Detailed analysis of how to define colors, draw points, lines and rectangles in PHP?

In the previous article, I brought you "How to output pictures in PHP? (Detailed explanation of the legend) ", which introduces in detail how to output images in PHP. This article continues to show you how we should draw images in PHP. I hope it can help you!

Drawing images in PHP is all based on the canvas in the previous article, create the canvas, and then draw the image on the canvas. When we think of images, we think of colors, so first, let's take a look at how we should define colors for images in PHP.

Image definition color

When we use PHP to operate images, it is inevitable to set the color and outline different colors Came out with this beautiful image. So how should we provide color to images in PHP? At this time we will use the two functions imagecolorallocate() and imagecolorallocatealpha(). Next, let's take a look at how to use these two functions.

• imagecolorallocate()Function

imagecolorallocate() function can be used for images Assign colors. If you want to set multiple colors, you need to call this function multiple times. The syntax format of the function is:

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

Among them, $image represents the image whose color needs to be set, and the function will return an identifier. Represents the color composed of the given RGB components. $red, $green and $blue are the red, green and blue components of the required color respectively. The value range is an integer from 0 to 255 or hexadecimal 0x00 to 0xFF.

The example is as follows:

<?php
    $image = imagecreate(100, 100);
    $blue = imagecolorallocate($image, 0, 0, 255);
    header(&#39;Content-type:image/jpeg&#39;);
    imagejpeg($image);
    imagedestroy($image);
?>

Output result:

• ## imagecolorallocatealpha()Function

The imagecolorallocatealpha() function has the same function as the imagecolorallocate() function, but there is one more one for setting The alpha of the transparent parameter, its syntax format is as follows:

imagecolorallocatealpha(resource $image, int $red, int $green, int $blue, int $alpha)

Among them, the previous parameters are consistent with the parameters of the imagecolorallocate() function, $alphab represents the transparency parameter, and the value range is from 0 to Between 127, 0 means completely opaque and 127 means completely transparent.

The example is as follows:

<?php
    $size=300;
    $image=imagecreatetruecolor($size,$size);
    $back=imagecolorallocate($image,0,0,0);
    $border=imagecolorallocate($image,255,255,255);
    imagefilledrectangle($image,0,0,$size-1,$size-1,$back);
    imagerectangle($image,0,0,$size-1,$size-1,$border);
    $yellow_x=100;
    $yellow_y=75;
    $red_x=100;
    $red_y=165;
    $blue_x=187;
    $blue_y=125;
    $radius=150;
    //用alpha值分配一些颜色
    $yellow=imagecolorallocatealpha($image,200,200,0,75);
    $red=imagecolorallocatealpha($image,200,0,0,75);
    $blue=imagecolorallocatealpha($image,0,0,200,75);
    //画3个交迭的圆
    imagefilledellipse($image,$yellow_x,$yellow_y,$radius,$radius,$yellow);
    imagefilledellipse($image,$red_x,$red_y,$radius,$radius,$red);
    imagefilledellipse($image,$blue_x,$blue_y,$radius,$radius,$blue);
    //不要忘记输出正确的header!
    header(&#39;Content-type:image/png&#39;);
    //最后输出结果
    imagepng($image);
    imagedestroy($image);
?>

Output result:

##From this, through imagecolorallocate() and imagecolorallocatealpha() These two functions can already define colors on images. At the same time, images are not only made up of colors, but also dots, lines and different shapes. Then let's take a look at how to solve these problems.

Drawing points and lines
Drawing points and lines can be said to be the most basic operation of drawing images in PHP, although it is very simple. Basic, but with flexible application, more complex images can be drawn through them. We can draw a point in the canvas through the

imagesetpixel()

function, and can also set the color of the point. The syntax of its function The format is as follows: <pre class='brush:php;toolbar:false;'>imagesetpixel(resource $image, int $x, int $y, int $color)</pre> Among them, $image represents the created canvas, $x and $y represent the coordinate point at ($x, $y), and the color of this coordinate point is $color.

To draw a line segment, you can use the

imageline()

function. Its syntax format is as follows: <pre class='brush:php;toolbar:false;'>imageline(resource $image, int $x1, int $y1, int $x2, int $y2, int $color)</pre> Among them, it represents the coordinate ($x1,$y1) A line segment with color $color to coordinates ($x2,$y2).

Next we can give an example by combining loops and random numbers:

<?php
    $img = imagecreate(200, 100);
    imagecolorallocate($img, 0, 0, 0);
    $blue = imagecolorallocate($img, 0, 0, 255);
    $red = imagecolorallocate($img, 255, 0, 0);
    for ($i=0; $i <= 50; $i++) {
        $color = imagecolorallocate($img, rand(0, 255), rand(0, 255), rand(0, 255));
        imagesetpixel($img, rand(0, 200), rand(0, 100), $color);
        imageline($img, rand(0, 200), rand(0, 100), rand(0, 200), rand(0, 100), $color);
    }
    header(&#39;Content-type:image/jpeg&#39;);
    imagejpeg($img);
    imagedestroy($img);
?>

Output result:

Draw a rectangle
In PHP, if we want to draw a rectangle, we need to pass

imagerectangle()

Or imagefilledrectangle() function to perform. The imagefilledrectangle() function fills the rectangle after it is drawn, but the imagerectangle() function does not. Their syntax format is as follows:

imagerectangle(resource $image, int $x1, int $y1, int $x2, int $y2, int $color)
imagefilledrectangle(resource $image, int $x1, int $y1, int $x2, int $y2, int $color)

Among them, both represent drawing a coordinate of the upper left corner ($x1, $y1) and the coordinates of the lower right corner ($x2, $y2). Rectangle, the difference between the two is: the color after the imagerectangle() function represents the color of the rectangle's edges, and the color after the imagefilledrectangle() function represents the fill color within the rectangle.

Next, draw a rectangle through the imagerectangle() or imagefilledrectangle() function through an example. The example is as follows:

<?php
    $img = imagecreate(300, 150);
    imagecolorallocate($img, 255, 255, 255);
    $green = imagecolorallocate($img, 0, 255, 0);
    $blue = imagecolorallocate($img, 0, 0, 255);
    imagerectangle($img, 5, 5, 145, 145, $green);
    imagefilledrectangle($img, 150, 5, 295, 145, $blue);
    header(&#39;Content-type:image/jpeg&#39;);
    imagejpeg($img);
    imagedestroy($img);
?>

Output result:

Recommended learning: "PHP Video Tutorial"

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