Last updated: Sat, 24 Mar 2007

imagecolorallocatealpha

(PHP 4 >= 4.3.2, PHP 5)

imagecolorallocatealpha — Allocate a color for an image

Popis

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.

Seznam parametrů

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.

Návratové hodnoty

A color identifier or FALSE if the allocation failed.

ChangeLog (záznam změn)

Verze	Popis
Prior to 5.1.3	Returns -1 if the allocation failed.

Příklady

Příklad 779. 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);

?>

Výše uvedený příklad vypíše něco jako:

Poznámky

Poznámka: Tato funkce vyžaduje GD 2.0.1 nebo novější (doporučena verze 2.0.28 nebo novější).

Viz také

imagecolorallocate()

imagecolordeallocate()

add a note User Contributed Notes
imagecolorallocatealpha

eric (at) junioronline.us
25-Jan-2006 01:41


If you only wish to extract the alpha value for a color, you can simply extract it like so:



<?php



    $color = imagecolorat($im, 50, 50);

    $alpha = $color >> 24;



?>



It actually shifts off the first 24 bits (where 8x3 are used for each color), and returns the remaining 7 allocated bits (commonly used for alpha)

fchristl at hotmail dot com
19-Sep-2003 12:55


Check out this Source, it's a little funny feature showing you, for what imagecolorallocatealpha() is used:



<?php

$im=imagecreatetruecolor(300,300);

$white=imagecolorallocate($im,255,255,255);

imagefilledrectangle($im,0,0,imagesx($im),imagesy($im),$white);

for($i=0;$i<256;$i=$i+10)

{

$col=imagecolorallocatealpha($im,$i,$i,$i,ceil(rand(0,127)));

imagefilledellipse($im,$i,$i,$i,$i,$col);

}

header("content-type: image/png");

imagepng($im);

?>

add a note

imagecolorat

imagecolorallocate

Last updated: Sat, 24 Mar 2007