Class: PDF::Reader::PageState

Inherits:
Object
  • Object
show all
Defined in:
lib/pdf/reader/page_state.rb

Overview

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.

Constant Summary collapse

DEFAULT_GRAPHICS_STATE = 
{
  :char_spacing   => 0,
  :word_spacing   => 0,
  :h_scaling      => 1.0,
  :text_leading   => 0,
  :text_font      => nil,
  :text_font_size => 0,
  :text_mode      => 0,
  :text_rise      => 0,
  :text_knockout  => 0
}

Instance Method Summary collapse

Constructor Details

#initialize(page) ⇒ PageState

starting a new page



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# File 'lib/pdf/reader/page_state.rb', line 26

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

Instance Method Details

#begin_text_object ⇒ Object

Text Object Operators



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# File 'lib/pdf/reader/page_state.rb', line 90

def begin_text_object
  @text_matrix      = identity_matrix
  @text_line_matrix = identity_matrix
  @font_size = nil
end

#clone_state ⇒ Object

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.



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# File 'lib/pdf/reader/page_state.rb', line 291

def clone_state
  if @stack.empty?
    {}
  else
    Marshal.load Marshal.dump(@stack.last)
  end
end

#concatenate_matrix(a, b, c, d, e, f) ⇒ Object

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.



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# File 'lib/pdf/reader/page_state.rb', line 72

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) ⇒ Object

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



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# File 'lib/pdf/reader/page_state.rb', line 227

def ctm_transform(x, y)
  [
    (ctm.a * x) + (ctm.c * y) + (ctm.e),
    (ctm.b * x) + (ctm.d * y) + (ctm.f)
  ]
end

#current_font ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 252

def current_font
  find_font(state[:text_font])
end

#end_text_object ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 96

def end_text_object
  # don't need to do anything
end

#find_color_space(label) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 263

def find_color_space(label)
  dict = @cs_stack.detect { |colorspaces|
    colorspaces.has_key?(label)
  }
  dict ? dict[label] : nil
end

#find_font(label) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 256

def find_font(label)
  dict = @font_stack.detect { |fonts|
    fonts.has_key?(label)
  }
  dict ? dict[label] : nil
end

#find_xobject(label) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 270

def find_xobject(label)
  dict = @xobject_stack.detect { |xobjects|
    xobjects.has_key?(label)
  }
  dict ? dict[label] : nil
end

#font_size ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 117

def font_size
  @font_size ||= begin
                   _, zero = trm_transform(0,0)
                   _, one  = trm_transform(1,1)
                   (zero - one).abs
                 end
end

#invoke_xobject(label) ⇒ Object

XObjects

Raises:



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# File 'lib/pdf/reader/page_state.rb', line 198

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) ⇒ Object

Text Positioning Operators



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# File 'lib/pdf/reader/page_state.rb', line 145

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) ⇒ Object

TD



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# File 'lib/pdf/reader/page_state.rb', line 158

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) ⇒ Object

‘



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# File 'lib/pdf/reader/page_state.rb', line 185

def move_to_next_line_and_show_text(str) # '
  move_to_start_of_next_line
end

#move_to_start_of_next_line ⇒ Object

T*



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# File 'lib/pdf/reader/page_state.rb', line 173

def move_to_start_of_next_line # T*
  move_text_position(0, -state[:text_leading])
end

#process_glyph_displacement(w0, tj, word_boundary) ⇒ Object

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



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# File 'lib/pdf/reader/page_state.rb', line 321

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 ⇒ Object

Restore the state to the previous value on the stack.



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# File 'lib/pdf/reader/page_state.rb', line 57

def restore_graphics_state
  @stack.pop
end

#save_graphics_state ⇒ Object

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.



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# File 'lib/pdf/reader/page_state.rb', line 51

def save_graphics_state
  @stack.push clone_state
end

#set_character_spacing(char_spacing) ⇒ Object

Text State Operators



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# File 'lib/pdf/reader/page_state.rb', line 104

def set_character_spacing(char_spacing)
  state[:char_spacing] = char_spacing
end

#set_horizontal_text_scaling(h_scaling) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 108

def set_horizontal_text_scaling(h_scaling)
  state[:h_scaling] = h_scaling / 100.0
end

#set_spacing_next_line_show_text(aw, ac, string) ⇒ Object

“



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# File 'lib/pdf/reader/page_state.rb', line 189

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) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 112

def set_text_font_and_size(label, size)
  state[:text_font]      = label
  state[:text_font_size] = size
end

#set_text_leading(leading) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 125

def set_text_leading(leading)
  state[:text_leading] = leading
end

#set_text_matrix_and_text_line_matrix(a, b, c, d, e, f) ⇒ Object

Tm



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# File 'lib/pdf/reader/page_state.rb', line 163

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) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 129

def set_text_rendering_mode(mode)
  state[:text_mode] = mode
end

#set_text_rise(rise) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 133

def set_text_rise(rise)
  state[:text_rise] = rise
end

#set_word_spacing(word_spacing) ⇒ Object 



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# File 'lib/pdf/reader/page_state.rb', line 137

def set_word_spacing(word_spacing)
  state[:word_spacing] = word_spacing
end

#show_text_with_positioning(params) ⇒ Object

Text Showing Operators



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# File 'lib/pdf/reader/page_state.rb', line 181

def show_text_with_positioning(params) # TJ
  # TODO record position changes in state here
end

#stack_depth ⇒ Object

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.



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# File 'lib/pdf/reader/page_state.rb', line 281

def stack_depth
  @stack.size
end

#trm_transform(x, y) ⇒ Object

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



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# File 'lib/pdf/reader/page_state.rb', line 240

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