Graph::BackgroundImage PHP Method

    protected function BackgroundImage()
    {
        if (!$this->back_image) {
            return '';
        }
        $image = array('width' => $this->back_image_width, 'height' => $this->back_image_height, 'x' => $this->back_image_left, 'y' => $this->back_image_top, 'xlink:href' => $this->back_image, 'preserveAspectRatio' => $this->back_image_mode == 'stretch' ? 'none' : 'xMinYMin');
        $style = array();
        if ($this->back_image_opacity) {
            $style['opacity'] = $this->back_image_opacity;
        }
        $contents = '';
        if ($this->back_image_mode == 'tile') {
            $image['x'] = 0;
            $image['y'] = 0;
            $im = $this->Element('image', $image, $style);
            $pattern = array('id' => $this->NewID(), 'width' => $this->back_image_width, 'height' => $this->back_image_height, 'x' => $this->back_image_left, 'y' => $this->back_image_top, 'patternUnits' => 'userSpaceOnUse');
            // tiled image becomes a pattern to replace background colour
            $this->defs[] = $this->Element('pattern', $pattern, NULL, $im);
            $this->back_colour = "url(#{$pattern['id']})";
        } else {
            $im = $this->Element('image', $image, $style);
            $contents .= $im;
        }
        return $contents;
    }