ESP: classify NPC damage immunity/armour/vulnerability

- Resolve server m_takedamage (DAMAGE_NO/DAMAGE_EVENTS_ONLY = immune).
- Classify gunship/strider/dropship as ARMORED (OnTakeDamage only accepts
  DMG_BLAST; only the RPG passes), and headcrab/antlion/manhack as VULN
  (gravity gun / physics impact).
- ESP draws ARMORED/VULN/IMMUNE tags above the name (new "Damage tags"
  toggle, [esp] dmg).
- Aimbot, silent aim, triggerbot and melee skip immune targets and armoured
  targets unless the active weapon is the RPG.

1 files changed, 69 insertions, 0 deletions

diff --git a/src/esp.cpp b/src/esp.cpp
index 4a6b513..aa9f645 100644
--- a/src/esp.cpp
+++ b/src/esp.cpp
@@ -23,6 +23,7 @@ struct EspTarget {
   bool show_health;
   bool friendly;
   bool neutral;
+  int damage; // NpcDamageClass
   char name[48];
 };
 static EspTarget g_targets[128];
@@ -220,6 +221,48 @@ static bool npc_is_friendly(int idx, const char *model, int local_idx,
 }
 
 
+enum NpcDamageClass {
+  NPC_DMG_NORMAL = 0,
+  NPC_DMG_ARMORED,    // only blast damage (RPG) hurts it
+  NPC_DMG_VULNERABLE, // gravity gun / physics damage works well
+  NPC_DMG_IMMUNE      // m_takedamage says no damage at all
+};
+
+static bool model_has(const char *model, const char *needle) {
+  return model && strcasestr(model, needle) != nullptr;
+}
+
+// Server m_takedamage first (authoritative immunity), then the HL2 damage
+// rules for units whose OnTakeDamage filters specific damage types.
+static int npc_damage_class(int idx, const char *model) {
+  int td = server_npc_takedamage(idx);
+  if (td == 0 || td == 1) // DAMAGE_NO / DAMAGE_EVENTS_ONLY
+    return NPC_DMG_IMMUNE;
+  if (model_has(model, "gunship") || model_has(model, "combine_strider") ||
+      model_has(model, "dropship"))
+    return NPC_DMG_ARMORED;
+  if (model_has(model, "headcrab") || model_has(model, "antlion") ||
+      model_has(model, "manhack"))
+    return NPC_DMG_VULNERABLE;
+  return NPC_DMG_NORMAL;
+}
+
+static bool active_weapon_contains(void *local_ent, const char *needle);
+
+// Armoured units need blast damage; the RPG is the only stock weapon that
+// passes their OnTakeDamage filters. Immune units can never be damaged.
+static bool npc_can_be_damaged(int idx, const char *model) {
+  int dc = npc_damage_class(idx, model);
+  if (dc == NPC_DMG_IMMUNE)
+    return false;
+  if (dc != NPC_DMG_ARMORED)
+    return true;
+  int local = engine_get_local_player();
+  void *le = local > 0 ? entitylist_get(local) : nullptr;
+  return active_weapon_contains(le, "rocket_launcher") ||
+         active_weapon_contains(le, "rpg");
+}
+
 static void short_name(const char *model, char *out, size_t outn) {
   if (!model) { snprintf(out, outn, "NPC"); return; }
   const char *base = strrchr(model, '/');
@@ -334,6 +377,7 @@ static void esp_collect(int local_idx) {
     bool neutral = false;
     t.friendly = npc_is_friendly(idx, model, local_idx, neutral);
     t.neutral = neutral;
+    t.damage = npc_damage_class(idx, model);
     short_name(model, t.name, sizeof(t.name));
     if (npc && !model) snprintf(t.name, sizeof(t.name), "NPC");
   }
@@ -603,6 +647,8 @@ static bool select_aim_target(const QAngle &view, unsigned bone_mask,
     bool neutral = false;
     if (npc_is_friendly(idx, model, local, neutral) || neutral)
       return false;
+    if (!npc_can_be_damaged(idx, model))
+      return false;
     if (!bones_update(idx, ent))
       return false;
     Vector pts[32];
@@ -682,6 +728,8 @@ static bool select_aim_target(const QAngle &view, unsigned bone_mask,
     bool neutral = false;
     if (npc_is_friendly(idx, model, local, neutral) || neutral)
       continue;
+    if (!npc_can_be_damaged(idx, model))
+      continue;
 
     float maxz = g_net.maxs >= 0 ? *(float *)(e + g_net.maxs + 8) : 72.0f;
     if (!(maxz > 4.0f && maxz < 512.0f))
@@ -1063,6 +1111,8 @@ bool melee_aimbot_apply(CUserCmd *cmd) {
     bool neutral = false;
     if (npc_is_friendly(idx, model, local, neutral) || neutral)
       continue;
+    if (!npc_can_be_damaged(idx, model))
+      continue;
 
     Vector origin{*(float *)(e + g_net.origin),
                   *(float *)(e + g_net.origin + 4),
@@ -1394,6 +1444,8 @@ bool triggerbot_apply(CUserCmd *cmd) {
     bool neutral = false;
     if (npc_is_friendly(idx, model, local, neutral) || neutral)
       return false;
+    if (!npc_can_be_damaged(idx, model))
+      return false;
     cmd->buttons |= IN_ATTACK;
     static int logs = 0;
     if (logs < 5) {
@@ -1517,6 +1569,23 @@ void esp_draw() {
     }
     if (esp_option(ESP_OPT_SHOW_NAME))
       draw_text_col(left, top - 14, t.name, 255, 255, 255);
+    if (esp_option(ESP_OPT_DAMAGE_TAGS)) {
+      const char *tag = nullptr;
+      int tr = 255, tg = 255, tb = 255;
+      if (t.damage == NPC_DMG_ARMORED) {
+        tag = "ARMORED";
+        tr = 255; tg = 170; tb = 60;
+      } else if (t.damage == NPC_DMG_VULNERABLE) {
+        tag = "VULN";
+        tr = 90; tg = 220; tb = 255;
+      } else if (t.damage == NPC_DMG_IMMUNE) {
+        tag = "IMMUNE";
+        tr = 180; tg = 180; tb = 180;
+      }
+      if (tag)
+        draw_text_col(left, top - (esp_option(ESP_OPT_SHOW_NAME) ? 28 : 14),
+                      tag, tr, tg, tb);
+    }
   }
 
   // Groundwork probe: HL2H_BONE_DEBUG=1 draws a white marker at each NPC's