PHP: imagecolorallocatealpha

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 which may have a value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.

Returns FALSE if the allocation failed.

Пример 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); ?>

Замечание: Эта функция нуждается в GD версии 2.0.1 или выше.

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);

?>