imagecolorallocatealpha
(PHP 4 >= 4.3.2, PHP 5)
imagecolorallocatealpha — Allocate a color for an image
Описание
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 .
Список параметров
- 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.
Возвращаемые значения
A color identifier or FALSE if the allocation failed.
Список изменений
| Версия | Описание |
|---|---|
| Prior to 5.1.3 | Returns -1 if the allocation failed. |
Примеры
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);
?>
Результатом выполнения данного примера будет что-то подобное:
Примечания
Замечание: Эта функция нуждается в GD версии 2.0.1 или выше.
- PHP Руководство
- Функции по категориям
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- imagesx
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- imagetruecolortopalette
- imagettfbbox
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- imagetypes
- imagewbmp
- imagewebp
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- iptcembed
- iptcparse
- jpeg2wbmp
- png2wbmp
Коментарии
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 = $color >> 24;
?>
It actually shifts off the first 24 bits (where 8x3 are used for each color), and returns the remaining 7 allocated bits (commonly used for alpha)
If you need to calculate the integer representation of a color with an alpha channel, without initialising an image and using the imagecolorallocatealpha function. Then this function might be of some help:
<?php
function alphaColor($hexColor,$alpha)
{
return bindec(decbin($alpha).decbin(hexdec($hexColor));
}
echo alphaColor("FFFFFF",127);
?>
When working with transparency, avoid imagecreate() and use imagecreatetruecolor() instead. Transparency effects may not work as expected within a palette-based image.