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docs/Customizing/Custom-output-interface.md

@@ -0,0 +1,240 @@
+# Custom `QROutputInterface`
+
+Let's suppose that you want to create your own output interface because there's no built-in output class that supports the format you need for your application.
+In this example we'll create a string output class that outputs the coordinates for each module, separated by module type.
+
+
+## Class skeleton
+
+We'll start with a skeleton that extends  `QROutputAbstract` and implements the methods that are required by `QROutputInterface`:
+
+```php
+class MyCustomOutput extends QROutputAbstract{
+
+	public static function moduleValueIsValid($value):bool{}
+
+	protected function prepareModuleValue($value){}
+
+	protected function getDefaultModuleValue(bool $isDark){}
+
+	public function dump(string $file = null){}
+
+}
+```
+
+
+## Module values
+
+The validator should check whether the given input value and range is valid for the output class and if it can be given to the `QROutputAbstract::prepareModuleValue()` method.
+For example in the built-in GD output it would check if the value is an array that has a minimum of 3 elements (for RGB), each of which is numeric.
+
+In this example we'll accept string values, the characters `a-z` (case-insensitive) and a hyphen `-`:
+
+```php
+	public static function moduleValueIsValid($value):bool{
+		return is_string($value) && preg_match('/^[a-z-]+$/i', $value) === 1;
+	}
+```
+
+To prepare the final module substitute, you should transform the given (validated) input value in a way so that it can be accessed without any further calls or transformation.
+In the built-in output for example this means it would return an `ImagickPixel` instance or the integer value returned by `imagecolorallocate()` on the current `GdImage` instance.
+
+For our example, we'll lowercase the validated string:
+
+```php
+	protected function prepareModuleValue($value):string{
+		return strtolower($value);
+	}
+```
+
+Finally, we need to provide a default value for dark and light, you can call `prepareModuleValue()` here if necessary.
+We'll return an empty string `''` here as we're going to use the `QROutputInterface::LAYERNAMES` constant for non-existing values
+(returning `null` would run into an exception in `QROutputAbstract::getModuleValue()`).
+
+```php
+	protected function getDefaultModuleValue(bool $isDark):string{
+		return '';
+	}
+```
+
+
+## Transform the output
+
+In our example, we want to collect the modules by type and have the collections listed under a header for each type.
+In order to do so, we need to collect the modules per `$M_TYPE` before we can render the final output.
+
+```php
+	public function dump(string $file = null):string{
+		$collections = [];
+
+		// loop over the matrix and collect the modules per layer
+		foreach($this->matrix->getMatrix() as $y => $row){
+			foreach($row as $x => $M_TYPE){
+				$collections[$M_TYPE][] = $this->module($x, $y, $M_TYPE);
+			}
+		}
+
+		// build the final output
+		$out = [];
+
+		foreach($collections as $M_TYPE => $collection){
+			$name  = ($this->getModuleValue($M_TYPE) ?: $this::LAYERNAMES[$M_TYPE]);
+			// the section header
+			$out[] = sprintf("%s (%012b)\n", $name, $M_TYPE);
+			// the list of modules
+			$out[] = sprintf("%s\n", implode("\n", $collection));
+		}
+
+		return implode("\n", $out);
+	}
+```
+
+We've introduced another method that handles the module rendering, which incooperates handling of the `QROptions::$drawLightModules` setting:
+
+```php
+	protected function module(int $x, int $y, int $M_TYPE):string{
+
+		if(!$this->drawLightModules && !$this->matrix->isDark($M_TYPE)){
+			return '';
+		}
+
+		return sprintf('x: %s, y: %s', $x, $y);
+	}
+```
+
+Speaking of option settings, there's also `QROptions::$connectPaths` which we haven't taken care of yet - the good news is that we don't need to as it is already implemented!
+We'll modify the above `dump()` method to use `QROutputAbstract::collectModules()` instead.
+
+The module collector accepts a closure as its only parameter, the closure is called with 4 parameters:
+
+- `$x`           : current column
+- `$y`           : current row
+- `$M_TYPE`      : field value
+- `$M_TYPE_LAYER`: (possibly modified) field value that acts as layer id
+
+We'll only need the first 3 parameters, so our closure would look as follows:
+
+```php
+$closure = fn(int $x, int $y, int $M_TYPE):string => $this->module($x, $y, $M_TYPE);
+```
+
+As of PHP 8.1+ we can narrow this down with the [first class callable syntax](https://www.php.net/manual/en/functions.first_class_callable_syntax.php):
+
+```php
+$closure = $this->module(...);
+```
+
+This is our final output method then:
+
+```php
+	public function dump(string $file = null):string{
+		$collections = $this->collectModules($this->module(...));
+
+		// build the final output
+		$out = [];
+
+		foreach($collections as $M_TYPE => $collection){
+			$name  = ($this->getModuleValue($M_TYPE) ?: $this::LAYERNAMES[$M_TYPE]);
+			// the section header
+			$out[] = sprintf("%s (%012b)\n", $name, $M_TYPE);
+			// the list of modules
+			$out[] = sprintf("%s\n", implode("\n", $collection));
+		}
+
+		return implode("\n", $out);
+	}
+```
+
+
+## Run the custom output
+
+To run the output we just need to set the `QROptions::$outputInterface` to our custom class:
+
+```php
+$options = new QROptions;
+$options->outputType       = QROutputInterface::CUSTOM;
+$options->outputInterface  = MyCustomOutput::class;
+$options->connectPaths     = true;
+$options->drawLightModules = true;
+
+// our custom module values
+$options->moduleValues    = [
+	QRMatrix::M_DATA      => 'these-modules-are-light',
+	QRMatrix::M_DATA_DARK => 'here-is-a-dark-module',
+];
+
+$qrcode = new QRCode($options);
+$qrcode->addByteSegment('test');
+
+var_dump($qrcode->render());
+```
+
+The output looks similar to the following:
+```
+these-modules-are-light (000000000010)
+
+x: 0, y: 0
+x: 1, y: 0
+x: 2, y: 0
+...
+
+here-is-a-dark-module (100000000010)
+
+x: 4, y: 4
+x: 5, y: 4
+x: 6, y: 4
+...
+```
+
+Profit!
+
+
+## Summary
+
+We've learned how to create a custom output class for a string based format similar to several of the built-in formats such as SVG or EPS.
+
+The full code of our custom class below:
+
+```php
+class MyCustomOutput extends QROutputAbstract{
+
+	protected function prepareModuleValue($value):string{
+		return strtolower($value);
+	}
+
+	protected function getDefaultModuleValue(bool $isDark):string{
+		return '';
+	}
+
+	public static function moduleValueIsValid($value):bool{
+		return is_string($value) && preg_match('/^[a-z-]+$/i', $value) === 1;
+	}
+
+	public function dump(string $file = null):string{
+		$collections = $this->collectModules($this->module(...));
+
+		// build the final output
+		$out = [];
+
+		foreach($collections as $M_TYPE => $collection){
+			$name  = ($this->getModuleValue($M_TYPE) ?: $this::LAYERNAMES[$M_TYPE]);
+			// the section header
+			$out[] = sprintf("%s (%012b)\n", $name, $M_TYPE);
+			// the list of modules
+			$out[] = sprintf("%s\n", implode("\n", $collection));
+		}
+
+		return implode("\n", $out);
+	}
+
+	protected function module(int $x, int $y, int $M_TYPE):string{
+
+		if(!$this->drawLightModules && !$this->matrix->isDark($M_TYPE)){
+			return '';
+		}
+
+		return sprintf('x: %s, y: %s', $x, $y);
+	}
+
+}
+```

docs/Readme.md

@@ -68,6 +68,7 @@ The markdown sources for the [Read the Docs online manual](https://php-qrcode.re
 
 - [Module values](./Customizing/Module-Values.md)
 - [`QROutputAbstract`](./Customizing/QROutputAbstract.md)
+- [Custom `QROutputInterface`](./Customizing/Custom-output-interface.md)
 
 
 ### Built-In Output Modules

docs/Usage/Overview.md

@@ -60,6 +60,7 @@ For the QR Code reader, either `ext-gd` or `ext-imagick` is required!
   - [twill](https://github.com/area17/twill)
   - [Elefant CMS](https://github.com/jbroadway/elefant)
   - [OSIRIS](https://github.com/JKoblitz/osiris)
+  - [EspoCRM](https://github.com/espocrm/espocrm)
 - Articles:
   - [Twilio: How to Create a QR Code in PHP](https://www.twilio.com/blog/create-qr-code-in-php) (featuring v4.3.x)
 

docs/index.rst

@@ -28,6 +28,7 @@ This work is licensed under the Creative Commons Attribution 4.0 International (
 
    Customizing/Module-Values.md
    Customizing/QROutputAbstract.md
+   Customizing/Custom-output-interface.md
 
 .. toctree::
    :maxdepth: 3