Jumpbug: optional velocity-timed assist

The unduck window is only 2 units, while a 625-ups fall moves ~9.3 units per
66.7 Hz movement command, so pure jumpbug is ~20% reliable at that speed.

- Add Jumpbug -> Assist timing (default off). When the natural next command
  would skip [36,38], pin the post-command ducked distance to 37 by writing
  the vertical velocity for that command. Pure jumpbug remains available with
  the option off.
- Resolve the client local m_vecAbsVelocity (0x11C) via the client datamap
  and the server m_vecAbsVelocity (0x228) via the server datamap.
- Write both the authoritative server velocity (what SetupMove reads through
  GetAbsVelocity) and the local prediction fields, so the next CreateMove sees
  the assisted origin on both sides.
- Do not write the server m_vecVelocity directly: the datamap scan finds two
  same-named entries (0x1C and 0x29C); SetAbsVelocity syncs it after movement.

1 files changed, 21 insertions, 2 deletions

diff --git a/src/server.cpp b/src/server.cpp
index 6feb55b..3766906 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -31,6 +31,8 @@ int g_srv_health = -1;
 int g_srv_maxhealth = -1;
 int g_srv_lifestate = -1;
 int g_srv_modelindex = -1;
+int g_srv_absvelocity = -1;
+int g_srv_velocity = -1;
 static bool g_srv_ready = false;
 static bool g_srv_checked = false;
 
@@ -105,12 +107,14 @@ bool resolve_server_netvars() {
   g_srv_maxhealth = datamap_offset("m_iMaxHealth", FIELD_INTEGER);
   g_srv_lifestate = datamap_offset("m_lifeState", FIELD_CHARACTER);
   g_srv_modelindex = datamap_offset("m_nModelIndex", 7); // FIELD_SHORT
+  g_srv_absvelocity = datamap_offset("m_vecAbsVelocity", 3); // FIELD_VECTOR
+  g_srv_velocity = datamap_offset("m_vecVelocity", 3);       // FIELD_VECTOR
   g_srv_ready = g_srv_health > 0;
   if (g_srv_ready) {
     logf("server datamap (%s): health=%d maxhealth=%d lifeste=%d "
-         "modelindex=%d",
+         "modelindex=%d absvel=%d vel=%d",
          g_server.path.c_str(), g_srv_health, g_srv_maxhealth, g_srv_lifestate,
-         g_srv_modelindex);
+         g_srv_modelindex, g_srv_absvelocity, g_srv_velocity);
     fail_logged = false;
   } else if (!fail_logged) {
     fail_logged = true;
@@ -175,3 +179,18 @@ int server_model_index(void *base) {
     return -1;
   return (int)*(short *)((uintptr_t)base + g_srv_modelindex);
 }
+
+// Set the authoritative vertical velocity of a server entity. m_vecAbsVelocity
+// is what CGameMovement::SetupMove reads through GetAbsVelocity(); writing the
+// networked m_vecVelocity directly is deliberately avoided because the server
+// datamap scan can find a same-named field on another class first. The movement
+// code syncs m_vecVelocity through SetAbsVelocity after the command.
+bool server_set_velocity_z(int idx, float vz) {
+  if (!g_srv_ready || !g_iface.engineserver || g_srv_absvelocity <= 0)
+    return false;
+  void *base = nullptr;
+  if (server_entity_health(idx, nullptr, nullptr, &base) < 0 || !base)
+    return false;
+  *(float *)((uintptr_t)base + g_srv_absvelocity + 8) = vz;
+  return true;
+}