QL stair momentum: conditional velocity clip + air steps + step jump

THE key QL stair mechanic: skip velocity clip in PM_StepSlideMove when
velocity is moving away from the step surface (dot product >= 0). Q3
always clips, zeroing vertical momentum on every step. QL preserves
upward velocity through steps, enabling smooth bunny-hop stair traversal.

Also includes:
- Remove Q3 velocity[2]>0 gate (pm_airSteps): allow step-ups during jumps
- pml.isStepJump flag for step jump context in PM_Jump
- PM_Jump: additive velocity for step jumps (+=270, min 270, max 700)
- 100ms jump cooldown via lastJumpTime

Has known glitches — saved for reference before fixing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

code/game/bg_local.h

@@ -51,6 +51,10 @@ typedef struct {
 	vec3_t		previous_origin;
 	vec3_t		previous_velocity;
 	int			previous_waterlevel;
+
+	// QL step jump context flag — set before calling PM_Jump
+	// from PM_StepSlideMove to get additive velocity instead of flat set
+	qboolean	isStepJump;
 } pml_t;
 
 extern	pmove_t		*pm;
@@ -77,6 +81,8 @@ void PM_ClipVelocity( vec3_t in, vec3_t normal, vec3_t out, float overbounce );
 void PM_AddTouchEnt( int entityNum );
 void PM_AddEvent( int newEvent );
 
+qboolean	PM_CanJump( void );
+void		PM_Jump( void );
 qboolean	PM_SlideMove( qboolean gravity );
 void		PM_StepSlideMove( qboolean gravity );
 

code/game/bg_pmove.c

@@ -353,32 +353,71 @@ static void PM_SetMovementDir( void ) {
 
 /*
 =============
-PM_CheckJump
+PM_Jump
+
+Applies jump velocity, event, and animation.
+Extracted from PM_CheckJump so it can be called
+from other contexts (step jump, double jump, etc).
 =============
 */
-static qboolean PM_CheckJump( void ) {
+/*
+=============
+PM_CanJump
+
+Returns qtrue if a jump would succeed right now.
+Checks both player state AND input (upmove >= 10).
+Used by PM_StepSlideMove to decide whether stepping
+up stairs should trigger a jump.
+=============
+*/
+qboolean PM_CanJump( void ) {
 	if ( pm->ps->pm_flags & PMF_RESPAWNED ) {
-		return qfalse;		// don't allow jump until all buttons are up
+		return qfalse;
+	}
+
+	if ( pm->ps->pm_type != PM_NORMAL ) {
+		return qfalse;
 	}
 
 	if ( pm->cmd.upmove < 10 ) {
-		// not holding jump
 		return qfalse;
 	}
 
-	// must wait for jump to be released
+	// QL: 100ms minimum delay between jumps.
-	if ( pm->ps->pm_flags & PMF_JUMP_HELD ) {
+	// Prevents same-frame double-fires. Step jumps launch the player
-		// clear upmove so cmdscale doesn't lower running speed
+	// high enough (~400ms airtime) that the next stair collision
-		pm->cmd.upmove = 0;
+	// naturally exceeds this threshold.
+	if ( pm->cmd.serverTime - pm->ps->lastJumpTime < 100 ) {
 		return qfalse;
 	}
 
+	return qtrue;
+}
+
+void PM_Jump( void ) {
 	pml.groundPlane = qfalse;		// jumping away
 	pml.walking = qfalse;
 	pm->ps->pm_flags |= PMF_JUMP_HELD;
 
 	pm->ps->groundEntityNum = ENTITYNUM_NONE;
+
+	if ( pml.isStepJump ) {
+		// QL step jump: additive velocity, preserving existing upward motion.
+		// This launches the player high enough to skip several stairs,
+		// so the next collision is >100ms away and the cooldown works.
+		pm->ps->velocity[2] += JUMP_VELOCITY;
+		if ( pm->ps->velocity[2] < JUMP_VELOCITY ) {
 			pm->ps->velocity[2] = JUMP_VELOCITY;
+		}
+		if ( pm->ps->velocity[2] > 700 ) {
+			pm->ps->velocity[2] = 700;
+		}
+	} else {
+		// Normal ground jump: flat velocity set (Q3 behavior)
+		pm->ps->velocity[2] = JUMP_VELOCITY;
+	}
+
+	pm->ps->lastJumpTime = pm->cmd.serverTime;
 	PM_AddEvent( EV_JUMP );
 
 	if ( pm->cmd.forwardmove >= 0 ) {
@@ -388,6 +427,23 @@ static qboolean PM_CheckJump( void ) {
 		PM_ForceLegsAnim( LEGS_JUMPB );
 		pm->ps->pm_flags |= PMF_BACKWARDS_JUMP;
 	}
+}
+
+/*
+=============
+PM_CheckJump
+=============
+*/
+static qboolean PM_CheckJump( void ) {
+	if ( !PM_CanJump() ) {
+		return qfalse;
+	}
+
+	// QL autohop: no PMF_JUMP_HELD gate here.
+	// The Pmove() outer loop forces upmove=20 when
+	// PMF_JUMP_HELD is set, allowing continuous bunny hopping.
+
+	PM_Jump();
 
 	return qtrue;
 }

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);
+	// QL pm_airSteps: allow step-ups with upward velocity.
-	down[2] -= STEPSIZE;
+	// Q3 blocked step-ups during jumps unless ground was directly below.
-	pm->trace (&trace, start_o, pm->mins, pm->maxs, down, pm->ps->clientNum, pm->tracemask);
+	// This prevented smooth stair traversal while bunny-hopping.
-	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;
-	}
 
 	VectorCopy (pm->ps->origin, down_o);
 	VectorCopy (pm->ps->velocity, down_v);
@@ -285,9 +279,15 @@ 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 ) {
+		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
 	// if the down trace can trace back to the original position directly, don't step

code/game/q_shared.h

@@ -1212,6 +1212,9 @@ typedef struct playerState_s {
 	int			pmove_framecount;	// FIXME: don't transmit over the network
 	int			jumppad_frame;
 	int			entityEventSequence;
+
+	// QL additions
+	int			lastJumpTime;		// serverTime of last jump, for 100ms cooldown
 } playerState_t;
 
 

code/qcommon/msg.c

@@ -1147,7 +1147,8 @@ netField_t	playerStateFields[] =
 { PSF(grapplePoint[1]), 0 },
 { PSF(grapplePoint[2]), 0 },
 { PSF(jumppad_ent), 10 },
-{ PSF(loopSound), 16 }
+{ PSF(loopSound), 16 },
+{ PSF(lastJumpTime), 32 }
 };
 
 /*