PHP: Allocate a color for an image

Description

int imagecolorallocatealpha ( resource $image , int $red , int $green , int $blue , int $alpha )

imagecolorallocatealpha() behaves identically to imagecolorallocate() with the addition of the transparency parameter alpha .

Parameters

image: An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
red: Value of red component
green: Value of green component
blue: Value of blue component
alpha: A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.

The colors parameters are integers between 0 and 255 or hexadecimals between 0x00 and 0xFF.

Return Values

A color identifier or FALSE if the allocation failed.

ChangeLog

Version Description

Prior to 5.1.3 Returns -1 if the allocation failed.

Examples

Example #1 Example of using imagecolorallocatealpha()


<?php

$size = 300;

$image=imagecreatetruecolor($size, $size);



// something to get a white background with black border

$back = imagecolorallocate($image, 255, 255, 255);

$border = imagecolorallocate($image, 0, 0, 0);

imagefilledrectangle($image, 0, 0, $size - 1, $size - 1, $back);

imagerectangle($image, 0, 0, $size - 1, $size - 1, $border);



$yellow_x = 100;

$yellow_y = 75;

$red_x    = 120;

$red_y    = 165;

$blue_x   = 187;

$blue_y   = 125;

$radius   = 150;



// allocate colors with alpha values

$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);

$red    = imagecolorallocatealpha($image, 255, 0, 0, 75);

$blue   = imagecolorallocatealpha($image, 0, 0, 255, 75);



// drawing 3 overlapped circle

imagefilledellipse($image, $yellow_x, $yellow_y, $radius, $radius, $yellow);

imagefilledellipse($image, $red_x, $red_y, $radius, $radius, $red);

imagefilledellipse($image, $blue_x, $blue_y, $radius, $radius, $blue);



// don't forget to output a correct header!

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



// and finally, output the result

imagepng($image);

imagedestroy($image);

?>

The above example will output something similar to:

Notes

Note: This function requires GD 2.0.1 or later (2.0.28 or later is recommended).