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

504 Chapter 22 Generating Images
The $width variable is the total width of the canvas you will use.You also set up the
left and right margins (with $left_margin and $right_margin, respectively); the “fatness”
and spacing between the bars ($bar_height and $bar_spacing); and the font, font
sizes, and label position ($font, $title_size, $main_size, $small_size, and
$text_indent).
Given these base values, you can then make a few calculations.You want to draw a
baseline that all the bars stretch out from.You can work out the position for this baseline
by using the left margin plus an allowance for the text labels for the x coordinate and
again an estimate from the sketch for the y coordinate.You could get the exact width of
the longest name instead if flexibility is important.
You also work out two important values: first, the distance on the graph that represents
one unit:
$bar_unit = ($width-($x+$right_margin)) / 100;
// one “point” on the graph
This is the maximum length of the bars—from the baseline to the right margin—divided
by 100 because the graph is going to show percentage values.
The second value is the total height that you need for the canvas:
$height = $num_candidates * ($bar_height + $bar_spacing) + 50;
This value is basically the height per bar times the number of bars, plus an extra amount
for the title. Part 3 is shown in Listing 22.5.3.
Listing 22.5.3
Added
show_poll.php —Part 3 Sets Up the Graph, Ready for the Data to Be
/*******************************************
Set up base image
*******************************************/
// create a blank canvas
$im = imagecreatetruecolor($width,$height);
// Allocate colors
$white=imagecolorallocate($im,255,255,255);
$blue=imagecolorallocate($im,0,64,128);
$black=imagecolorallocate($im,0,0,0);
$pink = imagecolorallocate($im,255,78,243);
$text_color = $black;
$percent_color = $black;
$bg_color = $white;
$line_color = $black;
$bar_color = $blue;
$number_color = $pink;
// Create "canvas" to draw on
imagefilledrectangle($im,0,0,$width,$height,$bg_color);