Making a function grapher and graph generator with GD

[horsebox]

I just started using GD yesterday and I've been trying to make a decent graph generator but I'm having serious trouble

http://toxicopoeia.com/test.php

I just got a template for a dead basic graph generator and my plan was to modify it and turn it into a proper graph generator and function grapher but I'm stuck. Heres the code.

 

test.php

<? 
function getvars($var)
{
$cleaned = preg_replace("[^A-Za-z 0-9\/]", "", $_POST["$var"]);
return $cleaned;
}

if (isset($_POST['dimensions']) and $_POST['dimensions'] > 0) { $dimensions = (int)$_POST['dimensions']; } else { $dimensions = 10; }
if (isset($_POST['x_property'])) { $x_property = getvars("x_property"); } else { $x_property = "Property"; }
if (isset($_POST['x_unit'])) { $x_unit = getvars("x_unit");  } else { $x_unit = "Unit"; }
if (isset($_POST['y_property'])) { $y_property = getvars("y_property");  } else { $y_property = "Property"; }
if (isset($_POST['y_unit'])) { $y_unit = getvars("y_unit");  } else { $y_unit = "Unit"; }
if (isset($_POST['x_increment']) and $_POST['x_increment'] > 0) { $x_increment = (int)$_POST['x_increment']; } else { $x_increment = 1; }
if (isset($_POST['y_increment']) and $_POST['y_increment'] > 0) { $y_increment = (int)$_POST['y_increment']; } else { $y_increment = 1; }
if (isset($_POST['x_start']) and $_POST['x_start'] > 0) { $x_start = (int)$_POST['x_start']; } else { $x_start = 1; }
if (isset($_POST['x_end']) and $_POST['x_end'] > 0) { $x_end = (int)$_POST['x_end']; } else { $x_end = $dimensions; }
if (isset($_POST['y_start']) and $_POST['y_start'] > 0) { $y_start = (int)$_POST['y_start']; } else { $y_start = 1; }
if (isset($_POST['y_end']) and $_POST['y_end'] > 0) { $y_end = (int)$_POST['y_end']; } else { $y_end = $dimensions; }

echo '
<form action="test.php" method="post" name="graph">
Dimensions <input type="text" name="dimensions" size="2" maxlength="2" value=' . $dimensions . '><br>
X Property <input type="text" name="x_property" size="10" maxlength="15" value=' . $x_property . '> Unit <input type="text" name="x_unit" size="5" maxlength="10" value=' . $x_unit . '><br>
Y Property <input type="text" name="y_property" size="10" maxlength="15" value=' . $y_property . '> Unit <input type="text" name="y_unit" size="5" maxlength="10" value=' . $y_unit . '><br>
X-Range <input type="text" name="x_start" size="2" maxlength="2" value=' . $x_start . '> to <input type="text" name="x_end" size="2" maxlength="2" value=' . $x_end . '><br>
Y-Range <input type="text" name="y_start" size="2" maxlength="2" value=' . $y_start . '> to <input type="text" name="y_end" size="2" maxlength="2" value=' . $y_end . '><br>
X-Increment <input type="text" name="x_increment" size="2" maxlength="2" value=' . $x_increment . '><br>
Y-Increment <input type="text" name="y_increment" size="2" maxlength="2" value=' . $y_increment . '><br>
<input type="submit" name="go"></form><br>
<img src="grid2.php?dimensions='; 
echo "$dimensions&points=$points&x_property=$x_property&x_unit=$x_unit&y_property=$y_property&y_unit=$y_unit
&x_increment=$x_increment&y_increment=$y_increment&x_start=$x_start&x_end=$x_end&y_start=$y_start&y_end=$y_end&font=Abbeyline.ttf"; echo '" /><br><br>';

?>

 

grid2.php:

$dimensions = (int)$_GET['dimensions']; 
$x_increment = (int)$_GET['x_increment']; 
$y_increment = (int)$_GET['y_increment'];
$x_property = getvars("x_property"); 
$x_unit = getvars("x_unit"); 
$y_property = getvars("y_property"); 
$y_unit = getvars("y_unit"); 

$dim = $dimensions * 25;
$dim2 = $dim - 1;
$dim3 = $dimensions + 1;
$x_offset2 = 50;
$x_offset = 25;
$y_offset = 7;
$xi = 1;
$yi = $dimensions;


$points = "0 0, 0 0, 1 4, 2 7, 3 8, 4 5, 8 7, 7 15, 25 19";

$p = explode(", ",$points);

$pcount = count($p) - 1; 

for ($i=0; $i<$pcount+1; $i++){
if (isset($p[$i])) { 
	$p2 = explode(" ",$p[$i]); 
	$x[$i] = $p2[0] * 25; 
	$y[$i] = $p2[1] * 25; 
}

}

// Define .PNG image
header("Content-type: image/png");

$imgWidth=$dim + 80;
$imgHeight=$dim + 50;

// Create image and define colors
$image=imagecreate($imgWidth, $imgHeight);
$colorWhite=imagecolorallocate($image, 255, 255, 255);
$colorGrey=imagecolorallocate($image, 192, 192, 192);
$colorBlue=imagecolorallocate($image, 0, 0, 255);
$colorRed=imagecolorallocate($image, 255, 0, 0);
$colorGreen=imagecolorallocate($image, 0, 150, 0);
$colorBlack=imagecolorallocate($image, 0, 0, 0);

// Set the line thickness to 5


// Create border around image
imagesetthickness($image, 3);
imageline($image, $x_offset-1, 0, $x_offset-1, $dim, $colorRed);
imagesetthickness($image, 1);
imageline($image, $x_offset, 0, $dim + $x_offset, 0, $colorBlack);
imageline($image, $dim2 + $x_offset, 0, $dim2 + $x_offset, $dim2, $colorBlack);
imagesetthickness($image, 3);
imageline($image, $x_offset, $dim2, $dim2 + $x_offset, $dim2, $colorBlack);

// Create grid
imagesetthickness($image, 1);
for ($i=1; $i<$dim3; $i++){
// Y Axis
imageline($image, $i*25, 0, $i*25, $dim, $colorBlack);
imagestring($image,3,25,$y_offset-10,$yi,$colorBlack);

// X Axis
imageline($image, $x_offset, $i*25, $dim + $x_offset, $i*25, $colorBlack);
imagestring($image,3,15,$imgHeight-25,0,$colorBlack);
imagestring($image,3,$x_offset2-2,$imgHeight-35,$xi,$colorBlack);


$x_offset2 += 25;
$y_offset += 25;

$xi = $xi + $x_increment;
$yi = $yi - $y_increment;
}

imagestring($image,5,($dim/2)-40,$imgHeight-18,"$x_property ($x_unit)",$colorGreen);

imagestringup($image,5,1,($y_offset/2)+40,"$y_property ($y_unit)",$colorGreen);

// Create line graph

 

imagesetthickness($image, 2);

 

for ($i=2; $i<$pcount; $i++){

imageline($image, $x[$i], ($dim-$y[$i]), $x[$i+1], ($dim-$y[$i+1]), $colorBlue);

 

}

 

// Output graph and clear image from memory

imagepng($image);

imagedestroy($image);[/code]

 

Anyone know a better method of doing this? Sooner or later I'm gonna have to make it display curves rather than just straight lines so in order to do that I'm guessing I have to make a load of tiny lines which contantly change slope as they approach the plotted point. Right now the lines are all made in multiples of 25.