Module: Prawn::SoftMask

Included in:
Document
Defined in:
lib/prawn/soft_mask.rb

Overview

The Prawn::SoftMask module is used to create arbitrary transparency in document. Using a soft mask allows creating more visually rich documents.

You must group soft mask and graphics it's applied to under save_graphics_state because soft mask is a part of graphic state in PDF.

Example:

pdf.save_graphics_state do
  pdf.soft_mask do
    pdf.fill_color "444444"
    pdf.fill_polygon [0, 40], [60, 10], [120, 40], [60, 68]
  end
  pdf.fill_color '000000'
  pdf.fill_rectangle [0, 50], 120, 68
end

Stable API collapse

Instance Method Details

#soft_mask(&block) ⇒ Object 



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# File 'lib/prawn/soft_mask.rb', line 30

def soft_mask(&block)
  renderer.min_version(1.4)

  group_attrs = ref!(
    Type: :Group,
    S: :Transparency,
    CS: :DeviceRGB,
    I: false,
    K: false
  )

  group = ref!(
    Type: :XObject,
    Subtype: :Form,
    BBox: state.page.dimensions,
    Group: group_attrs
  )

  state.page.stamp_stream(group, &block)

  mask = ref!(
    Type: :Mask,
    S: :Luminosity,
    G: group
  )

  g_state = ref!(
    Type: :ExtGState,
    SMask: mask,

    AIS: false,
    BM: :Normal,
    OP: false,
    op: false,
    OPM: 1,
    SA: true
  )

  registry_key = {
    bbox: state.page.dimensions,
    mask: [group.stream.filters.normalized, group.stream.filtered_stream],
    page: state.page_count
  }.hash

  if soft_mask_registry[registry_key]
    renderer.add_content "/#{soft_mask_registry[registry_key]} gs"
  else
    masks = page.resources[:ExtGState] ||= {}
    id = masks.empty? ? 'GS1' : masks.keys.max.succ
    masks[id] = g_state

    soft_mask_registry[registry_key] = id

    renderer.add_content "/#{id} gs"
  end
end