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Converting a persistent object into a memory block

Other usage issuesThu, 07/01/2004 - 14:484 replies

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QuestionAuthor

Hallo,
I am working on a plugin for the rendering software Realsoft3D, this plugin introduces the modeling features of OpenCASCADE in that host program. First results are encouraging, see for instance..
http://www.deltaknowledge.com/gallery/thumbnails.php?album=5
My problem is that I have to implement the serialization of my 'shape' objects for the Realsoft3D binary files, that is I
need to save (for example) a TopoDS_Shape into an already opened
binary file. The same for loading. Then, it looks a bit like
the CArchive mechanism for MSFC technology (but I do not use MSFC).
Well, I cannot use the BRepTool::Write function because it uses an
ascii file (it would mix it with the stream containing other
Realsoft3D binary info.. I do not know if this is a good way to go..)
So I thought that a basic method could be to convert the
transient object to persistent object, then to save the persistent
object byte-by-byte on file. Is this possible? And how?

best regards,

Discussion

4 archived replies

Posts are displayed in their archived order.

01Commenter-1

Hello Alessandro,
we did in fact use a similar approach to the BRepTool::Write method to serialize a TopoDS_Shape. What we did was to implement new class based on BRepTools_ShapeSet, GeomTools_Curve2dSet, GeomTools_CurveSet , GeomTools_SurfaceSet TopTools_LocationSet and TopTools_ShapeSet and we make sure to remove anything ASCII related to be able to used in with a binary stream. Then, to read a shape from a stream at a the current location we just do:

QDataStream is;
TopoDS_Shape a;
BRep_Builder aBuilder;
QBRepTools_ShapeSet SS(aBuilder);
SS.Read(is);
SS.Read(a,is);

to write it we do:

QDataStream is;
TopoDS_Shape a=...;

// we do a triangulation clean before writing to save some space
BRepTools::Clean(a);

QBRepTools_ShapeSet SS;
SS.Add(a);
SS.Write(os);
SS.Write(a,os);

We have been doing this for 5 years.
Good Luck,
Commenter-1.

02Commenter-2

Thank you Francois!

In fact I suspected that a posible way to go was
to rewrite the BRepTools_ShapeSet class (and the other
classes you told me), but I hoped there was a simplier
method...
For the moment, I found an easy workaround: on serialization

03Commenter-2

Thank you Francois!

In fact I suspected that a posible way to go was
to rewrite the BRepTools_ShapeSet class (and the other
classes you told me), but I hoped there was a simplier
method...
For the moment, I found an easy workaround: when
serializing my shape on disk, I simply save a
'temporary' .brep file on HD using the OpenCASCADE
tool, then I read it byte-by-byte as raw data,
and I store it 'embedded' in my custom binary file
using my file functions. The temporary file is deleted
automatically. Viceversa for loading from disk.

Of course this is a 'dirty' workaround, since it is
not very fast (nor memory-efficient), and it still passes
through ascii conversions of floatingpoint numbers (precision
is affected?). But enough for now.

Thank you very much for your help!

Commenter-2

04Commenter-3

Hello Francois,
I'm having the same problem but I saw that there's something done with the Storage_Schema and his driver FSD_BinaryFile, but it didn't seems to be finish...did you tried that?
And for the solution you did, how much time did takes you to rewrite all those saves functions??

Thank you,
David.