Why when i rotate the image black borders appear? PHP GD

This code gen开发者_运维问答erates two images using GD and rotates one of them. When I rotate the image black borders begin to appear. Anyone have an idea of how to resolve this?

<?php
$im = imagecreatetruecolor(300, 400);
$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 000, 000, 000);
$black1 = imagecolorallocate($im, 001, 001, 001);
$grey = imagecolorallocate($im, 230, 230, 230);
$font_file = './arial.ttf';
$rotate=45;

imagefilledrectangle($im, 0, 0, 300, 400, $black);
imagefilledrectangle($im, 1, 1, 298, 398, $grey);
imagefilledrectangle($im, 49, 69, 251, 271, $black);
imagefilledrectangle($im, 50, 70, 250, 270, $white);
imagefttext($im, 13, 0, 90, 30, $black, $font_file, "Wind Direcction");

$source=imagecreatetruecolor(100, 100);
imagefilledrectangle($source, 0, 0, 100, 100, $white);
$values = array(
           20, 30,  // Point 1 (x, y)
     50, 0,  
           80, 30, 
     65, 30,
     65, 100,
     35, 100,
     35, 30   // Point 7 (x, y)
            );
imagefilledpolygon($source, $values, 7, $black1);
$asd=imagerotate($source, $rotate, 0);
imagecolortransparent($asd, $black);
imageantialias($asd, true);
$insert_x = imagesx($asd); 
$insert_y = imagesy($asd);

if($rotate==0 || $rotate==90 || $rotate==180 || $rotate==270){
 imagecopymerge ( $im , $asd , 100 , 130 , 0 , 0 , $insert_x , $insert_y , 100 );
}
if($rotate==45 || $rotate==135 || $rotate==225 || $rotate==315){
 imagecopymerge ( $im , $asd , 85 , 110 , 0 , 0 , $insert_x , $insert_y , 100 );
}

imageantialias($im, true);
header('Content-Type: image/png');
imagepng($im);
imagedestroy($im);
?>

Looks like the default color of your image is white:

$source=imagecreatetruecolor(100, 100);
imagefilledrectangle($source, 0, 0, 100, 100, $white);

And your transparency is black:

imagecolortransparent($asd, $black);

Try making the transparency white.