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Homephp教程php手册非常精妙的 PHP 递归调用 代码

 

// 定义 PI 一分的角度的值
define("PII", M_PI/180);

// 新建图像资源,并定义其背景为 白色,前景色为 黑色
$im    = imagecreate(670,500);
$white = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
$g     = imagecolorallocate($im, 0x00, 0x00, 0x00);

// 从下面实例化的代码可以得知,初始值 $x, $y, $L, $a 别分为 300, 500, 100, 270
function drawLeaf($g, $x, $y, $L, $a) {
    global $im;
    $B = 50;
    $C = 9;
    $s1 = 2;
    $s2 = 3 ;
    $s3 = 1.2;
    if($L > $s1) {
        // 计算叶子的定位 上面
        $x2  = $x + $L * cos($a * PII);
        $y2  = $y + $L * sin($a * PII);
        $x2R = $x2 + $L / $s2 * cos(($a + $B) * PII);
        $y2R = $y2 + $L / $s2 * sin(($a + $B) * PII);
        $x2L = $x2 + $L / $s2 * cos(($a - $B) * PII);
        $y2L = $y2 + $L / $s2 * sin(($a - $B) * PII);

        // 计算叶子的定位 下面
        $x1  = $x + $L / $s2 * cos($a * PII);
        $y1  = $y + $L / $s2 * sin($a * PII);
        $x1L = $x1 + $L / $s2 * cos(($a - $B) * PII);
        $y1L = $y1 + $L / $s2 * sin(($a - $B) * PII);
        $x1R = $x1 + $L / $s2 * cos(($a + $B) * PII);
        $y1R = $y1 + $L / $s2 * sin(($a + $B) * PII);

        // 别分画叶子的主干以及叶面
        ImageLine($im, (int)$x,  (int)$y,  (int)$x2,  (int)$y2,  $g);
        ImageLine($im, (int)$x2, (int)$y2, (int)$x2R, (int)$y2R, $g);
        ImageLine($im, (int)$x2, (int)$y2, (int)$x2L, (int)$y2L, $g);
        ImageLine($im, (int)$x1, (int)$y1, (int)$x1L, (int)$y1L, $g);
        ImageLine($im, (int)$x1, (int)$y1, (int)$x1R, (int)$y1R, $g);

        // 再次递归调用本身
        drawLeaf($g, $x2,  $y2,  $L / $s3, $a + $C);
        drawLeaf($g, $x2R, $y2R, $L / $s2, $a + $B);
        drawLeaf($g, $x2L, $y2L, $L / $s2, $a - $B);
        drawLeaf($g, $x1L, $y1L, $L / $s2, $a - $B);
        drawLeaf($g, $x1R, $y1R, $L / $s2, $a + $B);
    }
}

// 实例化
drawLeaf($g, 300, 500, 100, 270);
header("Content-type: image/png");
imagepng($im);
?>



在我个人的 PHP 编程经验中,递归调用常常与静态变量使用。静态变量的含义可以参考 PHP 手册。希望下面的代码,会更有利于对递归以及静态变量的理解

header("Content-type: text/plain");
function static_function () {
    static $i = 0;
    if ($i++         echo $i . "\n";
        static_function();
    }
}
static_function();这段代码会如数输出 1 到 10 的数字。在 static_function 函数第二次运行时,变量 i 由于是静态变量,所以仍被保留不被释放,进而可以得到自增的值。




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