PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Drawing Figures and Graphing Data
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Listing 22.5.1
Continued
// calculate total number of votes so far
$total_votes=0;
while ($row = $result->fetch_object())
{
$total_votes += $row->num_votes;
}
$result->data_seek(0); // reset result pointer
Part 1, shown in Listing 22.5.1, connects to the MySQL database, updates the votes
according to the user’s selection, and gets the stored votes.After you have that information,
you can begin making calculations to draw the graph. Part 2 is shown in Listing 22.5.2.
Listing 22.5.2
show_poll.php—Part 2 Sets Up All the Variables for Drawing
/*******************************************
Initial calculations for graph
*******************************************/
// set up constants
putenv('GDFONTPATH=C:\WINDOWS\Fonts');
$width=500; // width of image in pixels - this will fit in 640x480
$left_margin = 50; // space to leave on left of graph
$right_margin= 50; // ditto right
$bar_height = 40;
$bar_spacing = $bar_height/2;
$font = 'arial';
$title_size= 16; // point
$main_size= 12; // point
$small_size= 12; // point
$text_indent = 10; // position for text labels from edge of image
// set up initial point to draw from
$x = $left_margin + 60; // place to draw baseline of the graph
$y = 50; // ditto
$bar_unit = ($width-($x+$right_margin)) / 100; // one "point" on the graph
// calculate height of graph - bars plus gaps plus some margin
$height = $num_candidates * ($bar_height + $bar_spacing) + 50;
Part 2 sets up some variables that you will use to actually draw the graph.
Working out the values for these sorts of variables can be tedious, but a bit of forethought
about how you want the finished image to look will make the drawing process
much easier.We arrived at the values used here by sketching the desired effect on a piece
of paper and estimating the required proportions.