PHP recursive invocation and use of static variables

Draw a very beautiful leaf. Defines the value of the angle of a PI point Define ("PII", m_pi/180); Creates a new image resource and defines its background as white with a foreground color of black $im = Imagecreate (670,500); $white = Imagecolorallocate ($im, 0xFF, 0xFF, 0xFF); $g = Imagecolorallocate ($im, 0x00, 0x00, 0x00); From the code instantiated below you can tell that the initial value $x, $y, $L, $a not divided into 300, 500, 100, 270 function Drawleaf ($g, $x, $y, $L, $a) { Global $im; $B = 50; $C = 9; $s 1 = 2; $s 2 = 3; $s 3 = 1.2; if ($L > $s 1) { Calculate the positioning of the leaves above $x 2 = $x + $L * cos ($a * PII); $y 2 = $y + $L * sin ($a * PII); $x 2R = $x 2 + $L/$s 2 * cos (($a + $B) * PII); $y 2R = $y 2 + $L/$s 2 * sin (($a + $B) * PII); $x 2L = $x 2 + $L/$s 2 * cos (($a-$B) * PII); $y 2L = $y 2 + $L/$s 2 * sin (($a-$B) * PII); Calculate the position of the leaves below $x 1 = $x + $L/$s 2 * cos ($a * PII); $y 1 = $y + $L/$s 2 * sin ($a * PII); $x 1L = $x 1 + $L/$s 2 * cos (($a-$B) * PII); $y 1L = $y 1 + $L/$s 2 * sin (($a-$B) * PII); $x 1R = $x 1 + $L/$s 2 * cos (($a + $B) * PII); $y 1R = $y 1 + $L/$s 2 * sin (($a + $B) * PII); Do not draw the leaves of the trunk and foliage Imageline ($im, (int) $x, (int) $y, (int) $x 2, (int) $y 2, $g); Imageline ($im, (int) $x 2, (int) $y 2, (int) $x 2R, (int) $y 2R, $g); Imageline ($im, (int) $x 2, (int) $y 2, (int) $x 2L, (int) $y 2L, $g); Imageline ($im, (int) $x 1, (int) $y 1, (int) $x 1L, (int) $y 1L, $g); Imageline ($im, (int) $x 1, (int) $y 1, (int) $x 1R, (int) $y 1R, $g); Recursively calls itself again Drawleaf ($g, $x 2, $y 2, $L/$s 3, $a + $C); Drawleaf ($g, $x 2R, $y 2R, $L/$s 2, $a + $B); Drawleaf ($g, $x 2L, $y 2L, $L/$s 2, $a-$B); Drawleaf ($g, $x 1L, $y 1L, $L/$s 2, $a-$B); Drawleaf ($g, $x 1R, $y 1R, $L/$s 2, $a + $B); } } Instantiation of Drawleaf ($g, 300, 500, 100, 270); Header ("Content-type:image/png"); Imagepng ($im); ?> Copy Code In PHP programming, recursive calls are often used with static variables. The meaning of static variables can be referenced in the PHP manual. Hopefully, the following code will be more useful for understanding recursion and static variables. Header ("Content-type:text/plain"); function Static_function () { static $i = 0; if ($i + + < 10) { Echo $i. "\ n"; Static_function (); } } Static_function (); Copy Code The above code will output a number from 1 to 10. When the Static_function function is run for the second time, the variable i is still not released because it is a static variable, and thus the self-increment value can be obtained.

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