Programming PHP

Creating and Drawing Images

For now, let’s start with the simplest possible GD example. Example 9-1 is a script that generates a black filled square. The code works with any version of GD that supports the PNG image format.

Example 9-1. A black square on a white background (black.php)

<?php
 $im = ImageCreate(200,200);
 $white = ImageColorAllocate($im,0xFF,0xFF,0xFF);
 $black = ImageColorAllocate($im,0x00,0x00,0x00);
 ImageFilledRectangle($im,50,50,150,150,$black);
 header('Content-Type: image/png');
 ImagePNG($im);
?>

Example 9-1 illustrates the basic steps in generating any image: creating the image, allocating colors, drawing the image, and then saving or sending the image. Figure 9-1 shows the output of Example 9-1.

Figure 9-1. A black square on a white background

To see the result, simply point your browser at the black.php PHP page. To embed this image in a web page, use:

<img src="black.php">

The Structure of a Graphics Program

Most dynamic image-generation programs follow the same basic steps outlined in Example 9-1.

You can create a 256-color image with the ImageCreate( ) function, which returns an image handle:

$image = ImageCreate(width, height);

All colors used in an image must be allocated with the ImageColorAllocate( ) function. The first color allocated becomes the background color for the image.^[4]

$color = ImageColorAllocate(image, red, green, blue);

The arguments ...