PHP Cookbook

15.9. Program: Generating Bar Charts from Poll Results

When displaying the results of a poll, it can be more effective to generate a colorful bar chart instead of just printing the results as text. The function shown in Example 15-4 uses GD to create an image that displays the cumulative responses to a poll question.

Example 15-4. Graphical bar charts

function pc_bar_chart($question, $answers) { // define colors to draw the bars $colors = array(array(255,102,0), array(0,153,0), array(51,51,204), array(255,0,51), array(255,255,0), array(102,255,255), array(153,0,204)); $total = array_sum($answers['votes']); // define some spacing values and other magic numbers $padding = 5; $line_width = 20; $scale = $line_width * 7.5; $bar_height = 10; $x = $y = $padding; // allocate a large palette for drawing, since we don't know // the image length ahead of time $image = ImageCreate(150, 500); $bg_color = ImageColorAllocate($image, 224, 224, 224); $black = ImageColorAllocate($image, 0, 0, 0); // print the question $wrapped = explode("\n", wordwrap($question, $line_width)); foreach ($wrapped as $line) { ImageString($image, 3, $x, $y , $line, $black); $y += 12; } $y += $padding; // print the answers for ($i = 0; $i < count($answers['answer']); $i++) { // format percentage $percent = sprintf('%1.1f', 100*$answers['votes'][$i]/$total); $bar = sprintf('%d', $scale*$answers['votes'][$i]/$total); // grab color $c = $i % count($colors); // handle cases with more bars than colors $text_color = ImageColorAllocate($image, ...