[php] How to draw a graph in PHP?

Hey I want to draw a graph(Stdent mark distribution) in my site based on PHP. How can I do this?

<?
# ------- The graph values in the form of associative array
$values=array(
    "Jan" => 110,
    "Feb" => 130,
    "Mar" => 215,
    "Apr" => 81,
    "May" => 310,
    "Jun" => 110,
    "Jul" => 190,
    "Aug" => 175,
    "Sep" => 390,
    "Oct" => 286,
    "Nov" => 150,
    "Dec" => 196
);


$img_width=450;
$img_height=300; 
$margins=20;


# ---- Find the size of graph by substracting the size of borders
$graph_width=$img_width - $margins * 2;
$graph_height=$img_height - $margins * 2; 
$img=imagecreate($img_width,$img_height);


$bar_width=20;
$total_bars=count($values);
$gap= ($graph_width- $total_bars * $bar_width ) / ($total_bars +1);


# -------  Define Colors ----------------
$bar_color=imagecolorallocate($img,0,64,128);
$background_color=imagecolorallocate($img,240,240,255);
$border_color=imagecolorallocate($img,200,200,200);
$line_color=imagecolorallocate($img,220,220,220);

# ------ Create the border around the graph ------

imagefilledrectangle($img,1,1,$img_width-2,$img_height-2,$border_color);
imagefilledrectangle($img,$margins,$margins,$img_width-1-$margins,$img_height-1-$margins,$background_color);


# ------- Max value is required to adjust the scale -------
$max_value=max($values);
$ratio= $graph_height/$max_value;


# -------- Create scale and draw horizontal lines  --------
$horizontal_lines=20;
$horizontal_gap=$graph_height/$horizontal_lines;

for($i=1;$i<=$horizontal_lines;$i++){
    $y=$img_height - $margins - $horizontal_gap * $i ;
    imageline($img,$margins,$y,$img_width-$margins,$y,$line_color);
    $v=intval($horizontal_gap * $i /$ratio);
    imagestring($img,0,5,$y-5,$v,$bar_color);

}


# ----------- Draw the bars here ------
for($i=0;$i< $total_bars; $i++){ 
    # ------ Extract key and value pair from the current pointer position
    list($key,$value)=each($values); 
    $x1= $margins + $gap + $i * ($gap+$bar_width) ;
    $x2= $x1 + $bar_width; 
    $y1=$margins +$graph_height- intval($value * $ratio) ;
    $y2=$img_height-$margins;
    imagestring($img,0,$x1+3,$y1-10,$value,$bar_color);imagestring($img,0,$x1+3,$img_height-15,$key,$bar_color);        
    imagefilledrectangle($img,$x1,$y1,$x2,$y2,$bar_color);
}
header("Content-type:image/png");
imagepng($img);
$_REQUEST['asdfad']=234234;

?>

You can use google's chart api to generate charts.

By far the easiest solution is to just use the Google Chart API http://code.google.com/apis/chart/

You can make bar graphs, pie charts, use 3D, and it's as easy as building a url with some parameters. See the simple example below.

Have no idea about gd2, but I have done a similar thing with gd and it was not that hard.

Go to http://www.php.net/ and search for things like

• ImageCreate
• imageline
• imagestring

It's not as flashy as some of those other solution out there, but since you generate a picture it will work in all browsers. (except lynx... :-) )

/Johan

Update: I nearly forgot, don't use jpeg for this type of pictures. The jpeg artefacts will be really annoying, png is a better solution.

pChart is another great PHP graphing library.

There are a number of libraries available for generating graphs.

• Open Flash Cart - Flash based
• GraPHPite
• JS charts - Javascript based
• Libchart

More are listed above and here.

There are also several graphing libraries available for PHP to make your life simpler. JPGraph is a good (non-free) one.

Your best bet is to look up php_gd2. It's a fairly decent image library that comes with PHP (just disabled in php.ini), and not only can you output your finished images in a couple formats, it's got enough functions that you should be able to do up a good graph fairly easily.

EDIT: it might help if I gave you a couple useful links:

http://www.libgd.org/ - You can get the latest php_gd2 here
http://ca3.php.net/gd - The php_gd manual.