Watermark behind text

To fix this, you can adjust the `watermarkImgBehind` setting so that the watermark appears behind the text instead. Based on your provided function, here's how to do it:

### Solution:
Ensure that the watermark is set to be rendered behind the text by setting `$this->watermarkImgBehind` to `true`.

**Here's the adjusted function:**

function watermarkImg($src, $alpha = 0.2)
{
    if ($this->PDFA || $this->PDFX) {
        throw new MpdfMpdfException('PDFA and PDFX do not permit transparency, so mPDF does not allow Watermarks!');
    }

    // Ensure the watermark is behind the text
    $this->watermarkImgBehind = true; // Add this line if it's not already set

    if ($this->watermarkImgBehind) {
        $this->watermarkImgAlpha = $this->SetAlpha($alpha, 'Normal', true);
    } else {
        $this->SetAlpha($alpha, $this->watermarkImgAlphaBlend);
    }

    // Render the watermark image
    $this->Image($src, 0, 0, 0, 0, '', '', true, true, true);

    // Reset the transparency for subsequent text rendering
    if (!$this->watermarkImgBehind) {
        $this->SetAlpha(1);
    }
}

### Explanation:
1. **Ensure the watermark is behind text**: The key line here is:

$this->watermarkImgBehind = true;

This makes sure the watermark image is rendered behind all the content.

2. **Reset Alpha Transparency**: The line:

$this->SetAlpha(1);

ensures that any subsequent content is rendered with full opacity.

### Additional Tips:
– If `$this->watermarkImgBehind` is already set elsewhere in your code or configuration, make sure it's set before calling the `watermarkImg()` function.
– Ensure that your text rendering code comes **after** calling the `watermarkImg()` function, so that the text is layered above the watermark.

This adjustment should resolve the issue with your watermark appearing on top of the text.

public function open($attr, &$ahtml, &$ihtml)
{
$txt = '';
if (!empty($attr['CONTENT'])) {
$txt = htmlspecialchars_decode($attr['CONTENT'], ENT_QUOTES);
}

$alpha = -1;
if (isset($attr['ALPHA']) && $attr['ALPHA'] > 0) {
$alpha = $attr['ALPHA'];
}
$this->mpdf->SetWatermarkText($txt, $alpha);
}

public function close(&$ahtml, &$ihtml)
{
}
}

### Understanding the Code:
– **Attributes:**
– `$attr['CONTENT']`: The actual text to be used as a watermark.
– `$attr['ALPHA']`: The transparency level of the watermark (optional).

### Problem:
If your watermark text is showing up on top of the other content (like images or text), it might be because it's being rendered after the rest of your PDF content. The `SetWatermarkText` method in `mPDF` renders the watermark text at the time it is called.

### Solution:
To ensure the watermark is rendered behind all other content, you can use the `SetWatermarkText` method with the option to place it behind the text. In `mPDF`, there is a parameter to set whether the watermark is behind the content or not.

**Adjust your `open()` method as follows:**

class WatermarkText extends Tag
{
    public function open($attr, &$ahtml, &$ihtml)
    {
        $txt = '';
        if (!empty($attr['CONTENT'])) {
            $txt = htmlspecialchars_decode($attr['CONTENT'], ENT_QUOTES);
        }

        $alpha = -1;
        if (isset($attr['ALPHA']) && $attr['ALPHA'] > 0) {
            $alpha = $attr['ALPHA'];
        }

        // Add 'behind' parameter to set watermark behind the content
        $this->mpdf->SetWatermarkText($txt, $alpha);
        $this->mpdf->showWatermarkText = true; // Enable the watermark
        $this->mpdf->watermark_font = 'Helvetica'; // Set font if needed
        $this->mpdf->watermarkTextAlpha = $alpha > 0 ? $alpha : 0.2; // Set the alpha level
        $this->mpdf->watermarkImgBehind = true; // Ensure watermark is behind the content
    }

    public function close(&$ahtml, &$ihtml)
    {
    }
}

### Explanation of Changes:
1. **Set Watermark Behind Content**:

$this->mpdf->watermarkImgBehind = true;

This line ensures that the watermark text appears behind other PDF content.

2. **Set the Alpha Transparency**:

$this->mpdf->watermarkTextAlpha = $alpha > 0 ? $alpha : 0.2;

It uses the provided alpha value or defaults to `0.2` if not set.

3. **Enable the Watermark**:

$this->mpdf->showWatermarkText = true;

This makes sure the watermark text is actually displayed.

### Additional Tips:
– You might need to adjust the `watermark_font` and other properties based on your requirements.
– Ensure this method is called before adding any other content to your PDF if you want the watermark to appear behind everything.

By applying these adjustments, your watermark text should correctly appear behind other elements in your PDF document.