How to set color when using imageopenpolygon()

M66 2025-05-29

In PHP, the imageopenpolygon() function is used to draw a polygon on an image. The syntax of this function is as follows:

 bool imageopenpolygon(resource $image, array $points, int $num_points, int $color)

Parameter analysis:

$image : The target image resource, usually created by functions such as imagecreate() or imagecreatefromjpeg() .
$points : an array containing the coordinates of each point of a polygon. Each coordinate consists of two integer values (x and y).
$num_points : The number of vertices of a polygon.
$color : The color used to draw polygons, usually created by imagecolorallocate() or imagecolorallocatealpha() functions.

How to set color parameters?

In the imageopenpolygon() function, the $color parameter determines the fill color of the polygon. If you want to set the color, you first need to use the imagecolorallocate() function to assign a color value. The format of this function is:

 int imagecolorallocate(resource $image, int $red, int $green, int $blue)

Where $image is the target image resource, $red , $green and $blue are the RGB values of the color, respectively, ranging from 0 to 255. Through this function, you can set different colors.

Sample code:

 <?php
// Create a 400x400 Images
$image = imagecreate(400, 400);

// Assign colors
$bg_color = imagecolorallocate($image, 255, 255, 255); // White background
$polygon_color = imagecolorallocate($image, 0, 0, 255); // Blue polygon

// Set the vertices of the polygon
$points = array(
    100, 100,  // point 1 (x1, y1)
    300, 100,  // point 2 (x2, y2)
    350, 250,  // point 3 (x3, y3)
    250, 350,  // point 4 (x4, y4)
    150, 250   // point 5 (x5, y5)
);

// Draw polygons on images
imageopenpolygon($image, $points, count($points) / 2, $polygon_color);

// Output image
header('Content-Type: image/png');
imagepng($image);

// Destroy image resources
imagedestroy($image);
?>

Code parsing:

Create image resource : Create an image of 400x400 pixels through imagecreate() .
Assign colors : Use imagecolorallocate() to assign colors to the background and polygon respectively. The background is white (RGB: 255, 255, 255), and the polygon is blue (RGB: 0, 0, 255).
Draw polygon : Through the imageopenpolygon() function, a polygon is drawn using the set vertex array $points and color $polygon_color .

Notes:

The imageopenpolygon() function does not automatically close the image resources, so the imagedestroy() function needs to be used to destroy the image and free up memory.
To use the transparency effect, you can use imagecolorallocatealpha() to create colors with transparency.

With the above method, you can easily draw polygons with different colors on the image.