Assuming that the library is installed where it can be found by PHP it is now very simple to create a basic Data Matrix symbol using just default values. We first show the complete first example and then discuss it. In the following scripts we will assume that the include path has the core JpGraph directory in its path.

All barcode creation follows the following basic three steps :

The following script shows how to create the simplest possible barcode (in PNG format) representing the data string "The first datamatrix" encoded using all default values. The resulting barcode is shown in Figure 26.5

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<?php // content="text/plain; charset=utf-8"
require_once('jpgraph/datamatrix/datamatrix.inc.php');
 
$data = 'The first datamatrix';
 
$encoder = DatamatrixFactory::Create();
$backend = DatamatrixBackendFactory::Create($encoder);
$backend->Stroke($data);
?>

Figure 26.5. The simplest possible datamatrix script (datamatrix_ex00.php)

(As can be seen this follows the same principles as the creation of PDF417 symbols)

The principle is the same for all type of data matrix symbol creations. We first create an instance of the chosen encoder. In this case a standard ECC-200 encoder by creating an instance of class Datamatrix. We then create a suitable backend that handles the output of the barcode. By default the output will be an image encoded in the PNG image format.

The final step is to send back the generated image to the browser with a call to the method Backend::Stroke() with the data to be encoded as its first argument.

The example above does not have any error handling. If there is some error in the process an exception will be thrown in the same way as in other places in the library. The default exception will display a standard library image error box. An example of this is shown in Figure 26.6.

Figure 26.6. Datamatrix error image

If some additional processing is necessary and just display a text based re-formatted error message we could change the above code to catch this exception as the following example shows.

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<?php // content="text/plain; charset=utf-8"
require_once('jpgraph/datamatrix/datamatrix.inc.php');
 
$data = 'The first datamatrix';
$encoder = DatamatrixFactory::Create();
$encoder->SetEncoding(ENCODING_ASCII);
$backend = DatamatrixBackendFactory::Create($encoder);
 
// We increase the module width to 3 pixels
$backend->SetModuleWidth(3);
 
try {
    $backend->Stroke($data);
} catch (Exception $e) {
    echo 'Datamatrix error: '.$e->GetMessage()."\n";
    exit(1);
}
?>

Figure 26.7. Datamatrix with basic error handling (datamatrix_ex0.php)

In contrast to the PDF417 encodation process there is no option to select an level of error correction. The error correction level is automatically specified in the standard depending on the size of the barcode. As a final initial example the next script uses the backend method Backend::SetModuleWidth($aWidth) to increase the width of one module.

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<?php // content="text/plain; charset=utf-8"
require_once('jpgraph/datamatrix/datamatrix.inc.php');
 
$data = '123456';
 
$encoder = DatamatrixFactory::Create();
$backend = DatamatrixBackendFactory::Create($encoder);
$backend->SetModuleWidth(3);
 
// Create the barcode from the given data string and write to output file
try {
    $backend->Stroke($data);
} catch (Exception $e) {
    $errstr = $e->GetMessage();
    echo "Datamatrix error message: $errstr\n";
}
 
?>

Figure 26.8. Datamatrix with modified module width (datamatrix_ex1.php)

As in other parts of the library the Datamatrix module throws an exception when an error occurs. As shown in the previous section an error image is the default if no explicit try {} catch {} statement is added to the script.

The script below shows how to catch the error, do some possible clean up and then explicitly create and send back the error image.

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<?php
...
try {
    $backend->Stroke($data);
} catch( Exception $e ) {
    doCleanup();
    $errobj = new DMErrObjectImg();
    $errobj->Raise($e->getMessage());    
}
?>

another variant of this would be to re-throw the exception after the cleanup has been performed as the following example shows

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<?php
...
try {
    $backend->Stroke($data);
} catch( Exception $e ) {
    doCleanup();
    throw $e;
}
?>

It is also possible to get hold of the internal error code that corresponds to each error message by calling the PHP standard exception method Exception::getCode() as the following example shows

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<?php
...
try {
    $backend->Stroke($data);
} catch (Exception $e) {
    $errstr = $e->GetMessage();
    $errcode = $e->GetCode();
    echo "Datamatrix error ($errcode). Message: $errstr\n";
}
?>

Table 26.3 lists the errors that can be thrown by the datamatrix module (the table deliberately excludes internal error messages).

The primary encodation option is to manually specify the shape of the Datamatrix barcode. By default the symbol size will be chosen as the smallest possible. However some application require that usage of a fixed size symbol shape.

The available shapes are listed in Table 26.2. The wanted shape is specified when the instance of the encoder is created or by a call to Datamatrix::SetSize(). The shape is specified by a symbolic constant that corresponds to each available shape in Table 26.2. The symbol name is "DMAT_<H>x<W>" where <H> is the height (in modules) and <W> is the width (in modules). For example the following line specifies a 24 module square symbol

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$encoder->SetSize(DMAT_24x24);

In addition to the sizes specified in Table 26.2 there is also an option to specify automatic sizing (which is the default). The following script sets the sizing to be automatic.

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$encoder->SetSize(DMAT_AUTO);

As was discussed in Section 26.1.5 there are several ways by which data can be encoded. By default the encoder will use an optimal algorithm to create a combination of the available encodation schema to create the smallest possible symbol. In some application it might however be stated that a specific encodation method should be chosen.

The encoding method is a property of the encodation class and is set with a call to

The encoding is specified as one of the symbolic constants shown in Table 26.4

The following example sets the ASCII encodation schema

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$encoder->SetEncoding(ENCODING_ASCII);

The default automatic encoding is the same as

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$encoder->SetSize(ENCODING_AUTO);

In order to allow the specification of special input data in normal ASCII encodation for easy entering from a keyboard the library supports what is commonly known as "tilde" processing. When this is enabled (it is disabled by default) certain character sequences that begins with a tilde sign (i.e. "~") will be translated to a special ASCII value that cannot normally be entered from a keyboard.

When tilde mode is enabled with a call to the method

Table 26.5 lists the translations that will then be enabled on the input data. Some of the translations are technical and requires full understanding of Datamatrix standard to be used.

In order to create the actual output one or more backends must be created. The Datamatrix supports the following backends:

The following code snippet shows two ways of creating a barcode image backend.

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// Create an image backend
$backend = DatamatrixBackendFactory::Create($encoder);

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// Create an image backend
$backend = DatamatrixBackendFactory::Create($encoder, BACKEND_IMAGE);

The following code shows a complete script to generate a postscript output

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<?php
require_once('jpgraph/datamatrix/datamatrix.inc.php');
$data = '0123456789';
 
// Create and set parameters for the encoder
$encoder = DatamatrixFactory::Create();
 
// Create the image backend (default)
$backend = DatamatrixBackendFactory::Create($encoder, BACKEND_PS);
try {
    $ps_txt = $backend->Stroke($data);
    echo '<pre>'.$ps_txt.'</pre>';
} catch (Exception $e) {
    $errstr = $e->GetMessage();
    echo "Datamatrix error message: $errstr\n";
}
?>

The following methods are available to adjust the final look and feel of the barcode

For the image backend it is possible to adjust the image encoding format with the following method

For postscript backend it is possible to select whether the postscript should be generated as encapsulated postscript. This is controlled by the method

In the example directory in the distribution ('datamatrix/examples') you can find many more examples on how to create barcodes. As a good start the following (simple) template may be used as a base for further customizations.

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<?php
require_once('jpgraph/datamatrix/datamatrix.inc.php');
 
$data = '0123456789';
 
$shape       = DMAT_AUTO;
$encoding    = ENCODING_AUTO;
$modulewidth = 3;
$quietzone   = 10;
$color1      = 'black';
$color0      = 'white';
$colorq      = 'white';
$outputfile  = '';
 
// Create and set parameters for the encoder
$encoder = DatamatrixFactory::Create($shape);
$encoder->SetEncoding($encoding);
 
// Create the image backend (default)
$backend = DatamatrixBackendFactory::Create($encoder);
 
// By default the module width is 2 pixel so we increase it a bit
$backend->SetModuleWidth($modulewidth);
 
// Set Quiet zone
$backend->SetQuietZone($quietzone);
 
// Set other than default colors (one, zero, quiet zone/background)
$backend->SetColor($color1, $color0, $colorq);
 
// Create the barcode from the given data string and write to output file
try {
    $backend->Stroke($data,$outputfile);
} catch (Exception $e) {
    $errstr = $e->GetMessage();
    echo "Datamatrix error message: $errstr\n";
}
?>

As an example the library includes a WEB-based demo barcode creation application. This application can be used to easily create barcode through it's WEB interface. It is available at 'datamatrix/demoapp/index.html'

This application is primarily included as a demo on the features available in the library and not as a finalized product.

Figure 26.9 shows a screen shot of the application interface.

Figure 26.9. Datamatrix WEB-based demo application