[Openexr-devel] Layer support in class ChannelList

[Florian Kainz]

In the next release of OpenEXR, class ChannelList will include minimal
support for layers using the "layername.channelname" naming convention.
See the excerpt from file ImfChannelList.h, below.

There is no standard way to store the order of layers or channels, or
how layers should be combined, since people don't seem to agree (yet)
on how this information should be represented.

Florian


-------------------


class ChannelList
{
  public:

    ...

    //-----------------------------------------------------------------
    // Support for image layers:
    //
    // In an image file with many channels it is sometimes useful to
    // group the channels into "layers", that is, into sets of channels
    // that logically belong together.  Grouping channels into layers
    // is done using a naming convention:  channel C in layer L is
    // called "L.C".
    //
    // For example, a computer graphic image may contain separate
    // R, G and B channels for light that originated at each of
    // several different virtual light sources.  The channels in
    // this image might be called "light1.R", "light1.G", "light1.B",
    // "light2.R", "light2.G", "light2.B", etc.
    //
    // Note that this naming convention allows layers to be nested;
    // for example, "light1.specular.R" identifies the "R" channel
    // in the "specular" sub-layer of layer "light1".
    //
    // Channel names that don't contain a "." or that contain a
    // "." only at the beginning or at the end are not considered
    // to be part of any layer.
    //
    // layers(lns)              sorts the channels in this ChannelList
    //                          into layers and stores the names of
    //                          all layers, sorted alphabetically,
    //                          into string set lns.
    //
    // channelsInLayer(ln,f,l)  stores a pair of iterators in f and l
    //                          such that the loop
    //
    //                          for (ConstIterator i = f; f != l; ++i)
    //                             ...
    //
    //                          iterates over all channels in layer ln.
    //                          channelsInLayer (ln, l, p) calls
    //                          channelsWithPrefix (ln + ".", l, p).
    //
    //-----------------------------------------------------------------

    void                layers (std::set <std::string> &layerNames) const;

    void                channelsInLayer (const std::string &layerName,
                                         Iterator &first,
                                         Iterator &last);

    void                channelsInLayer (const std::string &layerName,
                                         ConstIterator &first,
                                         ConstIterator &last) const;


    //-------------------------------------------------------------------
    // Find all channels whose name begins with a given prefix:
    //
    // channelsWithPrefix(p,f,l) stores a pair of iterators in f and l
    // such that the following loop iterates over all channels whose name
    // begins with string p:
    //
    //          for (ConstIterator i = f; f != l; ++i)
    //              ...
    //
    //-------------------------------------------------------------------

    void                        channelsWithPrefix (const char prefix[],
                                                    Iterator &first,
                                                    Iterator &last);

    void                        channelsWithPrefix (const char prefix[],
                                                    ConstIterator &first,
                                                    ConstIterator &last) const;

    ...
};