How to make a translucent watermark using the CImageHandler library in yii1?

Question

Yii

Good afternoon,
When loading an image, I put a translucent png watermark on it, but for some reason - the entire transparent substrate becomes a white rectangle,

// в поведении загрузки изоражения
public function createWM($image) {
        Yii::app()->ih
            ->load($image)
            ->watermark($_SERVER['DOCUMENT_ROOT'] .
                '/images/wm.png',
                10,
                20,
                CImageHandler::CORNER_RIGHT_TOP)
            ->save($image);
    }

The watermark method of the CImageHandler class is called along the chain

public function watermark($watermarkFile, $offsetX, $offsetY, $corner = self::CORNER_RIGHT_BOTTOM, $zoom = false)
  {

    $this->checkLoaded();

    if ($wImg = $this->loadImage($watermarkFile))
    {

      $posX = 0;
      $posY = 0;
                        
      $watermarkWidth = $wImg['width'];
      $watermarkHeight = $wImg['height'];

      if($zoom !== false)
      {
        $dimension = round(max($this->width, $this->height) * $zoom);

        $watermarkHeight = $dimension;
        $watermarkWidth = round($watermarkHeight / $wImg['height'] * $wImg['width']);

        if($watermarkWidth > $dimension)
        {
          $watermarkWidth = $dimension;
          $watermarkHeight = round($watermarkWidth / $wImg['width'] * $wImg['height']);
        }
      }

      switch ($corner)
      {
        case self::CORNER_LEFT_TOP:
          $posX = $offsetX;
          $posY = $offsetY;
          break;
        case self::CORNER_RIGHT_TOP:
          $posX = $this->width - $watermarkWidth - $offsetX;
          $posY = $offsetY;
          break;
        case self::CORNER_LEFT_BOTTOM:
          $posX = $offsetX;
          $posY = $this->height - $watermarkHeight - $offsetY;
          break;
        case self::CORNER_RIGHT_BOTTOM:
          $posX = $this->width - $watermarkWidth - $offsetX;
          $posY = $this->height - $watermarkHeight - $offsetY;
          break;
        case self::CORNER_CENTER:
          $posX = floor(($this->width - $watermarkWidth) / 2);
          $posY = floor(($this->height - $watermarkHeight) / 2);
          break;
        default:
          throw new Exception('Invalid $corner value');
      }

      imagecopyresampled(
        $this->image,
        $wImg['image'],
        $posX,
        $posY,
        0,
        0,
        $watermarkWidth,
        $watermarkHeight,
        $wImg['width'],
        $wImg['height']
      );


      imagedestroy($wImg['image']);

      return $this;
    }
    else
    {
      return false;
    }
  }

Tell me where I screwed up?