add pseudo-working anaconda program and intersect() function

c/anaconda.c

@@ -0,0 +1,156 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <math.h>
+#include <time.h>
+
+#include <X11/Xlib.h>
+
+typedef struct point {
+  double x;
+  double y;
+  struct point *next;
+} point;
+
+typedef struct anaconda {
+  int score;
+  double rot;
+  struct point *chain;
+} anaconda;
+
+Display *d;
+Window w;
+XEvent e;
+int s;
+GC gc;
+
+void xinit(void) {
+  d = XOpenDisplay(NULL);
+  s = DefaultScreen(d);
+  w = XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, 100, 100, 1,
+      BlackPixel(d, s), WhitePixel(d, s));
+  XSelectInput(d, w, ExposureMask | KeyPressMask | PointerMotionMask);
+  XMapWindow(d, w);
+  gc = XCreateGC(d, w, 0, NULL);
+}
+
+/* thanks to
+ * https://stackoverflow.com/questions/3838329/how-can-i-check-if-two-segments-intersect/9997374#9997374
+ * for functions ccw and intersect
+*/
+
+int ccw(point *a, point *b, point *c) {
+  return (c->y - a->y) * (b->x - a->x) >
+    (b->y - a->y) * (c->x - a->x);
+}
+
+int intersect(point *a, point *b, point *c, point *d) {
+  return (ccw(a, c, d) != ccw(b, c, d)) && (ccw(a, b, c) != ccw(a, b, d));
+}
+
+point *mkPoint(double x, double y) {
+  point *ret = malloc(sizeof ret);
+
+  ret->x = x;
+  ret->y = y;
+  ret->next = NULL;
+
+  return ret;
+}
+
+point *rotate(point *p, double rot) {
+  double rad = rot * M_PI/180;
+
+  return mkPoint(
+    p->x * cos(rad) - p->y * sin(rad),
+    p->x * sin(rad) + p->y * cos(rad)
+  );
+}
+
+void appendPoint(point *dest, point *origin) {
+  while(dest->next) dest = dest->next;
+  dest->next = origin;
+}
+
+void updateAnaconda(anaconda *anaconda) {
+  point *prev = anaconda->chain;
+  point *temp = rotate(mkPoint(10, 0), anaconda->rot);
+  point *new = mkPoint(
+    prev->x + temp->x,
+    prev->y + temp->y
+  );
+  new->next = prev;
+  anaconda->chain = new;
+
+  free(temp);
+
+  point *traverser = new;
+
+  while(1) {
+    if(traverser->next) {
+      if(traverser->next->next) {
+        traverser = traverser->next;
+      } else break;
+    } else break;
+  }
+  free(traverser->next);
+  traverser->next = NULL;
+}
+
+point *generateChain(int length) {
+  point *ret = mkPoint(100, 100);
+  point *head = ret;
+
+  for(int i = 1; i < length - 1; i++) {
+    ret->next = mkPoint(
+      10 * i + 100,
+      5 * i + 100
+    );
+    ret = ret->next;
+  }
+
+  return head;
+}
+
+anaconda *mkAnaconda(point *point, double rot) {
+  anaconda *ret = malloc(sizeof ret);
+
+  ret->chain = point;
+  ret->rot = rot;
+  ret->score = 0;
+
+  return ret;
+}
+
+int main(void) {
+  anaconda *anaconda = mkAnaconda(generateChain(10), 0);
+  xinit();
+  while(1) {
+    updateAnaconda(anaconda);
+    XClearWindow(d, w);
+    point *ptr = anaconda->chain;
+    while(ptr->next) {
+      XDrawLine(d, w, gc, ptr->x, ptr->y, ptr->next->x, ptr->next->y);
+      ptr = ptr->next;
+    }
+    while(XPending(d)) {
+      XNextEvent(d, &e);
+      switch(e.type) {
+        case KeyPress:
+          switch(e.xkey.keycode) {
+            case 113: /* left arrow key */
+              anaconda->rot += 10;
+              break;
+            case 114: /* right arrow key */
+              anaconda->rot -= 10;
+              break;
+          }
+          break;
+      }
+    }
+    usleep(100000);
+  }
+
+  return 0;
+}