Appendix B. Supporting Additional File Formats

Table of Contents

The Shared Object
The .desktop File
Compiling and Copying

Warning

WARNING: This section was written for Kst version 1 and may be somewhat, or even totally obsolete. WARNING

This section describes how to create additional readers for unsupported file formats. If you are not already familiar with data source concepts, please read Data Source Concepts

Creating Datasource Readers

If you wish to use a file format other than those currently supported, you might choose to write custom datasource readers.

All Kst datasource readers are regular KDE plugins. Like all KDE plugins, each datasource reader must have a shared object file and a *.desktop file. Before writing the reader, the library name of the plugin must be decided. This name must be a valid variable name in C, as it will be used in the function names of the shared object. For example, the library name of the reader for ASCII files is “ascii”.

Note

KDE plugins are not the same as the Kst plugins used to manipulate data. All references to plugins in this section are to KDE plugins.

The Shared Object

A datasource reader should be a subclass of the abstract KstDataSource class. Ensure that you include the header file for KstDataSource in the source code for your datasource reader:

#include <kstdatasource.h>

There are certain requirements that a datasource reader must meet. One requirement concerns the presence of exported C functions. Other requirements are consequences of the fact that datasource readers inherit from KstDataSource. Both sets of requirements, along with suggestions and general explanations, are provided in the following sections.

Exported C Functions

The exported C functions are listed below. In the following examples, all instances of <libname> should be replaced with the actual library name of the plugin.

KstDataSource *create_<libname>(const QString& filename, const QString& type): This function should create a new datasource reader of type <libname>, where <libname> is the library name of the plugin. A pointer of type KstDataSource to the new reader should be returned.
bool understands_<libname>(const QString& filename): This function should return true if the file specified by filename is of a valid type supported by this reader, and false otherwise. The function should check the contents of the file for validity, and not rely on any filename extensions.
QStringList provides_<libname>(): This function should return a QStringList of the file types supported by this reader. The strings returned are arbitrary, but should be descriptive of and appropriate for the actual file types.

Protected Member Variables

KstDataSource contains various protected member variables that the custom datasource reader can use. These variables are described below.

bool _valid: This variable should be true if the custom datasource reader is valid. Most likely the reader will be valid, unless there is an error condition (such as the data file being unreadable by the reader). This variable is used by the isValid() function of KstDataSource, which is usually not reimplemented in subclasses.
QStringList _fieldList: This variable should hold a list of the field names in the data source.
QString _filename: This variable should hold the name of the data file this datasource reader is associated with.
QString _source: This variable should hold the type name of the source.

Virtual Functions

The KstDataSource class contains many virtual functions that should be redefined in the custom datasource reader. These functions are in the template files template.h and template.cpp, listed in the Example Templates section. Descriptions of the functions follow.

TemplateSource(const QString& filename, const QString& type): The constructor for the datasource reader. filename is the name of the file to read data from, and type is the type of data the file contains. This constructor should most likely invoke the KstDataSource constructor in the constructor initializer list, and probably call the update function listed below to initialize member variables. In particular, the bool _valid variable should be set appropriately.
virtual ~TemplateSource(): The destructor for the datasource reader. Any dynamically allocated memory should be freed.
virtual KstObject::UpdateType update(int = -1): This function should read any new data entered in the data file since the last time update was called, and update the member variables appropriately. The function should return KstObject::UPDATE if the file contained changes, or KstObject::NO_CHANGE otherwise.
virtual int readField(double *v, const QString &field, int s, int n): This function should read n frames of data, starting at frame s from the field specified by the field name field, and return the contents in the array v. If n is less than 0, the function should instead read 1 sample from the start of frame s. The number of samples that were read should be returned.
virtual bool isValidField(const QString &field) const: This function should return true of the field specified by the field name field is a valid field in the current data source, or false if the field is not a valid field.
virtual int samplesPerFrame(const QString& field): This function should return the ratio of samples per frame for the field specified by the field name field. For data sources that do not make use of this concept, the number of samples per frame can be set to 1.
virtual int frameCount() const: This function should return the total number of frames in the data source, as of the last time update was called.
virtual QString fileType() const: This function should return the file type of the data file currently being used, usually the same as the type parameter that was passed to the constructor. Alternatively, it can contain an error message (to indicate, for example, that the file is not valid).
virtual void save(QTextStream &ts): This function should save the file description information to ts. In most cases the implementation provided by KstDataSource should be sufficient.

Example Templates

In general, the following two template files can be used to create new shared object files. Simply modify the function bodies as appropriate for your particular data source.

/***************************************************************************
                  template.h  -  data source plugin template
                             -------------------
    begin                : Fri Oct 17 2003
    copyright            : (C) 2003 The University of Toronto
    email                :
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#ifndef TEMPLATE_H
#define TEMPLATE_H

#include &lt;kstdatasource.h&gt;


class TemplateSource : public KstDataSource {
public:
  TemplateSource(const QString& filename, const QString& type);

  virtual ~TemplateSource();

  virtual KstObject::UpdateType update(int = -1);

  virtual int readField(double *v, const QString &field, int s, int n);

  virtual bool isValidField(const QString &field) const;

  virtual int samplesPerFrame(const QString &field);

  virtual int frameCount() const;

  virtual QString fileType() const;

  virtual void save(QTextStream &ts);
};


#endif

/***************************************************************************
                    template.cpp  -  data source template
                             -------------------
    begin                : Fri Oct 17 2003
    copyright            : (C) 2003 The University of Toronto
    email                :
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#include "template.h"


TemplateSource::TemplateSource(const QString& filename, const QString& type)
: KstDataSource(filename, type) {
}


TemplateSource::~TemplateSource() {
}


KstObject::UpdateType TemplateSource::update(int u) {
  Q_UNUSED(u)
  return KstObject::NO_CHANGE;
}


int TemplateSource::readField(double *v, const QString& field, int s, int n) {
  Q_UNUSED(v)
  Q_UNUSED(field)
  Q_UNUSED(s)
  Q_UNUSED(n)
  return -1;
}


bool TemplateSource::isValidField(const QString& field) const {
  Q_UNUSED(field)
  return false;
}


int TemplateSource::samplesPerFrame(const QString &field) {
  Q_UNUSED(field)
  return 0;
}


int TemplateSource::frameCount() const {
  return 0;
}


QString TemplateSource::fileType() const {
  return QString::null;
}


void TemplateSource::save(QTextStream &ts) {
  KstDataSource::save(ts);
}


extern "C" {
KstDataSource *create_template(const QString& filename, const QString& type) {
  return new TemplateSource(filename, type);
}

QStringList provides_template() {
  QStringList rc;
  // create the stringlist
  return rc;
}

bool understands_template(const QString& filename) {
  // determine if it is an X file
  Q_UNUSED(filename)
  return false;
}

}

The `.desktop` File

The following is an example of a .desktop file for the template plugin:

[Desktop Entry]
Encoding=UTF-8
Type=Service
ServiceTypes=Kst Data Source
X-KDE-ModuleType=Plugin
X-Kst-Plugin-Library=template
X-Kst-Plugin-Author=The University of Toronto
Name=File Reader Template
Comment=Long description of the file reader template.

You should add translations in additional languages for the Name and Comment fields by adding additional Name and Comment fields with [xx] appended to the end of the field names, where xx is the two-letter language code. For example, to add Spanish translations, the following lines would need to be added:

Name[es]=Plantilla de lectura de ficheros
Comment[es]=Plantilla de código para hacer un complemento de lectura de ficheros.

The field X-Kst-Plugin-Library should be exactly the same as the decided library name for the plugin.

Compiling and Copying

To compile and install the new custom datasource reader, create a new directory under kst/datasources of the source package. Place the source files for the object, along with the .desktop file in the new directory. Then, edit kst/datasources/Makefile.am so that SUBDIRS contains the name of the new subdirectory. For example, if the new subdirectory is called template, SUBDIRS might be changed to the following:

SUBDIRS=ascii dirfile frame indirect template $(PIOLIB_SUBDIR) $(FITSIO_SUBDIR)

After the required files are in the newly created subdirectory, a Makefile.am needs to be created in there as well. Use the following sample as a template, replacing all instances of “template” with your custom library name in kde_module_LTLIBRARIES, kstdata_template_la_SOURCES and services_DATA.

INCLUDES=-I$(srcdir)/../.. $(all_includes)

kde_module_LTLIBRARIES=kstdata_template.la

kstdata_template_la_LDFLAGS=$(all_libraries) -module -avoid-version
kstdata_template_la_SOURCES=template.cpp

METASOURCES=AUTO

services_DATA=kstdata_template.desktop
servicesdir=$(kde_servicesdir)/kst

Once this is done, you can compile and re-install Kst from the modified source package, or alternatively, only install the new libraries, like follows (using the “template” subdirectory as an example). First change to the root directory of the Kst source package. Then,

./configure --prefix=`kde-config --prefix`
cd ./kst/datasources/template
make
make install

Restart Kst and the new datasource reader should be loaded.

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Supporting Additional File Formats