All barcode implementations are derived from the abstract glbarcode::Barcode class. The glbarcode::Barcode1dBase subclass of glbarcode::Barcode provides a common framework for the implementation of 1D barcodes. Therefore, creating new 1D barcode types (or symbologies) would be typically accomplished by implementing a subclass of this glbarcode::Barcode1dBase class rather than directly implementing the glbarcode::Barcode class.

Virtual Methods

A 1D barcode subclass must implement the following virtual methods (or callbacks):

glbarcode::Barcode1dBase::validate() – The validate method is used to test if data is valid for encoding with the intended symbology. This method must only validate data that can be encoded successfully as-is or after processing by the optional glbarcode::Barcode1dBase::preprocess() method.
glbarcode::Barcode1dBase::encode() – The encode method is used to encode data such that it can later be vectorized. The encoded data is usually a list of characters that represent an atomic barcode element. For example, the following is the character encoding used by the Code39 implementation:

Character Meaning

N A narrow bar.

W A wide bar.

n A narrow space (gap between bars)

w A wide space (gap between bars)

i Inter-symbol gap

Other encoding examples can be found in the existing barcode implementations.
glbarcode::Barcode1dBase::vectorize() – The vectorize method converts the encoded data into a list of Drawing Primitives suitable for rendering. The following protected methods are available to the vectorize implementation to create this list:

A barcode subclass may also need to implement the following virtual methods:

glbarcode::Barcode1dBase::preprocess() – The preprocess method performs any transformation of the data needed before encoding. This method may be needed to perform a first-pass encoding to translate an extended alphabet into a simpler one. For example, this could be as simple as upshifting lowercase letters into uppercase if the symbology only supports uppercase. It is assumed that the data passed to this method has already been validated with the glbarcode::Barcode1dBase::validate() method.
glbarcode::Barcode1dBase::prepareText() – The prepareText method performs any transformation of the data needed before it can be displayed.

The following figure illustrates the data flow between these methods, which are called by glbarcode::Barcode1dBase::build():

Registering With The Barcode Factory

To be able to register a barcode type with the barcode factory, it must implement a static create method that returns a pointer to a newly allocated barcode:

using namespace glbarcode;
 
Barcode* BarcodeXxx::create( void )
{
        return new BarcodeXxx();
}

This is used to register the barcode using glbarcode::Factory::registerType:

using namespace glbarcode;
 
Factory::registerType( "xxx", &BarcodeXxx::create )

Full Example

As a complete example, the following is the glbarcode++ implementation of a custom barcode type called "mybarcode".

MyBarcode.hpp:

/*  MyBarcode.hpp */
    
#ifndef _MyBarcode_hpp_
#define _MyBarcode_hpp_
        
        
#include "glbarcode/Barcode1dBase.hpp"
         
         
class MyBarcode : public glbarcode::Barcode1dBase
{
public:
        static glbarcode::Barcode* create( void );
        
        
private:
        bool validate( const std::string& rawData );
        
        std::string encode( const std::string& cookedData );
        
        std::string prepareText( const std::string& rawData );
        
        void vectorize( const std::string& codedData,
                        const std::string& displayText,
                        const std::string& cookedData,
                        double&            w,
                        double&            h );
};
        
        
#endif /* _MyBarcode_h_ */

MyBarcode.cpp:

/*  MyBarcode.cpp */
    
#include "MyBarcode.hpp"
         
#include "glbarcode/Constants.hpp"
         
#include <cctype>
#include <algorithm>
         
         
using namespace glbarcode::Constants;
      
      
/*-----------------------------------*/
/* Private data.                     */
/*-----------------------------------*/
namespace
{
        /* My barcode alphabet. Position indicates value. */
        const std::string alphabet = "0123456789ABCDEF";
        
        /* My barcode symbols. Position must match position in alphabet. */
        const std::string symbols[] = {
                /*        BsBsBsBsB */
                /* 0 */  "NnNwWnWnN",
                /* 1 */  "WnNwNnNnW",
                /* 2 */  "NnWwNnNnW",
                /* 3 */  "WnWwNnNnN",
                /* 4 */  "NnNwWnNnW",
                /* 5 */  "WnNwWnNnN",
                /* 6 */  "NnWwWnNnN",
                /* 7 */  "NnNwNnWnW",
                /* 8 */  "WnNwNnWnN",
                /* 9 */  "NnWwNnWnN",
                /* A */  "WnNnNwNnW",
                /* B */  "NnWnNwNnW",
                /* C */  "WnWnNwNnN",
                /* D */  "NnNnWwNnW",
                /* E */  "WnNnWwNnN",
                /* F */  "NnWnWwNnN",
        };
        
        const std::string frameSymbol = "NwNnWnWnN";
        
        /* Vectorization constants */
        const double MIN_X       = ( 0.01 *  PTS_PER_INCH );
        const double N           = 2.5;
        const double MIN_I       = MIN_X;
        const double MIN_HEIGHT  = ( 0.25 *  PTS_PER_INCH );
        const double MIN_QUIET   = ( 0.10 *  PTS_PER_INCH );
        
        const double MIN_TEXT_AREA_HEIGHT = 14.0;
        const double MIN_TEXT_SIZE        = 10.0;
}
        
        
/*----------------------------------------------------------------------*/
/* Static barcode creation method                                       */
/*----------------------------------------------------------------------*/
glbarcode::Barcode* MyBarcode::create( void )
{
        return new MyBarcode();
}
        
        
/*----------------------------------------------------------------------*/
/* My barcode data validation, implements Barcode1dBase::validate()     */
/*----------------------------------------------------------------------*/
bool MyBarcode::validate( const std::string& rawData )
{
        for ( int i = 0; i < rawData.size(); i++ )
        {
                char c = toupper( rawData[i] );
                
                if ( alphabet.find(c) == std::string::npos )
                {
                        return false;
                }
        }
        
        return true;
}
        
        
/*----------------------------------------------------------------------*/
/* My barcode data encoding, implements Barcode1dBase::encode()         */
/*----------------------------------------------------------------------*/
std::string MyBarcode::encode( const std::string& cookedData )
{
        std::string code;
        
        /* Left frame symbol */
        code += frameSymbol;
        code += "i";
        
        int sum = 0;
        for ( int i=0; i < cookedData.size(); i++ )
        {
                int cValue = alphabet.find( toupper( cookedData[i] ) );
                
                code += symbols[cValue];
                code += "i";
                
                sum += cValue;
        }
        
        if ( checksum() )
        {
                code += symbols[sum % 16];
                code += "i";
        }
        
        /* Right frame symbol */
        code += frameSymbol;
        
        return code;
}
        
        
/*----------------------------------------------------------------------*/
/* Prepare text for display, implements Barcode1dBase::prepareText()    */
/*----------------------------------------------------------------------*/
std::string MyBarcode::prepareText( const std::string& rawData )
{
        std::string displayText;
        
        for ( int i = 0; i < rawData.size(); i++ )
        {
                displayText += toupper( rawData[i] );
        }
        
        return displayText;
}
        
        
/*----------------------------------------------------------------------*/
/* My barcode vectorization, implements Barcode1dBase::vectorize()      */
/*----------------------------------------------------------------------*/
void MyBarcode::vectorize( const std::string& codedData,
                           const std::string& displayText,
                           const std::string& cookedData,
                           double&            w,
                           double&            h )
{
        /* determine width and establish horizontal scale, based on original cooked data */
        double dataSize = cookedData.size();
        double minL;
        if ( !checksum() )
        {
                minL = (dataSize + 2)*(3*N + 6)*MIN_X + (dataSize + 1)*MIN_I;
        }
        else
        {
                minL = (dataSize + 3)*(3*N + 6)*MIN_X + (dataSize + 2)*MIN_I;
        }
                
        double scale;
        if ( w == 0 )
        {
                scale = 1.0;
        }
        else
        {
                scale = w / (minL + 2*MIN_QUIET);
 
                if ( scale < 1.0 )
                {
                        scale = 1.0;
                }
        }
        double width = minL * scale;
        
        /* determine text parameters */
        double hTextArea = scale * MIN_TEXT_AREA_HEIGHT;
        double textSize   = scale * MIN_TEXT_SIZE;
        
        /* determine height of barcode */
        double height = showText() ? h - hTextArea : h;
        height = std::max( height, std::max( 0.15*width, MIN_HEIGHT ) );
        
        /* determine horizontal quiet zone */
        double xQuiet = std::max( (10 * scale * MIN_X), MIN_QUIET );
        
        /* Now traverse the code string and draw each bar */
        double x1 = xQuiet;
        for ( int i=0; i < codedData.size(); i++ )
        {
                double lwidth;
                                                
                switch ( codedData[i] )
                {
                
                case 'i':
                        /* Inter-character gap */
                        x1 += scale * MIN_I;
                        break;
                        
                case 'N':
                        /* Narrow bar */
                        lwidth = scale*MIN_X;
                        addLine( x1, 0.0, lwidth, height );
                        x1 += scale * MIN_X;
                        break;
                        
                case 'W':
                        /* Wide bar */
                        lwidth = scale*N*MIN_X;
                        addLine( x1, 0.0, lwidth, height );
                        x1 += scale * N * MIN_X;
                        break;
                        
                case 'n':
                        /* Narrow space */
                        x1 += scale * MIN_X;
                        break;
                        
                case 'w':
                        /* Wide space */
                        x1 += scale * N * MIN_X;
                        break;
                        
                default:
                        // NOT REACHED
                        break;
                }
        }
        
        if ( showText() )
        {
                std::string starredText = "*" + displayText + "*";
                addText( xQuiet + width/2, height + (hTextArea+0.7*textSize)/2, textSize, starredText );
        }
        
        /* Overwrite requested size with actual size. */
        w = width + 2*xQuiet;
        h = showText() ? height + hTextArea : height;
}

Now to put it into action.

main.c:

/* main.cpp */
   
#include "MyBarcode.h"
         
#include <glbarcode/Factory.h>
#include <glbarcode/RendererSvg.h>
         
using namespace glbarcode;
      
int main( int argc, char **argv )
{
        /* Register my barcode with factory. */
        Factory::registerType( "mybarcode", MyBarcode::create );
        
        /* Create barcode object. */
        Barcode *bc = Factory::createBarcode( "mybarcode" );
        
        /* Set barcode options to show text and generate check digit, and then build */
        bc->setChecksum(true).setShowText(true).build( "c0de0016", 288, 72 );
        
        /* Render barcode. */
        bc->render( RendererSvg().setFilename( "MyBarcodeExample.svg" ) );
        
        /* Cleanup. */
        delete bc;
}

This example will produce the following SVG file:

Output of above example 'MyBarcodeExample.svg'

Character	Meaning
N	A narrow bar.
W	A wide bar.
n	A narrow space (gap between bars)
w	A wide space (gap between bars)
i	Inter-symbol gap