Jumpbug: automatic duck+jump on damaging falls

- Predict the landing speed from the current vertical velocity and a swept
  standing-hull ground trace; engage only when it exceeds
  PLAYER_MAX_SAFE_FALL_SPEED.
- Press duck one command before the unduck window so FinishDuck's 36-unit
  origin raise places the feet ~37 units above the floor.
- On the next command release duck and press jump: PlayerMove runs Duck()
  before CheckJumpButton, so FinishUnDuck sets ground, the jump executes, and
  CheckFalling never sees ground for the fall-damage check.
- Measure the per-command fall from consecutive airborne origins instead of a
  fixed tick interval; clear IN_JUMP while waiting so the pogo latch is clear.
- New Movement -> Jumpbug -> Active toggle (default on), config [jumpbug].

1 files changed, 183 insertions, 3 deletions

diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index 4947b18..125d94e 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -166,7 +166,184 @@ static void apply_autostrafe(CUserCmd *cmd, const float *vel) {
   cmd->sidemove = (dx * rx + dy * ry) * 450.0f;
 }
 
-static void do_move(int seq) {
+// ---------------------------------------------------------------------------
+// jumpbug
+// ---------------------------------------------------------------------------
+//
+// Source jumpbug: while falling, hold duck; on the frame where unducking would
+// leave the standing hull within CategorizePosition's 2-unit ground probe,
+// release duck and press jump. PlayerMove calls Duck() before FullWalkMove's
+// CheckJumpButton, so FinishUnDuck -> CategorizePosition sets the ground
+// entity, the jump executes in the same frame, and CheckFalling never sees
+// ground for the fall-damage test.
+//
+// In air, FinishDuck raises the feet by 36 units (the standing hull is 72
+// tall, the duck hull 36). We exploit that as a one-frame phase shift: press
+// duck when the standing distance x to the floor is about `drop` units, so
+// after this frame's fall the ducked feet sit ~37 units above the floor (the
+// middle of the [36, 38] unduck window) and the next frame can jump.
+
+static constexpr float JB_SAFE_FALL = 526.5f;
+static constexpr float JB_GRAVITY = 600.0f;
+static constexpr float JB_DUCK_RAISE = 36.0f;
+
+static int jb_state = 0; // 0 idle, 1 ducked/waiting for the unduck window
+static int jb_local = -1;
+static float jb_prev_z = 0.0f;
+static bool jb_prev_valid = false;
+static bool jb_prev_ducked = false;
+static float jb_drop = 0.0f; // last measured vertical fall per command
+static int jb_logs = 0;
+static bool jb_tracked = false;
+
+static bool game_running() {
+  if (!g_iface.engine)
+    return true;
+  using BoolFn = bool (*)(void *);
+  if (!vfunc<BoolFn>(g_iface.engine, 26)(g_iface.engine))
+    return false;
+  if (vfunc<BoolFn>(g_iface.engine, 84)(g_iface.engine))
+    return false;
+  return true;
+}
+
+static void jumpbug_reset() {
+  jb_state = 0;
+  jb_prev_valid = false;
+  jb_tracked = false;
+}
+
+static bool jumpbug_apply(CUserCmd *cmd, int local, void *ent, int flags,
+                          const float *vel, float frametime) {
+  if (!feature_active(FEAT_JUMPBUG) || !g_iface.engine ||
+      g_net.origin < 0 || g_net.velocity < 0) {
+    jumpbug_reset();
+    return false;
+  }
+  if (!game_running()) {
+    jumpbug_reset();
+    return false;
+  }
+
+  bool onground = (flags & FL_ONGROUND) != 0;
+  bool inwater = (flags & FL_INWATER) != 0;
+  bool ducked = (flags & FL_DUCKING) != 0;
+  uintptr_t e = (uintptr_t)ent;
+  int movetype =
+      g_net.movetype >= 0 ? *(int *)(e + g_net.movetype) : MOVETYPE_WALK;
+
+  if (onground || inwater || movetype != MOVETYPE_WALK ||
+      (g_net.health >= 0 && *(int *)(e + g_net.health) <= 0)) {
+    jumpbug_reset();
+    return false;
+  }
+
+  Vector origin{*(float *)(e + g_net.origin),
+                *(float *)(e + g_net.origin + 4),
+                *(float *)(e + g_net.origin + 8)};
+  float vz = vel[2];
+
+  if (local != jb_local) {
+    jb_local = local;
+    jumpbug_reset();
+    jb_drop = 0.0f;
+    jb_logs = 0;
+  }
+
+  // Measure the previous command's fall. Both endpoints must be airborne and
+  // standing: a duck transition moves the origin by 36 units and would
+  // otherwise look like a huge fall.
+  if (jb_prev_valid && !jb_prev_ducked && !ducked) {
+    float d = jb_prev_z - origin.z;
+    if (d > 0.05f && d < 250.0f)
+      jb_drop = d;
+  }
+  jb_prev_valid = true;
+  jb_prev_z = origin.z;
+  jb_prev_ducked = ducked;
+
+  if (vz > -10.0f) { // not falling
+    jb_state = 0;
+    jb_tracked = false;
+    return false;
+  }
+
+  float x = ground_distance(origin, ent, 2048.0f);
+  if (x < 0.0f) { // no standable surface below
+    jb_state = 0;
+    jb_tracked = false;
+    return false;
+  }
+  float impact = sqrtf(vz * vz + 2.0f * JB_GRAVITY * x);
+  if (impact <= JB_SAFE_FALL + 0.5f) {
+    jb_tracked = false;
+    jb_state = 0;
+    return false;
+  }
+  if (!jb_tracked) {
+    jb_tracked = true;
+    logf("jumpbug: tracking x=%.1f vz=%.1f impact=%.1f", x, vz, impact);
+  }
+
+  if (jb_drop <= 0.05f) {
+    // No measured fall yet. Bias toward the default 15 ms Source tick when
+    // the input frametime is smaller: setting the duck up early leaves us
+    // ducked above the window, where we can wait; setting it up late would
+    // put us below the unduck window and lose the jump.
+    float dt = frametime;
+    if (!(dt > 0.0f && dt < 0.05f) || dt < 0.015f)
+      dt = 0.015f;
+    jb_drop = -vz * dt + 0.5f * JB_GRAVITY * dt * dt;
+    if (jb_drop < 0.05f)
+      jb_drop = 0.05f;
+  }
+
+  int before = cmd->buttons;
+  bool trigger = false;
+
+  if (ducked) {
+    if (x >= JB_DUCK_RAISE && x <= JB_DUCK_RAISE + 2.0f) {
+      // In the window: unduck (CategorizePosition sets ground) and jump in
+      // the same command.
+      cmd->buttons &= ~IN_DUCK;
+      cmd->buttons |= IN_JUMP;
+      trigger = true;
+      jb_state = 0;
+      jb_tracked = false;
+      if (jb_logs < 20) {
+        jb_logs++;
+        logf("jumpbug: trigger x=%.2f drop=%.2f vz=%.1f", x, jb_drop, vz);
+      }
+    } else {
+      // Hold the crouch and wait for the window. Staying ducked is required
+      // for the unduck trick; releasing early would just add a phase shift
+      // and fight a user who is holding crouch.
+      cmd->buttons |= IN_DUCK;
+      jb_state = 1;
+    }
+  } else {
+    if (jb_state == 1)
+      jb_state = 0; // expected to be ducked but is not
+    if (x <= jb_drop + 2.0f) {
+      // Setup frame: raise the feet 36 units here so the next frame starts
+      // near the middle of the unduck window.
+      cmd->buttons |= IN_DUCK;
+      jb_state = 1;
+      if (jb_logs < 20) {
+        jb_logs++;
+        logf("jumpbug: setup x=%.2f drop=%.2f pred=%.2f vz=%.1f", x, jb_drop,
+             x + JB_DUCK_RAISE - jb_drop, vz);
+      }
+    }
+  }
+
+  if (!trigger && (cmd->buttons & IN_JUMP))
+    cmd->buttons &= ~IN_JUMP; // keep the pogo latch clear for the trigger
+
+  return cmd->buttons != before;
+}
+
+static void do_move(int seq, float frametime) {
   static bool g_echo_sent = false;
   if (!g_input || !g_net.ok())
     return;
@@ -206,6 +383,7 @@ static void do_move(int seq) {
   int flags = *(int *)(e + g_net.flags);
   bool onground = (flags & FL_ONGROUND) != 0;
   bool inwater = (flags & FL_INWATER) != 0;
+  const float *vel = (const float *)(e + g_net.velocity);
 
   bool bhop_on = feature_active(FEAT_BHOP);
   bool abh_on = feature_active(FEAT_ABH);
@@ -217,7 +395,6 @@ static void do_move(int seq) {
       lastground = onground;
       return;
     }
-    const float *vel = (const float *)(e + g_net.velocity);
     float speed = sqrtf(vel[0] * vel[0] + vel[1] * vel[1] + vel[2] * vel[2]);
     bool moving = speed > 0.1f;
     bool backmove = false;
@@ -260,6 +437,9 @@ static void do_move(int seq) {
     }
   }
 
+  if (jumpbug_apply(cmd, localIdx, ent, flags, vel, frametime))
+    note_modified(cmd, flags, vel);
+
   if (!feature_active(FEAT_AIMBOT) || !feature_has_bind(FEAT_AIMBOT))
     aimbot_reset_lock();
   if (!feature_active(FEAT_SILENTAIM) || !feature_has_bind(FEAT_SILENTAIM))
@@ -361,7 +541,7 @@ static void hkdPaintTraverseEx(void *self, long panel, bool paintPopups) {
 
 static bool hkdCreateMove(void *self, int seq, float frametime, bool active) {
   bool ret = oCreateMove(self, seq, frametime, active);
-  do_move(seq);
+  do_move(seq, frametime);
 
   // Hook ISurface once: PaintTraverseEx (slot 114) fires every frame; keep
   // DrawPrintText (slot 22) hooked as a fallback text-draw trigger.