Programming PHP

Dynamically Generated Buttons

A popular use for dynamically generated images is to create images for buttons on the fly. Normally, a blank button background image is used and text is overlaid on top of it, as shown in Example 9-7.

Example 9-7. Creating a dynamic button

<?php
 $font = 'times';
 if (!$size) $size = 12;
 $im = ImageCreateFromPNG('button.png');
 // calculate position of text
 $tsize = ImageTTFBBox($size,0,$font,$text);
 $dx = abs($tsize[2]-$tsize[0]);
 $dy = abs($tsize[5]-$tsize[3]);
 $x = ( ImageSx($im) - $dx ) / 2;
 $y = ( ImageSy($im) - $dy ) / 2 + $dy;
 // draw text
 $black = ImageColorAllocate($im,0,0,0);
 ImageTTFText($im, $size, 0, $x, $y, $black, $font, $text);
 header('Content-Type: image/png');
 ImagePNG($im);
?>

In this case, the blank button (button.png) looks as shown in Figure 9-6.

Figure 9-6. Blank button

Note that if you are using GD 2.0.1, antialiased TrueType fonts work only if the background image is indexed. If you are having problems with your text looking terrible, load your background image into any image-editing tool and convert it from a true color image to one with an 8-bit indexed palette. Alternatively, upgrade from GD 2.0.1 to GD 2.0.2 or later.

The script in Example 9-7 can be called from a page like this:

<img src="button.php?text=PHP+Button">

This HTML generates the button shown in Figure 9-7.

Figure 9-7. Generated button

The + character in the URL ...