[poppler] Access to Poppler internal C++ API by GDAL

[jose.aliste at gmail.com]

Hi,
the internal c++ API is not intended for use by external applications, only
by frontends. So, if you want a stable API, you should be using either of
the frontends. There is a cpp frontend that should be fare more stable.

Regards


On Sun, Sep 10, 2017 at 10:41 AM, Even Rouault <even.rouault at spatialys.com>
wrote:

> Hi,
>
>
>
> I'm one of the developper of the GDAL library (http://gdal.org) that
> reads various raster & vector formats, mostly geospatial, including PDF and
> its georeferencing extensions (either expressed wtih Adobe Supplement to
> ISO 32000 or with Open Geospatial Consortium Best Practice:
>
> https://portal.opengeospatial.org/files/?artifact_id=40537 )
>
>
>
> Currently we use the Poppler internal C++ API and regularly must adjust
> for changes in it. Recently we had to do adjustments to accomodate for
> Poppler 0.58 changes. Supporting multiple Poppler versions begin to make
> our code ugly. So I and packagers from Linux distribution are wondering if
> there would be a way to access a more stable C++ API
>
>
>
> Besides rendering as image, we need really low-level access to PDF
> objects, to be able to parse georeferencing objects, retrieve layers, turn
> on/off OCG, or even access streams to decode drawing instructions so as to
> build vector objects
>
>
>
> I've tried to summarize below our current use of Poppler C++ API. I
> probably missed a few calls, but you should get the overall picture:
>
> - Object class: getType(), getTypeName(), getBool(), getInt(), getReal(),
> getString(), getName(), getStream(), getArray()
>
> - Dict class: lookupNF(), lookup(), getLength(), getKey()
>
> - Array class: getLength(), getNF(), get()
>
> - Stream class: getDict(), reset(), getChar(), fillGooString()
>
> - Catalog class: getPage(), getPageRef(), readMetadata()
>
> - GooString: getCString(), getLength()
>
> - Ref class: access to num and gen
>
> - PDFDoc class: isOk(), displayPageSlice(), getCatalog(),
> getOptContentConfig(), getNumPages(), getDocInfo(), getErrorCode(), str
> private member(accessed through a ugly "#define private public" before
> including poppler! we need to access it to be able to delete it with our
> heap since we allocated a stream object provided to PDFDoc() constructor.
> this is to avoid potential problems on Windows with cross-heap issues)
>
> - Page class: isOk(), pageObj private member (accessed through a ugly
> "#define private public" before including poppler!), getMediaBox()
>
> - OCGs class: isOk(), getOCGs()
>
> - GooList class: getLength(), get()
>
> - OptionalContentGroup class: setState()
>
> - SplashBitmap class: getBitmap(), getWidth(), getHeigh(), getDataPtr(),
> getAlphaPtr(), getAlphaRowSize(), getRowSize()
>
> - SplashOutputDev class: we subclass this class and override all/most
> virtual methods to be able to turn on/off rendering of various elements as
> we offer options to render selectively vector, raster and/or text elements
> (so basically just a conditional test to decide whether to return as a
> no-op or call the base implementation)
>
> - BaseStream class: we subclass this class to use GDAL own I/O abstraction
> layer (which beyond regular files can read in .zip files, in-memory files,
> files available through HTTP, etc...). So we implement copy(),
> makeSubStream(), getPos(), getStart(), setPos(), moveStart(), getKind(),
> getFileName(), getChar(), makeSubStream(), lookChar(), reset(),
> unfilteredReset(), close(), hasGetChars(), getChars()
>
> - GlobalParams class: setPrintCommands()
>
> - setErrorCallback() function
>
>
>
> If you want to glance at the code, the most relevant files are:
>
> https://github.com/OSGeo/gdal/blob/trunk/gdal/frmts/pdf/pdfobject.cpp
>
> https://github.com/OSGeo/gdal/blob/trunk/gdal/frmts/pdf/pdfio.cpp
>
> https://github.com/OSGeo/gdal/blob/trunk/gdal/frmts/pdf/pdfdataset.cpp
>
>
>
> I'm not clear if that would be feasible for Poppler to provide a more
> stable API for our use. At least, this makes you aware of external users of
> this API.
>
>
>
> Best regards,
>
>
>
> Even
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>
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>
>
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