begin_text_object
  @text_matrix      = identity_matrix
  @text_line_matrix = identity_matrix
  @font_size = nil
end

clone_state() click to toggle source

This returns a deep clone of the current state, ensuring changes are keep separate from earlier states.

Marshal is used to round-trip the state through a string to easily perform the deep clone. Kinda hacky, but effective.

# File lib/pdf/reader/page_state.rb, line 294
def clone_state
  if @stack.empty?
    {}
  else
    Marshal.load Marshal.dump(@stack.last)
  end
end

concatenate_matrix(a, b, c, d, e, f) click to toggle source

update the current transformation matrix.

If the CTM is currently undefined, just store the new values.

If there’s an existing CTM, then multiply the existing matrix with the new matrix to form the updated matrix.

# File lib/pdf/reader/page_state.rb, line 75
def concatenate_matrix(a, b, c, d, e, f)
  if state[:ctm]
    ctm = state[:ctm]
    state[:ctm] = TransformationMatrix.new(a,b,c,d,e,f).multiply!(
      ctm.a, ctm.b,
      ctm.c, ctm.d,
      ctm.e, ctm.f
    )
  else
    state[:ctm] = TransformationMatrix.new(a,b,c,d,e,f)
  end
  @text_rendering_matrix = nil # invalidate cached value
end

ctm_transform(x, y) click to toggle source

transform x and y co-ordinates from the current user space to the underlying device space.

# File lib/pdf/reader/page_state.rb, line 230
def ctm_transform(x, y)
  [
    (ctm.a * x) + (ctm.c * y) + (ctm.e),
    (ctm.b * x) + (ctm.d * y) + (ctm.f)
  ]
end

current_font() click to toggle source

# File lib/pdf/reader/page_state.rb, line 255
def current_font
  find_font(state[:text_font])
end

end_text_object() click to toggle source

# File lib/pdf/reader/page_state.rb, line 99
def end_text_object
  # don't need to do anything
end

find_color_space(label) click to toggle source

# File lib/pdf/reader/page_state.rb, line 266
def find_color_space(label)
  dict = @cs_stack.detect { |colorspaces|
    colorspaces.has_key?(label)
  }
  dict ? dict[label] : nil
end

find_font(label) click to toggle source

# File lib/pdf/reader/page_state.rb, line 259
def find_font(label)
  dict = @font_stack.detect { |fonts|
    fonts.has_key?(label)
  }
  dict ? dict[label] : nil
end

find_xobject(label) click to toggle source

# File lib/pdf/reader/page_state.rb, line 273
def find_xobject(label)
  dict = @xobject_stack.detect { |xobjects|
    xobjects.has_key?(label)
  }
  dict ? dict[label] : nil
end

font_size() click to toggle source

# File lib/pdf/reader/page_state.rb, line 120
def font_size
  @font_size ||= begin
                   _, zero = trm_transform(0,0)
                   _, one  = trm_transform(1,1)
                   (zero - one).abs.round(10)
                 end
end

invoke_xobject(label) { |form| ... } click to toggle source

XObjects

# File lib/pdf/reader/page_state.rb, line 201
def invoke_xobject(label)
  save_graphics_state
  xobject = find_xobject(label)

  raise MalformedPDFError, "XObject #{label} not found" if xobject.nil?
  matrix = xobject.hash[:Matrix]
  concatenate_matrix(*matrix) if matrix

  if xobject.hash[:Subtype] == :Form
    form = PDF::Reader::FormXObject.new(@page, xobject, :cache => @cache)
    @font_stack.unshift(form.font_objects)
    @xobject_stack.unshift(form.xobjects)
    yield form if block_given?
    @font_stack.shift
    @xobject_stack.shift
  else
    yield xobject if block_given?
  end

  restore_graphics_state
end

move_text_position(x, y) click to toggle source

Text Positioning Operators

# File lib/pdf/reader/page_state.rb, line 148
def move_text_position(x, y) # Td
  temp = TransformationMatrix.new(1, 0,
                                  0, 1,
                                  x, y)
  @text_line_matrix = temp.multiply!(
    @text_line_matrix.a, @text_line_matrix.b,
    @text_line_matrix.c, @text_line_matrix.d,
    @text_line_matrix.e, @text_line_matrix.f
  )
  @text_matrix = @text_line_matrix.dup
  @font_size = @text_rendering_matrix = nil # invalidate cached value
end

move_text_position_and_set_leading(x, y) click to toggle source

# File lib/pdf/reader/page_state.rb, line 161
def move_text_position_and_set_leading(x, y) # TD
  set_text_leading(-1 * y)
  move_text_position(x, y)
end

move_to_next_line_and_show_text(str) click to toggle source

# File lib/pdf/reader/page_state.rb, line 188
def move_to_next_line_and_show_text(str) # '
  move_to_start_of_next_line
end

move_to_start_of_next_line() click to toggle source

# File lib/pdf/reader/page_state.rb, line 176
def move_to_start_of_next_line # T*
  move_text_position(0, -state[:text_leading])
end

process_glyph_displacement(w0, tj, word_boundary) click to toggle source

after each glyph is painted onto the page the text matrix must be modified. There’s no defined operator for this, but depending on the use case some receivers may need to mutate the state with this while walking a page.

NOTE: some of the variable names in this method are obscure because

they mirror variable names from the PDF spec

NOTE: see Section 9.4.4, PDF 32000-1:2008, pp 252

Arguments:

w0 - the glyph width in *text space*. This generally means the width

in glyph space should be divded by 1000 before being passed to
this function

tj - any kerning that should be applied to the text matrix before the

following glyph is painted. This is usually the numeric arguments
in the array passed to a TJ operator

word_boundary - a boolean indicating if a word boundary was just

reached. Depending on the current state extra space
may need to be added

# File lib/pdf/reader/page_state.rb, line 324
def process_glyph_displacement(w0, tj, word_boundary)
  fs = state[:text_font_size]
  tc = state[:char_spacing]
  if word_boundary
    tw = state[:word_spacing]
  else
    tw = 0
  end
  th = state[:h_scaling]
  # optimise the common path to reduce Float allocations
  if th == 1 && tj == 0 && tc == 0 && tw == 0
    tx = w0 * fs
  elsif tj != 0
    # don't apply spacing to TJ displacement
    tx = (w0 - (tj/1000.0)) * fs * th
  else
    # apply horizontal scaling to spacing values but not font size
    tx = ((w0 * fs) + tc + tw) * th
  end
  # TODO: support ty > 0
  ty = 0
  temp = TransformationMatrix.new(1, 0,
                                  0, 1,
                                  tx, ty)
  @text_matrix = temp.multiply!(
    @text_matrix.a, @text_matrix.b,
    @text_matrix.c, @text_matrix.d,
    @text_matrix.e, @text_matrix.f
  )
  @font_size = @text_rendering_matrix = nil # invalidate cached value
end

restore_graphics_state() click to toggle source

Restore the state to the previous value on the stack.

: () -> untyped

# File lib/pdf/reader/page_state.rb, line 60
def restore_graphics_state
  @stack.pop
end

save_graphics_state() click to toggle source

Clones the current graphics state and push it onto the top of the stack.
Any changes that are subsequently made to the state can then by reversed
by calling restore_graphics_state.

: () -> untyped

# File lib/pdf/reader/page_state.rb, line 53
def save_graphics_state
  @stack.push clone_state
end

set_character_spacing(char_spacing) click to toggle source

Text State Operators

# File lib/pdf/reader/page_state.rb, line 107
def set_character_spacing(char_spacing)
  state[:char_spacing] = char_spacing
end

set_horizontal_text_scaling(h_scaling) click to toggle source

# File lib/pdf/reader/page_state.rb, line 111
def set_horizontal_text_scaling(h_scaling)
  state[:h_scaling] = h_scaling / 100.0
end

set_spacing_next_line_show_text(aw, ac, string) click to toggle source

# File lib/pdf/reader/page_state.rb, line 192
def set_spacing_next_line_show_text(aw, ac, string) # "
  set_word_spacing(aw)
  set_character_spacing(ac)
  move_to_next_line_and_show_text(string)
end

set_text_font_and_size(label, size) click to toggle source

# File lib/pdf/reader/page_state.rb, line 115
def set_text_font_and_size(label, size)
  state[:text_font]      = label
  state[:text_font_size] = size
end

set_text_leading(leading) click to toggle source

# File lib/pdf/reader/page_state.rb, line 128
def set_text_leading(leading)
  state[:text_leading] = leading
end

set_text_matrix_and_text_line_matrix(a, b, c, d, e, f) click to toggle source

# File lib/pdf/reader/page_state.rb, line 166
def set_text_matrix_and_text_line_matrix(a, b, c, d, e, f) # Tm
  @text_matrix = TransformationMatrix.new(
    a, b,
    c, d,
    e, f
  )
  @text_line_matrix = @text_matrix.dup
  @font_size = @text_rendering_matrix = nil # invalidate cached value
end

set_text_rendering_mode(mode) click to toggle source

# File lib/pdf/reader/page_state.rb, line 132
def set_text_rendering_mode(mode)
  state[:text_mode] = mode
end

set_text_rise(rise) click to toggle source

# File lib/pdf/reader/page_state.rb, line 136
def set_text_rise(rise)
  state[:text_rise] = rise
end

set_word_spacing(word_spacing) click to toggle source

# File lib/pdf/reader/page_state.rb, line 140
def set_word_spacing(word_spacing)
  state[:word_spacing] = word_spacing
end

show_text_with_positioning(params) click to toggle source

Text Showing Operators

# File lib/pdf/reader/page_state.rb, line 184
def show_text_with_positioning(params) # TJ
  # TODO record position changes in state here
end

stack_depth() click to toggle source

when save_graphics_state is called, we need to push a new copy of the current state onto the stack. That way any modifications to the state will be undone once restore_graphics_state is called.

# File lib/pdf/reader/page_state.rb, line 284
def stack_depth
  @stack.size
end

trm_transform(x, y) click to toggle source

transform x and y co-ordinates from the current text space to the underlying device space.

transforming (0,0) is a really common case, so optimise for it to avoid unnecessary object allocations

# File lib/pdf/reader/page_state.rb, line 243
def trm_transform(x, y)
  trm = text_rendering_matrix
  if x == 0 && y == 0
    [trm.e, trm.f]
  else
    [
      (trm.a * x) + (trm.c * y) + (trm.e),
      (trm.b * x) + (trm.d * y) + (trm.f)
    ]
  end
end

Private Instance Methods

build_fonts(raw_fonts) click to toggle source

wrap the raw PDF Font objects in handy ruby Font objects.

# File lib/pdf/reader/page_state.rb, line 394
def build_fonts(raw_fonts)
  wrapped_fonts = raw_fonts.map { |label, font|
    [label, PDF::Reader::Font.new(@objects, @objects.deref_hash(font) || {})]
  }

  ::Hash[wrapped_fonts]
end

ctm() click to toggle source

return the current transformation matrix

# File lib/pdf/reader/page_state.rb, line 384
def ctm
  state[:ctm]
end

identity_matrix() click to toggle source

This class uses 3x3 matrices to represent geometric transformations These matrices are represented by arrays with 9 elements The array [a,b,c,d,e,f,g,h,i] would represent a matrix like:

a b c
d e f
g h i

# File lib/pdf/reader/page_state.rb, line 413
def identity_matrix
  TransformationMatrix.new(1, 0,
                           0, 1,
                           0, 0)
end

state() click to toggle source

# File lib/pdf/reader/page_state.rb, line 388
def state
  @stack.last
end

text_rendering_matrix() click to toggle source

used for many and varied text positioning calculations. We potentially need to access the results of this method many times when working with text, so memoize it

# File lib/pdf/reader/page_state.rb, line 362
def text_rendering_matrix
  @text_rendering_matrix ||= begin
    state_matrix = TransformationMatrix.new(
      state[:text_font_size] * state[:h_scaling], 0,
      0, state[:text_font_size],
      0, state[:text_rise]
    )
    state_matrix.multiply!(
      @text_matrix.a, @text_matrix.b,
      @text_matrix.c, @text_matrix.d,
      @text_matrix.e, @text_matrix.f
    )
    state_matrix.multiply!(
      ctm.a, ctm.b,
      ctm.c, ctm.d,
      ctm.e, ctm.f
    )
  end
end