Php recursive call and use of static variables

Php recursive call and use of static variables

// Draw a beautiful leaf // Define the point of view of PI Define ("PII", M_PI/180 ); // Create an image resource and set the background to White. the foreground color to black. $ Im = imagecreate (670,500 ); $ White = imagecolorallocate ($ im, 0xFF, 0xFF, 0xFF ); $ G = imagecolorallocate ($ im, 0x00, 0x00, 0x00 ); // The Code instantiated below shows that the initial values $ x, $ y, $ L, and $ a are not divided into 300,500,100,270. Function drawLeaf ($ g, $ x, $ y, $ L, $ ){ Global $ im; $ B = 50; $ C = 9; $ S1 = 2; $ S2 = 3; $ S3 = 1.2; If ($ L> $ s1 ){ // Calculate the leaf positioning above $ 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 ); // Calculate the position of the leaf. $ 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 ); // Separate the trunk and leaf area of the leaves 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 ); // Re-recursive call itself 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 ); } } // Instantiate DrawLeaf ($ g, 300,500,100,270 ); Header ("Content-type: image/png "); Imagepng ($ im ); ?> In php programming, recursive calls are often used with static variables. For more information about static variables, see The PHP Manual. We hope the following code will be more conducive to understanding recursive and static variables. Header ("Content-type: text/plain "); Function static_function (){ Static $ I = 0; If ($ I ++ <10 ){ Echo $ I. "\ n "; Static_function (); } } Static_function (); The above code outputs a number ranging from 1 to 10. During the second operation of the static_function, variable I is retained and cannot be released because it is a static variable, so that the auto-increment value can be obtained.