PHP: imageftbbox

Question

What is the application of a bounding box of a text in PHP imageftbbox?

In the example of the manual, it was used to determine the coordinates for the imagefttext function. Is it necessary? Maybe I am missing something here.

...

// First we create our bounding box
$bbox = imageftbbox(10, 0, $font, 'The PHP Documentation Group');

// This is our cordinates for X and Y
$x = $bbox[0] + (imagesx($im) / 2) - ($bbox[4] / 2) - 5;
$y = $bbox[1] + (imagesy($im) / 2) - ($bbox[5] / 2) - 5;

imagefttext($im, 10, 0, $x, $y, $black, $font, 'The PHP Documentation Group');

...

Answer 1

Flylib has extensive information about imagettfbox().

Here's some relevant information from the linked information:

(image copyright Flylib)

From image above, you can see that there are 4 point with 8 information (as the documentation already stated):

Array information     Bounding box coordinate
===================================================================
    0                 X coordinate of the lower left hand corner
    1                 Y coordinate of the lower left hand corner
    2                 X coordinate of the lower right hand corner
    3                 Y coordinate of the lower right hand corner
    4                 X coordinate of the upper right hand corner
    5                 Y coordinate of the upper right hand corner
    6                 X coordinate of the upper left hand corner
    7                 Y coordinate of the upper left hand corner

Again, as stated by the documentation, this information is relative to text regardless of the angle. Therefore, if you rotate the text to 90 degree clockwise, the bounding box become:

Array information     Bounding box coordinate
===================================================================
    0                 X coordinate of the upper left hand corner
    1                 Y coordinate of the upper left hand corner
    2                 X coordinate of the lower left hand corner
    3                 Y coordinate of the lower left hand corner
    4                 X coordinate of the lower right hand corner
    5                 Y coordinate of the lower right hand corner
    6                 X coordinate of the upper right hand corner
    7                 Y coordinate of the upper right hand corner

Another resources that I believe will help you better grasp the basic idea around bounding box:

• http://ruquay.com/sandbox/imagettf/

Answer 2

the pair of functions imageftbbox and imagettfbbox allow you to know how much space will your text take on an image (the first one is used for free type text and the second for true type text)

this way, if you have an application that generates some images and writes on them variable text (user input or something like this) you can decide how/where to place that text using functions like imagefttext or imagettftext (same difference - the font)

so you can do something like:

$bbox = imagettfbbox(34, 0, 'myriadb.otf', strtoupper($name)); //font size 34, text in a horizontal line, use myriadb.otf as font, the user name as variable text
$text_width = $bbox[2]; // this is how much space the name will take
$margin = (CARD_WIDTH-($text_width))/2; // a constant knowing the width of the resulting card.. this way we will center the name..
imagettftext($image, 34, 0, $margin, $y, $white, 'myriadb.otf', strtoupper($name));// $image resource, 34-same size, same angle, the margin is the the x coordinate, fixed $y, color, font and the same text