Blitzschlag: chains of one cast take separate routes

The chains of a cast share the enemies they have claimed and prefer
unclaimed ones. Each chain keeps its heading and ranks candidates by
distance and turn; a chain's first jump turns away from the directions
the other chains set out in, so they keep fanning out. Jumps reach 75 %
of the cast range.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mods/chainlightning.cpp

@@ -11,14 +11,20 @@
 //
 // This mod keeps all of that and decides:
 // - hits per chain N = 3 + level / 5: the first bolt's [14];
-// - the next target: the nearest enemy within half Blitzschlag's cast range (see
-//   below; the game's own jump search used about 316) that this
-//   chain has not hit yet; else another enemy; else the current target again
-//   (a lone enemy takes all N hits);
+// - the next target: an enemy within 75 % of Blitzschlag's cast range (see
+//   below; the game's own jump search used about 316) that no chain of this
+//   cast has claimed yet, so parallel chains take separate routes; else one
+//   this chain has not hit yet; else another enemy; else the current target
+//   again (a lone enemy takes all N hits). Among those, near and straight
+//   ahead wins: each chain keeps its heading, and a chain's first jump turns
+//   away from the directions the other chains set out in, so the chains keep
+//   fanning out instead of merging again;
 // - chains B = 1 + level / 10: B - 1 more chains start at the first target,
 //   each with a bolt at its own first jump target (created while the first
 //   bolt is set up, as copies of its event; no arc for that first hop).
 
+#include <algorithm>
+#include <cmath>
 #include <cstdint>
 #include <cstring>
 #include <map>
@@ -60,10 +66,10 @@ constexpr int kRaySegments = 20;
 double CastRange() {
     return static_cast<double>(kRaySegmentLength) * kRaySegments;
 }
-// A jump between enemies reaches half as far as the cast (request of
-// 2026-10-17: 900 felt too far for jumps).
+// A jump between enemies reaches 75 % of the cast range (requests: 2026-10-17
+// 900 felt too far, half; 2026-10-18 more room for separate routes, 75 %).
 double JumpRange() {
-    return CastRange() / 2;
+    return CastRange() * 0.75;
 }
 constexpr uint32_t kConstant30 = 0x0088ef18;  // float 30.0, shared by 72 instructions
 constexpr uint32_t kRayRemainingMinusSegment = 0x00526db6;  // fsub [30.0]
@@ -75,8 +81,37 @@ constexpr size_t kCreaturePosition = 0x18;  // 4 dwords, as effects are placed
 constexpr size_t kEventHitsLeft = 14;
 constexpr DWORD kChainLifetimeMs = 10000;
 
+// A direction on the ground (unit vector, world axes).
+struct Direction {
+    double x = 0.0;
+    double y = 0.0;
+};
+
+Direction DirectionBetween(const void* from, const void* to) {
+    const double dx = game::CreatureField(to, game::kCreatureX) - game::CreatureField(from, game::kCreatureX);
+    const double dy = game::CreatureField(to, game::kCreatureY) - game::CreatureField(from, game::kCreatureY);
+    const double length = std::sqrt(dx * dx + dy * dy);
+    return length > 0.0 ? Direction{dx / length, dy / length} : Direction{};
+}
+
+double Dot(Direction a, Direction b) {
+    return a.x * b.x + a.y * b.y;
+}
+
+// The chains of one cast: the enemies they have hit or are jumping to, and the
+// directions the chains set out in, so each chain takes its own route
+// (2026-10-18: "make sure that those multiple chains dont just all follow the
+// same route"; reported in play: with the nearest free enemy only, chains
+// spread at the first jump and then mostly merged again).
+struct Cast {
+    std::vector<uint32_t> claimed;
+    std::vector<Direction> starts;
+};
+
 struct Chain {
+    std::shared_ptr<Cast> cast;
     std::vector<uint32_t> hit;  // targets in order
+    Direction heading;          // the last jump's direction (0, 0 before the first)
     DWORD started = 0;
 };
 
@@ -118,10 +153,67 @@ unsigned ArtLevel(void* creature, uint16_t art) {
     return entry ? entry[game::kCooldownLevel] + entry[game::kCooldownBonusLevels] : 0;
 }
 
-// The nearest living enemy of `caster` within the jump range of `from`, not
-// `current`; one not in `avoid` if there is any.
-uint32_t Nearest(void* caster, void* from, uint32_t current, const std::vector<uint32_t>& avoid) {
-    return game::NearestHostile(caster, from, JumpRange(), current, avoid.data(), avoid.size());
+bool Contains(const std::vector<uint32_t>& ids, uint32_t id) {
+    return std::find(ids.begin(), ids.end(), id) != ids.end();
+}
+
+// How strongly a jump keeps its direction: an enemy straight behind counts as
+// three times as far as one straight ahead.
+constexpr double kTurnWeight = 2.0;
+
+// The next target of `chain` from `current` (the creature `from`), among the
+// living enemies of `caster` within the jump range:
+// - first enemies no chain of the cast has claimed, then ones this chain has
+//   not hit, then any other;
+// - among those the cheapest: distance * (1 + kTurnWeight * turn), turn 0 for
+//   straight ahead along the chain's heading, 1 for straight back; a chain's
+//   first jump (no heading yet) turns away from the directions the cast's
+//   other chains set out in.
+// Claims it for the cast and turns the chain's heading towards it; 0 if none.
+uint32_t NextOf(Chain& chain, void* caster, void* from, uint32_t current) {
+    const bool first = chain.heading.x == 0.0 && chain.heading.y == 0.0;
+    uint32_t best = 0;
+    int bestTier = 3;
+    double bestCost = 0.0;
+    Direction bestDirection;
+    const int count = game::NearbyCreatureCount();
+    for (int i = 0; i < count; ++i) {
+        const uint32_t id = game::NearbyCreatureId(i);
+        void* creature = game::GetCreature(id);
+        if (id == current || !creature || game::IsPlayerHeroId(id) || !game::IsHostileTo(caster, creature)) {
+            continue;
+        }
+        const double distance = game::DistanceTo(from, id);
+        if (distance > JumpRange()) {
+            continue;
+        }
+        const int tier = !Contains(chain.cast->claimed, id) ? 0 : !Contains(chain.hit, id) ? 1 : 2;
+        const Direction direction = DirectionBetween(from, creature);
+        double turn = 0.0;
+        if (!first) {
+            turn = (1.0 - Dot(chain.heading, direction)) / 2.0;
+        } else {
+            for (const Direction start : chain.cast->starts) {
+                turn = std::max(turn, (1.0 + Dot(start, direction)) / 2.0);
+            }
+        }
+        const double cost = distance * (1.0 + kTurnWeight * turn);
+        if (best && (tier > bestTier || (tier == bestTier && cost >= bestCost))) {
+            continue;
+        }
+        best = id;
+        bestTier = tier;
+        bestCost = cost;
+        bestDirection = direction;
+    }
+    if (best) {
+        chain.cast->claimed.push_back(best);
+        if (first) {
+            chain.cast->starts.push_back(bestDirection);
+        }
+        chain.heading = bestDirection;
+    }
+    return best;
 }
 
 void Forget() {
@@ -187,19 +279,23 @@ void BeforeFxEvent(uint8_t* fx, uint32_t* event) {
     const uint32_t hits = Hits(level);
     const unsigned chains = Chains(level);
     event[kEventHitsLeft] = hits;
+    auto cast = std::make_shared<Cast>();
+    cast->claimed.push_back(target);
     auto chain = std::make_shared<Chain>();
+    chain->cast = cast;
     chain->hit.push_back(target);
+    chain->heading = DirectionBetween(caster, first);
+    cast->starts.push_back(chain->heading);  // the other chains fan away from it
     chain->started = GetTickCount();
     g_bolts[id] = {chain, hits};
     // More chains: each starts with a bolt at its own first jump target.
-    std::vector<uint32_t> taken{target};
     for (unsigned c = 1; c < chains && hits > 1; ++c) {
-        const uint32_t next = Nearest(caster, first, target, taken);
-        const uint32_t branchTarget = next ? next : target;
-        taken.push_back(branchTarget);
         auto branch = std::make_shared<Chain>();
+        branch->cast = cast;
         branch->hit.push_back(target);
         branch->started = chain->started;
+        const uint32_t next = NextOf(*branch, caster, first, target);
+        const uint32_t branchTarget = next ? next : target;
         g_pending.push_back({branch, branchTarget});
         SpawnBolt(fx, event, branchTarget, hits - 1);
     }
@@ -264,7 +360,7 @@ uint32_t __fastcall NextTarget(void* manager, void*, const int32_t* position, ui
         return 0;
     }
     const std::shared_ptr<Chain> chain = it->second.chain;
-    uint32_t next = Nearest(casterCreature, from, current, chain->hit);
+    uint32_t next = NextOf(*chain, casterCreature, from, current);
     if (!next) {
         next = current;  // nobody else: hit the same enemy again
     }