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;

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;
 }
 
@@ -392,7 +400,23 @@ void PM_Jump( void ) {
 	pm->ps->pm_flags |= PMF_JUMP_HELD;
 
 	pm->ps->groundEntityNum = ENTITYNUM_NONE;
-	pm->ps->velocity[2] = JUMP_VELOCITY;
+
+	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 );
 

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);
@@ -285,8 +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