PHP three-dimensional pie chart implementation code_PHP tutorial

After hard work, pie3d is completed, and the good stuff is shared with everyone. However, I am new to PHP and the code may not be refined enough. I hope everyone can give me some advice and work together to improve this program. Remember to notify me (estorm@yeah.net)
+---------------------+
| pie3dfun.php//Public functions |
+------------------------+
define("ANGLE_STEP",5);//Define when drawing an elliptical arc Angle step
function chx_getdarkcolor($img,$clr){//Find the dark color corresponding to $clr
$rgb=imagecolorsforindex($img,$clr);
return array($rgb["red "]/2,$rgb["green"]/2,$rgb["blue"]/2);
}
function chx_getexy($a,$b,$d){//Find the angle Point coordinates on the ellipse corresponding to $d
$d=deg2rad($d);
return array(round($a*Cos($d)),round($b*Sin($d)) );
}
function chx_arc($img,$ox,$oy,$a,$b,$sd,$ed,$clr){//Elliptic arc function
$n=ceil( ($ed-$sd)/ANGLE_STEP);
$d=$sd;
list($x0,$y0)=chx_getexy($a,$b,$d);
for($ i=0;$i<$n;$i++){
$d=($d+ANGLE_STEP)>$ed?$ed:($d+ANGLE_STEP);
list($x,$ y)=chx_getexy($a,$b,$d);
imageline($img,$x0+$ox,$y0+$oy,$x+$ox,$y+$oy,$clr);
$x0=$x;
$y0=$y;
}
}
function chx_sector($img,$ox,$oy,$a,$b,$sd,$ed, $clr){//Drawing fan
$n=ceil(($ed-$sd)/ANGLE_STEP);
$d=$sd;
list($x0,$y0)=chx_getexy( $a,$b,$d);
imageline($img,$x0+$ox,$y0+$oy,$ox,$oy,$clr);
for($i=0;$i< ;$n;$i++){
$d=($d+ANGLE_STEP)>$ed?$ed:($d+ANGLE_STEP);
list($x,$y)=chx_getexy($ a,$b,$d);
imageline($img,$x0+$ox,$y0+$oy,$x+$ox,$y+$oy,$clr);
$x0=$x;
$y0=$y;
}
imageline($img,$x0+$ox,$y0+$oy,$ox,$oy,$clr);
list($x,$ y)=chx_getexy($a/2,$b/2,($d+$sd)/2);
imagefill($img,$x+$ox,$y+$oy,$clr);
}
function chx_sector3d($img,$ox,$oy,$a,$b,$v,$sd,$ed,$clr){//3d sector
chx_sector($img,$ox, $oy,$a,$b,$sd,$ed,$clr);
if($sd<180){
list($R,$G,$B)=chx_getdarkcolor($img, $clr);
$clr=imagecolorallocate($img,$R,$G,$B);
if($ed>180) $ed=180;
list($sx,$sy )=chx_getexy($a,$b,$sd);
$sx+=$ox;
$sy+=$oy;
list($ex,$ey)=chx_getexy($a,$ b,$ed);
$ex+=$ox;
$ey+=$oy;
imageline($img,$sx,$sy,$sx,$sy+$v,$clr);
imageline($img,$ex,$ey,$ex,$ey+$v,$clr);
chx_arc($img,$ox,$oy+$v,$a,$b,$sd ,$ed,$clr);
list($sx,$sy)=chx_getexy($a,$b,($sd+$ed)/2);
$sy+=$oy+$v/2 ;
$sx+=$ox;
imagefill($img,$sx,$sy,$clr);
}
}
function chx_getindexcolor($img,$clr){/ /RBG to index color
$R=($clr>>16) & 0xff;
$G=($clr>>8)& 0xff;
$B=($clr) & 0xff;
return imagecolorallocate($img,$R,$G,$B);
}
?>
+--------------- ----------+
| pie3d.php //Three-dimensional pie chart file|
+-------------------- ------+
require("pie3dfun.php");
$a=150;//Ellipse semi-major axis
$b=50;//Ellipse segment semi-axis
$v=20;//Height of round cake
$font=5;//Font
$ox=5+$a;
$oy=5+$b;
$fw=imagefontwidth ($font);
$fh=imagefontheight($font);

$datLst=array(30,10,20,20,10,20,10,20);//data
$labLst=array("a1","a2","a3","a4","a5","a6","a7","a8");//Tag
$clrLst=array( 0x99ff00,0xff6666,0x0099ff,0xff99ff,0xffff99,0x99ffff,0xff3333,0x009999);
$w=10+$a*2;
$h=10+$b*2+$v+($fh+2 )*count($datLst);
$img=imagecreate($w,$h);
//Convert RGB to index color
for($i=0;$i
$clrbk =imagecolorallocate($img,0xff,0xff,0xff);
$clrt=imagecolorallocate($img,0x00,0x00,0x00);
//Fill the background color
imagefill($img,0,0 ,$clrbk);
//Sum
$tot=0;
for($i=0;$i
$sd=0;
$ed=0;
$ly=10+$b*2+$v;
for($i=0;$i $sd=$ed;
$ed+=$datLst[$i]/$tot*360;
//Draw a round cake
chx_sector3d($img,$ox,$oy,$a,$b,$v,$sd,$ed,$clrLst[$i]);//$sd, $ed,$clrLst[$i]);
//Draw label
imagefilledrectangle($img,5,$ly,5+$fw,$ly+$fh,$clrLst[$i]);
imagerectangle($img,5,$ly,5+$fw,$ly+$fh,$clrt);
imagestring($img,$font,5+2*$fw,$ly,
$labLst[$i].":".$datLst[$i]."(".(round(10000*($datLst[$i]/$tot))/100)."%)",
$clrt);
$ly+=$fh+2;
}
//Output graphics
header("Content-type:image/gif");
imagegif($img );
?>