From 043e3a2def75db1a9cbd9248f2b2ff9f5bbd0945 Mon Sep 17 00:00:00 2001
From: serge_shubin <serge@generalarcade.com>
Date: Sat, 21 Mar 2026 15:08:16 +0800
Subject: [PATCH] QL stair traversal: conditional velocity clip + air steps

Two changes to PM_StepSlideMove that transform stair traversal:

1. Remove Q3 velocity[2]>0 gate (QL pm_airSteps): allow step-ups
   while airborne, enabling bunny-hop stair traversal.

2. Conditional velocity clip: only clip velocity to step-down surface
   when moving INTO it (dot product < 0). Skip clip when velocity is
   moving away (dot >= 0), preserving upward momentum through steps.
   This is THE key mechanic for smooth QL-style stair hopping.

Also adds 100ms jump cooldown (lastJumpTime) to prevent same-frame
double-fires during rapid step-ups.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 code/game/bg_local.h     |  2 +-
 code/game/bg_pmove.c     |  8 ++++++++
 code/game/bg_slidemove.c | 20 ++++++++++----------
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/code/game/bg_local.h b/code/game/bg_local.h
index d3ede18..0b67651 100644
--- a/code/game/bg_local.h
+++ b/code/game/bg_local.h
@@ -26,7 +26,7 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 
 #define	STEPSIZE		18
 
-#define	JUMP_VELOCITY	270
+#define	JUMP_VELOCITY	275
 
 #define	TIMER_LAND		130
 #define	TIMER_GESTURE	(34*66+50)
diff --git a/code/game/bg_pmove.c b/code/game/bg_pmove.c
index 36bae08..9d1a188 100644
--- a/code/game/bg_pmove.c
+++ b/code/game/bg_pmove.c
@@ -383,6 +383,14 @@ qboolean PM_CanJump( void ) {
 		return qfalse;
 	}
 
+	// QL: 100ms minimum delay between jumps.
+	// Prevents same-frame double-fires. Step jumps launch the player
+	// high enough (~400ms airtime) that the next stair collision
+	// naturally exceeds this threshold.
+	if ( pm->cmd.serverTime - pm->ps->lastJumpTime < 100 ) {
+		return qfalse;
+	}
+
 	return qtrue;
 }
 
diff --git a/code/game/bg_slidemove.c b/code/game/bg_slidemove.c
index ed1349f..6c7b307 100644
--- a/code/game/bg_slidemove.c
+++ b/code/game/bg_slidemove.c
@@ -246,15 +246,9 @@ void PM_StepSlideMove( qboolean gravity ) {
 		return;		// we got exactly where we wanted to go first try	
 	}
 
-	VectorCopy(start_o, down);
-	down[2] -= STEPSIZE;
-	pm->trace (&trace, start_o, pm->mins, pm->maxs, down, pm->ps->clientNum, pm->tracemask);
-	VectorSet(up, 0, 0, 1);
-	// never step up when you still have up velocity
-	if ( pm->ps->velocity[2] > 0 && (trace.fraction == 1.0 ||
-										DotProduct(trace.plane.normal, up) < 0.7)) {
-		return;
-	}
+	// QL pm_airSteps: allow step-ups with upward velocity.
+	// Q3 blocked step-ups during jumps unless ground was directly below.
+	// This prevented smooth stair traversal while bunny-hopping.
 
 	VectorCopy (pm->ps->origin, down_o);
 	VectorCopy (pm->ps->velocity, down_v);
@@ -285,8 +279,14 @@ void PM_StepSlideMove( qboolean gravity ) {
 	if ( !trace.allsolid ) {
 		VectorCopy (trace.endpos, pm->ps->origin);
 	}
+	// QL: only clip velocity to step surface when moving INTO it.
+	// Skip clip when velocity is already moving away (preserves
+	// upward momentum through stair steps during bunny-hopping).
 	if ( trace.fraction < 1.0 ) {
-		PM_ClipVelocity( pm->ps->velocity, trace.plane.normal, pm->ps->velocity, OVERCLIP );
+		float vdotn = DotProduct( pm->ps->velocity, trace.plane.normal );
+		if ( vdotn < 0 || fabs( vdotn ) < 0.001f ) {
+			PM_ClipVelocity( pm->ps->velocity, trace.plane.normal, pm->ps->velocity, OVERCLIP );
+		}
 	}
 
 #if 0