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https://gitlab.kitware.com/vtk/vtk-m
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144 lines
5.2 KiB
ReStructuredText
144 lines
5.2 KiB
ReStructuredText
==============================
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File I/O
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==============================
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.. index::
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single: I/O
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single: file I/O
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Before |VTKm| can be used to process data, data need to be loaded into the
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system.
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|VTKm| comes with a basic file I/O package to get started developing very
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quickly.
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All the file I/O classes are declared under the ``vtkm::io`` namespace.
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.. didyouknow::
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Files are just one of many ways to get data in and out of |VTKm|.
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In later chapters we explore ways to define |VTKm| data structures of
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increasing power and complexity.
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In particular, :secref:`dataset:Building Data Sets` describes how to build |VTKm| data set objects and Section \ref{sec:ArrayHandle:Adapting} documents how to adapt data structures defined in other libraries to be used directly in |VTKm|.
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.. todo:: Add ArrayHandle section reference above.
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------------------------------
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Readers
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------------------------------
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.. index::
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single: file I/O; read
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single: read file
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All reader classes provided by |VTKm| are located in the ``vtkm::io``
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namespace.
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The general interface for each reader class is to accept a filename in the constructor and to provide a ``ReadDataSet`` method to load the data from disk.
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The data in the file are returned in a :class:`vtkm::cont::DataSet` object
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as described in :chapref:`dataset:Data Sets`, but it is sufficient to know that a ``DataSet`` can be passed among readers, writers, filters, and rendering units.
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Legacy VTK File Reader
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==============================
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Legacy VTK files are a simple open format for storing visualization data.
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These files typically have a :file:`.vtk` extension.
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Legacy VTK files are popular because they are simple to create and read and
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are consequently supported by a large number of tools.
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The format of legacy VTK files is well documented in *The VTK User's
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Guide* [as well as online](https://examples.vtk.org/site/VTKFileFormats/).
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Legacy VTK files can also be read and written with tools like ParaView and VisIt.
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Legacy VTK files can be read using the :class:`vtkm::io::VTKDataSetReader` class.
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.. doxygenclass:: vtkm::io::VTKDataSetReader
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:members:
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.. load-example:: VTKDataSetReader
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:file: GuideExampleIO.cxx
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:caption: Reading a legacy VTK file.
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Image Readers
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==============================
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|VTKm| provides classes to read images from some standard image formats.
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These readers will store the data in a :class:`vtkm::cont::DataSet` object with the colors stored as a named point field.
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The colors are read as 4-component RGBA vectors for each pixel.
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Each component in the pixel color is stored as a 32-bit float between 0 and 1.
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Portable Network Graphics (PNG) files can be read using the :class:`vtkm::io::ImageReaderPNG` class.
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.. doxygenclass:: vtkm::io::ImageReaderPNG
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:members:
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.. load-example:: ImageReaderPNG
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:file: GuideExampleIO.cxx
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:caption: Reading an image from a PNG file.
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Portable anymap (PNM) files can be read using the :class:`vtkm::io::ImageReaderPNM` class.
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.. doxygenclass:: vtkm::io::ImageReaderPNM
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:members:
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Like for PNG files, a :class:`vtkm::io::ImageReaderPNM` is constructed with the name of the file to read from.
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.. load-example:: ImageReaderPNM
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:file: GuideExampleIO.cxx
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:caption: Reading an image from a PNM file.
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------------------------------
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Writers
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------------------------------
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.. index::
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single: file I/O; write
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single: write file
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All writer classes provided by |VTKm| are located in the ``vtkm::io`` namespace.
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The general interface for each writer class is to accept a filename in the constructor and to provide a ``WriteDataSet`` method to save data to the disk.
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The ``WriteDataSet`` method takes a :class:`vtkm::cont::DataSet` object as an argument, which contains the data to write to the file.
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Legacy VTK File Writer
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==============================
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Legacy VTK files can be written using the :class:`vtkm::io::VTKDataSetWriter` class.
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.. doxygenclass:: vtkm::io::VTKDataSetWriter
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:members:
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.. doxygenenum:: vtkm::io::FileType
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.. load-example:: VTKDataSetWriter
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:file: GuideExampleIO.cxx
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:caption: Writing a legacy VTK file.
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Image Writers
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==============================
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|VTKm| provides classes to some standard image formats.
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These writers store data in a :class:`vtkm::cont::DataSet`.
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The data must be a 2D structure with the colors stored in a point field.
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(See :chapref:`dataset:Data Sets` for details on :class:`vtkm::cont::DataSet` objects.)
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Portable Network Graphics (PNG) files can be written using the :class:`vtkm::io::ImageWriterPNG` class.
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.. doxygenclass:: vtkm::io::ImageWriterPNG
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:members:
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By default, PNG files are written as RGBA colors using 8-bits for each component.
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You can change the format written using the :func:`vtkm::io::ImageWriterPNG::SetPixelDepth` method.
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This takes an item in the :enum:`vtkm::io::ImageWriterPNG::PixelDepth` enumeration.
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.. doxygenenum:: vtkm::io::ImageWriterBase::PixelDepth
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.. load-example:: ImageWriterPNG
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:file: GuideExampleIO.cxx
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:caption: Writing an image to a PNG file.
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Portable anymap (PNM) files can be written using the :class:`vtkm::io::ImageWriterPNM` class.
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.. doxygenclass:: vtkm::io::ImageWriterPNM
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:members:
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.. load-example:: ImageWriterPNM
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:file: GuideExampleIO.cxx
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:caption: Writing an image to a PNM file.
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