php gd sets text to center

In web development, adding some text to pictures is a very common requirement. If you want the text to be displayed in the center, you need to set up the gd library in php accordingly.

PHP GD library is a graphics processing library for PHP, which can be used to create and manipulate images. Through the GD library, we can add text, draw lines, draw graphics and a series of operations on pictures to achieve customized picture requirements. In these operations, the center display of text is a very common requirement. Let’s introduce how to set the center display of text in the GD library.

The first thing to make clear is that the functions provided by the GD library to add text are imagestring() and imagestringup(). The function of these two functions is to add strings to the image so that the strings are rendered according to the specified font and font size. Here we mainly introduce how to use imagestring().

imagestring() The syntax format of the function is as follows:

bool imagestring ( resource $image , int $font , int $x , int $y , string $string , int $color )

Among them, $image represents the image resource, $font represents the font size, $x and $y represents the position of the upper left corner of the character in the image, $string represents the string to be output, and $color represents the color of the string.

The following is a specific example code that can display a string in the center of the picture:

<?php
// 定义文本信息
$text = "Hello World!";

// 定义字体大小
$fontsize = 20;

// 获取字体的宽度和高度
$fontwidth = imagefontwidth($fontsize);
$fontheight = imagefontheight($fontsize);

// 定义图片的宽度和高度
$imageWidth = strlen($text) * $fontwidth;
$imageHeight = $fontheight;

// 创建一个指定大小的画布
$image = imagecreate($imageWidth, $imageHeight);

// 设置背景颜色
$bgColor = imagecolorallocate($image, 255, 255, 255);

// 设置文本颜色
$textColor = imagecolorallocate($image, 0, 0, 0);

// 计算文本的 X 和 Y 坐标
$textX = ($imageWidth - strlen($text) * $fontwidth) / 2;
$textY = ($imageHeight - $fontheight) / 2;

// 在画布上添加文本
imagestring($image, $fontsize, $textX, $textY, $text, $textColor);

// 输出图像
header('Content-Type: image/png');
imagepng($image);

// 释放内存
imagedestroy($image);
?>

In this example code, we first define the string to be added and the font size . Next, the width and height of the font are calculated through the functions imagefontwidth() and imagefontheight() to determine the size of the image and the position of the text. Then, we create a canvas of the specified size and set the background color and text color. Finally, the text is added to the canvas through the function imagestring(). It should be noted that when we calculate the X and Y coordinates of the text, we use the following formula:

$textX = ($imageWidth - strlen($text) * $fontwidth) / 2;
$textY = ($imageHeight - $fontheight) / 2;

The function of this formula is to calculate the center position of the text in the canvas. First calculate the width occupied by all text, then subtract the width of the image, and divide the remaining width by 2 to get the X coordinate of the text. In the same way, by calculating the coordinates of the text on the Y-axis, the centered display of the string can be achieved.

It should be noted that if you want to adjust the font style and color, you can modify it through the relevant API. In this example, we use the imagecolorallocate() function to set the text and background colors. In specific actual projects, we can make adjustments according to specific needs.

In short, setting text centering in the GD library is not very complicated. This requirement can be easily achieved by properly calculating the position of the text and using related functions. I hope the above content is helpful to everyone.

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