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Ruby / Guides / Graphics state

Graphics state in Ruby

To traverse the list of changes in the graphics state.

gs_itr = reader.GetChangesIterator
while gs_itr.HasNext do
  case gs_itr.Current
  when GState::E_transform
    # Get transform matrix for this element. Unlike path.GetCTM 
    # that return full transformation matrix gs.GetTransform return 
    # only the transformation matrix that was installed for this element.
    # gs.GetTransform
  when GState::E_line_width
    # gs.GetLineWidth
  when GState::E_line_cap
    # gs.GetLineCap
  when GState::E_line_join
    # gs.GetLineJoin
  when GState::E_miter_limit
    # gs.GetMiterLimit
  when GState::E_dash_pattern
    # dashes = gs.GetDashes
    # gs.GetPhase

PDF Data Extraction (Images, Text, Paths)
Full code sample which illustrates how to extract data, do color conversion, image normalization, and how to process changes in the graphics state.

About graphics state

After reading an Element using ElementReader.Next(), it is possible to access all graphical attributes of the Element through its graphics state. Some applications are more interested in changes in the graphics state than attribute values. For example, a transition from one Element to another may not involve changes in the graphics state. Or, perhaps, there may be changes only to a couple of attributes. In these cases, it isn't efficient to make memberwise comparisons between the old and current graphics states.

To make this easier and more efficient, Apryse SDK offers an API to enumerate the list of changes between subsequent Elements.

It's also possible to query ElementReader for changes to a specific attribute:

if (reader.IsChanged(GState::E_line_width))
   # line width was changed.

Note that the list of modified attributes is accumulated when calling ElementReader.Next(). To clear the list of modified attributes use ElementReader.ClearChangeList() method. A call to ClearChangeList() serves as a marker in the display list from which further changes in the graphics state are tracked.

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