[Fix] Fixed ai.relvel(). Also introduced dot product function.

scripts/ai/include/attack_generic.lua

@@ -19,7 +19,7 @@ function atk_g_think()
     range = ai.getweaprange()
 
     -- Shouldn't switch targets if close.
-    if dist > range * atk_changetarget then
+    if dist > 400 and dist > range * atk_changetarget then
       ai.poptask()
       ai.pushtask(0, "attack", enemy)
     end

src/ai.c

@@ -1113,7 +1113,9 @@ static int ai_hyperspace(lua_State* L) {
 /* Get the relative velocity of a pilot. */
 static int ai_relvel(lua_State* L) {
   unsigned int id;
+  double dot, mod;
   Pilot* p;
+  Vec2 vv, pv;
 
   LLUA_MIN_ARGS(1);
 
@@ -1126,7 +1128,15 @@ static int ai_relvel(lua_State* L) {
     return 0;
   }
 
-  lua_pushnumber(L, vect_dist(&cur_pilot->solid->vel, &p->solid->vel));
+  /* Get te projection of target on current velocity. */
+  vect_cset(&vv, p->solid->vel.x - cur_pilot->solid->vel.x,
+      p->solid->vel.y - cur_pilot->solid->vel.y);
+  vect_cset(&pv, p->solid->pos.x - cur_pilot->solid->pos.x,
+      p->solid->pos.y - cur_pilot->solid->pos.y);
+  dot = vect_dot(&pv, &vv);
+  mod = MAX(VMOD(pv), 1.); /* Avoid /0. */
+  
+  lua_pushnumber(L, dot / mod);
   return 1;
 }
 

src/physics.c

@@ -78,7 +78,7 @@ void vect_cadd(Vec2* v, const double x, const double y) {
 void vect_reflect(Vec2* r, Vec2* v, Vec2* n) {
   double dot;
 
-  dot       = (v->x*n->x) + (v->y*n->y);
+  dot       = vect_dot(v, n);
   r->x      = v->x - ((2. * dot) * n->x);
   r->y      = v->y - ((2. * dot) * n->y);
   r->mod    = MOD(r->x, r->y);
@@ -86,6 +86,16 @@ void vect_reflect(Vec2* r, Vec2* v, Vec2* n) {
 
 }
 
+/**
+ * @brief Vector dot product.
+ *    @param a Vector 1 for dot product.
+ *    @param b Vector 2 for dot product.
+ *    @return Dot product of vectors.
+ */
+double vect_dot(Vec2* a, Vec2* b) {
+  return a->x * b->x + a->y * b->y;
+}
+  
 /* ================ */
 /* SOLID! */
 /* ================ */
@@ -236,6 +246,5 @@ Solid* solid_create(const double mass, const double dir,
 /* Free an existing solid. */
 void solid_free(Solid* src) {
   free(src);
-  src = NULL;
 }
 

src/physics.h

@@ -34,6 +34,7 @@ void vectnull(Vec2* v);
 double vect_angle(const Vec2* ref, const Vec2* v);
 void vect_cadd(Vec2* v, const double x, const double y);
 void vect_reflect(Vec2* r, Vec2* v, Vec2* n);
+double vect_dot(Vec2* a, Vec2* b);
 
 /* Describe any solid in 2D space. */
 typedef struct Solid_ {