Watermark Width on a PDF

A customer just brought up an interesting point: since the watermark width (“cell width” in TCPDF terms) is determined by the PDF page width, won’t a line of text be a “little short” (limited) if the watermark is rotated diagonally?

Since it would take a lot of math with a few variables (page size, mainly) to determine the max cell width based on degree of rotation, I just included a new filter in WaterWoo instead. It’s called ‘wwpdf_cell_width’. (Hey, I like math but it’s still really smokey in California and getting hard to think.) The following code is a simple example of an attempt to override the cell width with 300mm, which should work on pages larger than A4. The code includes a fallback if it won’t work.

add_filter( 'wwpdf_cell_width', 'my_custom_cell_width_function', 10, 2 );
function my_custom_cell_width_function( $cell_width, $page_size ) {
    $w = $page_size['w'];
    $h = $page_size['h'];
    $max = ( $w * $w ) + ( $h * $h ); // using Pythagorean max cell width can’t be bigger than diagonal
    $max = sqrt( $max );
    $cell_width = 300; // number of MILLIMETERS you wish your text to span. 
		       // If it goes off the page, unexpected things will happen
    $cell_width = $cell_width > $max ? $max : $cell_width;
    return $cell_width;
}

The filter is included in WaterWoo PDF Premium for WordPress and it applies to the rotatable overlay watermarks. The footer watermark is also rotatable but does not yet include this WP filter hook.