imagettfbox

I wrote a simple function that calculates the *exact* bounding box (single pixel precision).

The function returns an associative array with these keys:

left, top:  coordinates you will pass to imagettftext 

width, height: dimension of the image you have to create



<?php

function calculateTextBox($font_size, $font_angle, $font_file, $text) {

  $box   = imagettfbbox($font_size, $font_angle, $font_file, $text);

  if( !$box )

    return false;

  $min_x = min( array($box[0], $box[2], $box[4], $box[6]) );

  $max_x = max( array($box[0], $box[2], $box[4], $box[6]) );

  $min_y = min( array($box[1], $box[3], $box[5], $box[7]) );

  $max_y = max( array($box[1], $box[3], $box[5], $box[7]) );

  $width  = ( $max_x - $min_x );

  $height = ( $max_y - $min_y );

  $left   = abs( $min_x ) + $width;

  $top    = abs( $min_y ) + $height;

  // to calculate the exact bounding box i write the text in a large image

  $img     = @imagecreatetruecolor( $width << 2, $height << 2 );

  $white   =  imagecolorallocate( $img, 255, 255, 255 );

  $black   =  imagecolorallocate( $img, 0, 0, 0 );

  imagefilledrectangle($img, 0, 0, imagesx($img), imagesy($img), $black);

  // for sure the text is completely in the image!

  imagettftext( $img, $font_size,

                $font_angle, $left, $top,

                $white, $font_file, $text);

  // start scanning (0=> black => empty)

  $rleft  = $w4 = $width<<2;

  $rright = 0;

  $rbottom   = 0;

  $rtop = $h4 = $height<<2;

  for( $x = 0; $x < $w4; $x++ )

    for( $y = 0; $y < $h4; $y++ )

      if( imagecolorat( $img, $x, $y ) ){

        $rleft   = min( $rleft, $x );

        $rright  = max( $rright, $x );

        $rtop    = min( $rtop, $y );

        $rbottom = max( $rbottom, $y );

      }

  // destroy img and serve the result

  imagedestroy( $img );

  return array( "left"   => $left - $rleft,

                "top"    => $top  - $rtop,

                "width"  => $rright - $rleft + 1,

                "height" => $rbottom - $rtop + 1 );

}

?>