From 164bdcbf3e8ed2b7377351b619150586012e1007 Mon Sep 17 00:00:00 2001
From: salmonik <salmonik@tuta.io>
Date: Mon, 26 Oct 2026 15:56:03 +0100
Subject: Bhop: uni-directional auto-strafe for all movement directions

- derive the desired air direction from the raw W/S/A/D input (view-relative)
- pick the velocity perpendicular that rotates toward that target, so S/A/D
  work instead of only forward and A/D no longer spin in circles
- no keys: accelerate along the crosshair
- menu label now "Uni-directional auto-strafe"; state column moved to x=270
---
 src/hl2h.cpp | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

(limited to 'src/hl2h.cpp')

diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index a451a18..b666585 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -114,6 +114,60 @@ void *entitylist_get(int idx) {
   return vfunc<Fn>(g_iface.entitylist, 3)(g_iface.entitylist, idx);
 }
 
+// Source air-strafe. The movement code caps the *wishspeed* used for the
+// acceleration delta to GetAirSpeedCap() (30) but scales accelspeed by the
+// full wishspeed, then clamps to the delta. Putting wishdir perpendicular to
+// the horizontal velocity makes the delta maximal every tick. We express that
+// world-space direction in the current view basis so the camera is untouched.
+//
+// The perpendicular is chosen so the velocity turns toward the direction the
+// player is actually asking for (W/S/A/D relative to the view), which keeps
+// the feature useful in every direction instead of only forward.
+static void apply_autostrafe(CUserCmd *cmd, const float *vel) {
+  float vx = vel[0], vy = vel[1];
+  float speed = sqrtf(vx * vx + vy * vy);
+  if (speed < 1.0f)
+    return;
+
+  float yaw = cmd->viewangles[1] * PI_F / 180.0f;
+  float cy = cosf(yaw), sy = sinf(yaw);
+  float fx = cy, fy = sy;   // view forward on the XY plane
+  float rx = sy, ry = -cy;  // view right on the XY plane
+
+  // Intended ground-plane direction from the raw movement keys (before we
+  // overwrite them). No keys held -> keep accelerating along current travel.
+  float tx, ty;
+  if (fabsf(cmd->forwardmove) > 0.01f || fabsf(cmd->sidemove) > 0.01f) {
+    tx = fx * cmd->forwardmove + rx * cmd->sidemove;
+    ty = fy * cmd->forwardmove + ry * cmd->sidemove;
+    float tl = sqrtf(tx * tx + ty * ty);
+    tx /= tl;
+    ty /= tl;
+  } else {
+    // No movement keys held: accelerate along the crosshair (a velocity-
+    // relative target would keep rotating with the velocity and circle).
+    tx = fx;
+    ty = fy;
+  }
+
+  // +90 degrees from horizontal velocity ("left" in Source's XY convention);
+  // the other perpendicular is its negation. Pick the side that rotates the
+  // velocity toward the intended direction.
+  float px = -vy / speed, py = vx / speed;
+  float cross = vx * ty - vy * tx; // > 0 => target is left of velocity
+  static int last_side = -1;
+  int side = (cross >= 0.0f) ? -1 : 1;
+  if (fabsf(cross) < 1e-6f) // exactly aligned/opposite: keep previous side
+    side = last_side;
+  last_side = side;
+
+  float dx = (side < 0) ? px : -px;
+  float dy = (side < 0) ? py : -py;
+  // 450 saturates the usercmd move clamps and the engine's air-accel cap.
+  cmd->forwardmove = (dx * fx + dy * fy) * 450.0f;
+  cmd->sidemove = (dx * rx + dy * ry) * 450.0f;
+}
+
 static void do_move(int seq) {
   static bool g_echo_sent = false;
   if (!g_input || !g_net.ok())
@@ -177,6 +231,8 @@ static void do_move(int seq) {
     if (!onground) {
       lastground = false;
       cmd->buttons &= ~IN_JUMP;
+      if (!inwater && bhop_autostrafe_enabled())
+        apply_autostrafe(cmd, vel);
       note_modified(cmd, flags, vel);
     } else if (!lastground) {
       lastground = true;
-- 
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