Spread control: set random_seed after CInput::CreateMove

CInput::CreateMove overwrites cmd->random_seed with MD5_PseudoRandom after
CHLClient::CreateMove returns, so the seed set from the client-mode hook was
being discarded. Hook the IInput vtable slot 3 (CInput::CreateMove), call the
original, then apply the spread seed and update the verified command copy and
CRC. This also keeps all aim/movement edits since the original copies the
command into the verified table.

2 files changed, 58 insertions, 3 deletions

diff --git a/src/cinput.cpp b/src/cinput.cpp
index f4ba322..a75cc4f 100644
--- a/src/cinput.cpp
+++ b/src/cinput.cpp
@@ -74,6 +74,63 @@ void fix_verified_crc(int seq, uint32_t crc) {
 }
 
 // ---------------------------------------------------------------------------
+// CInput::CreateMove hook
+// ---------------------------------------------------------------------------
+//
+// The CHLClient::CreateMove hook runs *inside* CInput::CreateMove. After it
+// returns, CInput::CreateMove overwrites cmd->random_seed with
+// MD5_PseudoRandom(sequence_number), then copies the command into the verified
+// command table. To choose the bullet-spread seed we must hook CInput itself
+// and run after that assignment.
+
+using InputCreateMoveFn = void (*)(void *, int, float, bool);
+static InputCreateMoveFn oInputCreateMove = nullptr;
+
+static void hkdInputCreateMove(void *self, int seq, float frametime,
+                               bool active) {
+  if (oInputCreateMove)
+    oInputCreateMove(self, seq, frametime, active);
+
+  CUserCmd *cmd = get_usercmd(seq);
+  if (!cmd)
+    return;
+  int local = engine_get_local_player();
+  if (local <= 0)
+    return;
+  void *ent = entitylist_get(local);
+  if (!ent)
+    return;
+  if (!spread_control_apply(cmd, ent))
+    return;
+
+  // Keep the verified command copy and its CRC in sync with the modified
+  // random_seed. CInput::CreateMove already copied all other (aim/move) fields.
+  uintptr_t verified = *(uintptr_t *)(g_input + CMDOFF_M_PVERIFIED);
+  if (verified) {
+    CUserCmd *vc =
+        (CUserCmd *)(verified + (size_t)(seq % 90) * VERIFIED_STRIDE);
+    vc->random_seed = cmd->random_seed;
+  }
+  fix_verified_crc(seq, usercmd_checksum(cmd));
+}
+
+static bool install_input_hook() {
+  if (!g_input)
+    return false;
+  void **vt = VTABLE((void *)g_input);
+  if (!vt)
+    return false;
+  constexpr size_t N = 64;
+  void **nvt = new void *[N];
+  memcpy(nvt, vt, N * sizeof(void *));
+  oInputCreateMove = (InputCreateMoveFn)vt[3];
+  nvt[3] = (void *)&hkdInputCreateMove;
+  VTABLE((void *)g_input) = nvt;
+  logf("CInput CreateMove hooked: slot 3 orig=%p", (void *)oInputCreateMove);
+  return true;
+}
+
+// ---------------------------------------------------------------------------
 // CInput discovery: byte-scan of CHLClient::CreateMove prologue
 // ---------------------------------------------------------------------------
 
@@ -135,6 +192,7 @@ bool find_input_global() {
       logf("CInput* = %#lx (ptr var %#lx, vfunc[3] %#lx)", (unsigned long)input,
            (unsigned long)var, (unsigned long)f3);
       g_input = input;
+      install_input_hook();
       return true;
     }
   }
diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index dddcbdc..ee2e990 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -532,9 +532,6 @@ static void do_move(int seq, float frametime) {
         note_modified(cmd, flags, vel);
     }
   }
-
-  if (spread_control_apply(cmd, ent))
-    note_modified(cmd, flags, vel);
 }
 
 // ---------------------------------------------------------------------------