How to create transparent background in gd without blurring image? - php

Question

I'm trying to create a pie chart, which will display browser stats.
But, when I try to create a transparent background to chart, text goes blurry than normal background.
define('FONT', "C:/Windows/fonts/Arial.ttf");
$data = ['edge' => 3, 'ie' => 4, 'firefox' => 12, 'chrome' => 40, 'opera' => 9, 'android' => 18];
function textWidth($text, $fontSize) {
$sizes = array_map(function($x){ return $x * .75; }, imagettfbbox($fontSize, 0, FONT, $text));
return $sizes[6] - $sizes[4];
}
asort($data);
$total = array_sum($data);
$before = -90;
$w = 300;
$h = 300;
$graph = imagecreatetruecolor($w * 2, $h * 2);
// this is the part where background blurrs: remove this part to compare
imagealphablending($graph, false);
$transparency = imagecolorallocatealpha($graph, 0, 0, 0, 127);
imagefill($graph, 0, 0, $transparency);
imagesavealpha($graph, true);
//part end
$text_color = imagecolorallocate($graph, 0, 0, 0);
foreach ($data as $key => $value) {
$ratio = 100 / $total * $value;
$deg = $before + 3.6 * $ratio;
$color = imagecolorallocate($graph, rand(128,255), rand(128,255), rand(128,255));
imagefilledarc($graph, $w, $h, $w * 2, $h * 2, $before, $deg, $color, IMG_ARC_PIE);
$posX = $w + $w * cos(deg2rad($deg - 1.8 * $ratio)) * .75;
$posY = $w + $w * sin(deg2rad($deg - 1.8 * $ratio)) * .75;
$ratio = floor($ratio);
imagettftext($graph, 16, 0, $posX + textWidth($key, 18) / 2, $posY, $text_color, FONT, $key);
imagettftext($graph, 16, 0, $posX + textWidth($ratio . "%", 18) / 2, $posY + 30, $text_color, FONT, $ratio . "%");
$before = $deg;
}
header('Content-type: image/png');
imagepng($graph);
imagedestroy($graph);
I've tried to create transparent background after drawing each parts of graph, but it didn't worked.
Any help would be appreciated. Thanks!

Answer 1

You can either remove the following line:
imagealphablending($graph, false);
Or re-enable alpha blending after setting the transparency:
imagealphablending($graph, false);
$transparency = imagecolorallocatealpha($graph, 0, 0, 0, 127);
imagefill($graph, 0, 0, $transparency);
imagealphablending($graph, true); // add this
imagesavealpha($graph, true);
Result: