Wednesday, October 28, 2009

Drawing a Polygon








Drawing a Polygon


If you want to draw your own figures, you can trace them together using multiple lines, but there's an easier wayyou can use the imagepolygon function to draw a polygon simply by passing it an array of points. Here's how you use this function in general:



imagepolygon(resource image, array points, int num_points, int color)


This function creates a polygon in image. The points array is a PHP array containing the polygon's vertices (points[0] = x0, points[1] = y0, points[2] = x1, points[3] = y1, and so on). The num_points value holds the total number of points in the polygon, and color is the drawing color you want to use.


For example, here's an array of points, $points, in which every pair of values (array[0] and array[1], array[2] and array[3], and so on) specifies a point on the screen:



$points = array(
    0  => 120, 1  => 60,
    2  => 130, 3  => 60,
    4  => 160, 5  => 80,
    6  => 180, 7  => 20,
    8  => 150, 9  => 40,
    10 => 110, 11 => 10,
    12 => 110, 13 => 80
);


Now we can draw the resulting polygon with imagepolygon:



imagepolygon($image, $points, 7, $draw_color );


The whole example appears in phppolygon.php, Example 6.


Example 6. Drawing polygons, phppolygon.php



<?php
    $points = array(
        0  => 120, 1  => 60,
        2  => 130, 3  => 60,
        4  => 160, 5  => 80,
        6  => 180, 7  => 20,
        8  => 150, 9  => 40,
        10 => 110, 11 => 10,
        12 => 110, 13 => 80
    );

    $image_height = 100;
    $image_width = 300;

    $image = imagecreate($image_width, $image_height);
    $back_color = imagecolorallocate($image, 200, 200, 200);

    $draw_color = imagecolorallocate($image, 0, 0, 0);

    imagepolygon($image, $points, 7, $draw_color );

    header('Content-type: image/jpeg');
    imagejpeg($image);
    imagedestroy($image);
?>



We'll use an HTML document, phppolygon.html, to host the new image:



<HTML>
    <HEAD>
        <TITLE>Drawing polygons</TITLE>
    </HEAD>
    <BODY>
        <CENTER>
            <H1>
                Drawing polygons
            </H1>
            <BR>
            <IMG SRC="phppolygon.php">
        </CENTER>
    </BODY>
</HTML>


The new polygon appears in Figure 7. Very nice.


Figure 7. Drawing a polygon.

[View full size image]









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