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15.7. Building Dynamic Images

15.7.2. Solution

Load the template image, find the correct position to properly center your text, add the text to the canvas, and send the image to the browser:

// Configuration settings
$image    = ImageCreateFromPNG('button.png');
$text     = $_GET['text'];
$font     = ImagePSLoadFont('Times');
$size     = 24;
$color    = ImageColorAllocate($image,   0,   0,   0); // black
$bg_color = ImageColorAllocate($image, 255, 255, 255); // white

// Print centered text
list($x, $y) = pc_ImagePSCenter($image, $text, $font, $size);
ImagePSText($image, $text, $font, $size, $color, $bg_color, $x, $y);

// Send image
header('Content-type: image/png');
ImagePNG($image);

// Clean up
ImagePSFreeFont($font);
ImageDestroy($image);

15.7.3. Discussion

Building dynamic images with GD is easy; all you need to do is combine a few recipes together. At the top of the code in the Solution, we load in an image from a stock template button; it acts as the background on which we overlay the text. We define the text to come directly from the query string. Alternatively, we can pull the string from a database (in the case of access counters) or a remote server (stock quotes or weather report icons).

After that, we continue with the other settings: loading a font and specifying its size, color, and background color. Before printing the text, however, we need to compute its position; pc_ImagePSCenter( ) from Recipe 15.7 nicely solves this task. Last, we serve the image, and deallocate the font and image from memory.

For example, the following code generates a page of HTML and image tags using dynamic buttons, as shown in Figure 15-9:

<?php
if (isset($_GET['button'])) {

    // Configuration settings
    $image    = ImageCreateFromPNG('button.png');
    $text     = $_GET['button'];      // dynamically generated text
    $font     = ImagePSLoadFont('Times');
    $size     = 24;
    $color    = ImageColorAllocate($image,   0,   0,   0); // black
    $bg_color = ImageColorAllocate($image, 255, 255, 255); // white

    // Print centered text
    list($x, $y) = pc_ImagePSCenter($image, $text, $font, $size);
    ImagePSText($image, $text, $font, $size, $color, $bg_color, $x, $y);

    // Send image
    header('Content-type: image/png');
    ImagePNG($image);

    // Clean up
    ImagePSFreeFont($font);
    ImageDestroy($image);

} else {
?>
<html>
<head>
    <title>Sample Button Page</title>
</head>
<body>
    <img src="<?php echo $_SERVER['PHP_SELF']; ?>?button=Previous" 
         alt="Previous" width="132" height="46">
    <img src="<?php echo $_SERVER['PHP_SELF']; ?>?button=Next" 
         alt="Next"     width="132" height="46">
</body>
</html>
<?php
}
?>
Figure 15-9

Figure 15-9. Sample button page

In this script, if a value is passed in for $_GET['button'], we generate a button and send out the PNG. If $_GET['button'] isn't set, we print a basic HTML page with two embedded calls back to the script with requests for button images — one for a Previous button and one for a Next button. A more general solution is to create a separate button.php page that returns only graphics and set the image source to point at that page.

15.7.4. See Also

Recipe 15.6 for more on drawing text; Recipe 15.7 for more on centering text; an excellent discussion on dynamic image caching in Chapter 9, "Graphics," of Programming PHP, by Kevin Tatroe and Rasmus Lerdorf (O'Reilly).



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