Let’s have a look at the code so far:
<?php
// Send out the header info and create the initial blank canvas
Header( 'Content-type: image/gif');
$image = imagecreate(200,200);
// Allocate some colors
$red = ImageColorAllocate($image,255,0,0);
$blue = ImageColorAllocate($image,0,0,255);
$white = ImageColorAllocate($image,255,255,255);
$grey = ImageColorAllocate($image,200,200,200);
// create an initial grey rectangle for us to draw on
ImageFilledRectangle($image,0,0,200,200,$grey);
// Connect to the mysql server and select the database
$connect = mysql_connect('','root','');
mysql_select_db('graphing',$connect);
// find out the maximum number in our recordset
$sql = 'SELECT MAX(g_num) FROM sales';
$maxResult = mysql_query($sql,$connect);
$max = mysql_result($maxResult,0,0);
// get the recordset for London
$sql = "SELECT g_num FROM sales WHERE g_team='London' ORDER BY g_month";
$salesResult = mysql_query($sql,$connect);
// find out how many rows were returned, that is the number of 'columns'
$columns = mysql_num_rows($salesResult);
// how much to increment $x by ?
$xincrement = bcdiv(200,$columns-1,0);
$x=0;
// $i will keep track of the row number
$i=0;
// lop around while we have rows of data
while($salesRow=mysql_fetch_array($salesResult)) {
// work out the y co-ordinate as discussed above
$y = bcmul(bcdiv($salesRow[0],$max,2),200,2);
// add the values into the $points array
$points[$i][0] = $x;
$points[$i][1] = $y;
// increment $x by $xincrement
$x+=$xincrement;
// increment $i
$i++;
}
// now we loop around through our $points array, while $i is
// less that $columns-1
for($i=0;$i<$columns-1;$i++) {
// We pass $points[$I][0] as the first x co-ord,
// and $points[$I][1] as the first y co-ord
// $points[$I+1][0], $points[$I+1][1] will be the next
// x,y co-ord set.
ImageLine($image,$points[$i][0],$points[$i][1],$points[$i+1][0],$points[$i+1][1],$red);
}
// output the GIF to the browser and free up memory
ImageGIF($image);
ImageDestroy($image);
?>
This gives us the following result:
which is both wrong and irritating. The problem that we have is that we have been working on the traditional method of x and y co-ordinates that radiate outwards from the bottom left hand corner. The co-ordinate system in the Image functions radiate out from the top left hand corner, so while our x position has been correct, our y position has been mirrored.
