Detailed explanation of canvas in PHP

This article mainly shares with you the detailed explanation of canvas in PHP and the image processing technology GD in PHP. I hope it can help you.

Create a new canvas--Resource data (can operate image resources)

ImageCreate (canvas width, canvas height); create a palette-based canvas.

ImageCreateTrueColor(canvas width, canvas height); Create a true color canvas.

Create canvas based on image

ImageCreateFromFPG (image address);

ImageCreateFromPNG (image address);

ImageCreateFromGIF (image address);

Operation canvas

Assign color: If you need to use a color on the canvas, you should assign the color to the canvas first.

                                                                                                                                               Graphid:

# ImageFill

Write the string to the canvas:

ImageString (canvas resource, font, position x, position y, string content, character color);

The font is a built-in font, with sizes ranging from 1 to 5.

The character color is the variable written when assigning the previous color.

##:

# iMAGESX; get the width of the canvas.

                 ImageSY (canvas resource); get the height of the canvas.

Get the size of the built-in font:

ImageFontWidth (font number); Get the width of the built-in font.

                     ImageFontHeight (font number); Get the height of the built-in font.

Output canvas

1. Output to image file.

2. Output directly to the page.

ImagePNG(canvas resource[, file address]);

## ImageJPEG(canvas Resource [, file address]);

## ImageGIF(canvas resource[, File address]);

Example: Verification code

##

<?php
header(&#39;Content-Type:image/jpg&#39;);
$chars=&#39;ABCDEFGHIJKLMNPQRSTUVWXYZ123456789&#39;;
$chars_length=strlen($chars);
$code_length=4;
$code=&#39;&#39;;
for($i=0;$i<$code_length;$i++){
	$rand_index=mt_rand(0,$chars_length-1);
	$code.=$chars[$rand_index];
}

//存储于session，用于验证。
session_start();
$_SESSION[&#39;captcha_code&#39;]=$code;


//背景图。
$bg_file=&#39;./captcha/captcha_bg&#39;.mt_rand(1,5).&#39;.jpg&#39;;
$img=ImageCreateFromJPEG($bg_file);
//随机分发颜色
$chars_color=mt_rand(1,2)==1?imagecolorallocate($img,0,0,0):imagecolorallocate($img,255,255,255);
//将字符串写到画布上。
$img_width=ImageSX($img);
$img_height=ImageSY($img);
$font_width=ImageFontWidth(5)*4;
$font_height=ImageFontHeight(5);
$code_width=($img_width-$font_width)/2;
$code_height=($img_height-$font_height)/2;
ImageString($img,5,$code_width,$code_height,$code,$chars_color);
ImageJPEG($img);

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