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/** \page tutorial_08 Using IO::Options

This example shows:

- How to control the behaviour of \c Mesh::IO::read_mesh(),
- How to control the behaviour of \c Mesh::IO::write_mesh().

The class \c OpenMesh::IO::Options can be used when reading/writing a
mesh. It controls the behaviour of the reader/writer modules by means
of enabled/disabled bits in a bitset. The class provides an interface
for enabling, disabling and verifying the bits in the set. We
distinguish between

-# mode bits - control binary reading/writing
 - Options::Binary
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 - Options::MSB
 - Options::LSB
 - Options::Swap (MSB|LSB)
-# property bits - controls which standard properties to read/write
 - Options::VertexNormal
 - Options::VertexTexCoord
 - Options::VertexColor
 - Options::FaceNormal
 - Options::FaceColor
 - Options::FaceTexCoord
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 - Options::ColorAlpha
 - Options::ColorFloat
 - Options::Custom
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These bits have different effects when reading or writing. The file
format itself is selected by the extension of the filename. 
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Please take into account, each mesh has to <b>request</b> the standard property <b>before loading</b> with the corresponding option.
For instance, if you enable Options::VertexNormal, your mesh has to request vertex normals. Otherwise, they will not be written into the mesh.
\note Face Tex Coords will not be saved as a property per face, but as a property per halfedge. Therefore, you have to request the "halfedge_texcoords2D" property

The OBJ-reader can also read information about the textures in the *.mtl file, if available.
These texture information (includes texturename and index) will be saved in the property of type:
\code OpenMesh::MPropHandleT< std::map< int, std::string > > \endcode
with the name:
\code "TextureMapping" \endcode
This property will be automatically created, if textures were found. There is no other option you have to define for reading texture information beside of the request of the property.\n
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Additionally, the OBJ loader writes the texture index per face, if the property "face_texture_index" is requested. The texture index is
the same index as the index written in the texture mapping. So, it is possible to get the name of the texture from a face via its texture index over the texture mapping property
to the texture name. But remember, you have to request the face texture index property first before loading the mesh.
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Below in the table you can see what options are suported by which reader/writer (it is possible that the data format can support more).
ASCII is not a real option and will be selected, if binary was not defined.

<CAPTION><EM>Reader/Writer Feature Support List</EM></CAPTION>
<TR><TH>OBJ<TD>x<TD> <TD> <TD> <TD> <TD>x<TD>x *)<TD>x<TD> <TD>x<TD>x<TD>x<TD><TD><TD> 
<TR><TH>OFF<TD>x<TD>x<TD> <TD>x<TD> <TD>x<TD>x<TD>x<TD> <TD> <TD>x<TD> <TD>x<TD>x<TD> 
<TR><TH>PLY<TD>x<TD>x<TD>x<TD>x<TD> <TD>x<TD>x<TD>x<TD> <TD> <TD> <TD> <TD>x<TD>x<TD>x **)
<TR><TH>OM<TD> <TD>x<TD>x<TD>x<TD>x<TD>x<TD>x<TD>x<TD><TD>x<TD>x<TD><TD><TD><TD>x (\ref tutorial_09 )
<TR><TH>VTK ***)<TD>x<TD><TD><TD><TD><TD><TD><TD><TD><TD><TD><TD><TD><TD><TD>

\*) can <i>read</i> the non-standard extension vertex colors (floats only): 
\li defined with vc (e.g. used by meshlab)
\li colors encoded in a vertex line (v followed by 6 values)

\**) only vertex and face properties with fundamental types. Take into account, that you don't have to request these custom properties before loading.
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\***) no reader exists
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The program does not more than providing a command line based
interface to select the option bits for reading/writing and to request
mesh properties. Hence illegal combinations are possible and will
result in a failure of the program. (The input file won't be damaged
in this case, but be careful where you put the ouput file!)

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<h5>Reading meshes</h5>

When reading a file the mode bits are used to give the reader an
advice or hint. Depending on the format we can help the reader to
interpret the data correctly. First of all we can tell it that the
file contains binary data.

\dontinclude 08-io_options/io_options.cc
\skipline ropt += IO::Options::Binary

Further on we can ask the reader two swap the byte-order.

\skipline ropt += IO::Options::Swap

(Both can be done via the command line with the options -b and -s,

By default the geometry and the topology is restored from the
file. The file might contain more, especially it could provide normals
or texture coordinates.  We can examine the property bits after
reading to find out what else is available:

\dontinclude 08-io_options/io_options.cc
\skipline ropt.check(IO::Options::VertexNormal)

If a property bit is set it does not mean, that it has been restored
as well.  The property must have been requested prior reading the
file. (The demo program offers the command line option \c -Xv[nct] and
\c -Xf[nc] to request vertex and face properties.)

<h5>Writing meshes</h5>

When writing the mesh the mode bits apparently control whether to use
the binary variant and the desired byte-ordering. For example, if we
choose binary mode and want to swap the byte order, we set

\skipline wopt += IO::Options::Binary
\skipline wopt += IO::Options::Swap

If the format does not specify the byte order the system byte order is
used. If the format does not support binary storage, the mode bits are

If the format supports storing additional information, which are
conform with the standard properties, we can use the property bits to
tell the writer what we would like to have stored. If we would like to
store the vertex normals we simply set

\skipline wopt += IO::Options::VertexNormal

Finally we can write the data to the file

\dontinclude 08-io_options/io_options.cc
\skipline write_mesh

The method returns false on error, which might have three different reasons:

-# the option is not supported by the choosen format
-# a selected standard property is not available
-# a 'system' error like
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   - could not open the file due to access rights
   - disk space exhausted during write
   - ...

The complete source looks like this:

\include 08-io_options/io_options.cc