[TF2] fix explosions being blocked by small protrusions from the ground's geometry (splash bug/stair bug)

src/game/shared/tf/tf_gamerules.cpp

@@ -5752,6 +5752,8 @@ void CTFRadiusDamageInfo::CalculateFalloff( void )
 //-----------------------------------------------------------------------------
 // Purpose: Attempt to apply the radius damage to the specified entity
 //-----------------------------------------------------------------------------
+ConVar tf_radiusdamage_los_simple( "tf_radiusdamage_los_simple", "0", FCVAR_NONE, "Use simpler line-of-sight checks for radius damage" );
+ConVar tf_radiusdamage_los_debug( "tf_radiusdamage_los_debug", "0", FCVAR_CHEAT );
 int CTFRadiusDamageInfo::ApplyToEntity( CBaseEntity *pEntity )
 {
 	if ( pEntity == pEntityIgnore || pEntity->m_takedamage == DAMAGE_NO )
@@ -5780,11 +5782,77 @@ int CTFRadiusDamageInfo::ApplyToEntity( CBaseEntity *pEntity )
 		UTIL_TraceLine( vecSrc, vecSpot, MASK_RADIUS_DAMAGE, &filterSelf, &tr );
 	}
 
+	bool bDebugLoS = tf_radiusdamage_los_debug.GetBool() && ( pEntity->IsPlayer() || tf_radiusdamage_los_debug.GetInt() == 2 );
+
+	if ( bDebugLoS )
+	{
+		NDebugOverlay::Line( tr.startpos, tr.endpos, 255, 0, 0, true, 3 );
+		NDebugOverlay::Line( tr.endpos, vecSpot, 96, 0, 0, true, 3 );
+	}
+
 	// If we don't trace the whole way to the target, and we didn't hit the target entity, we're blocked
 	if ( tr.fraction != 1.f && tr.m_pEnt != pEntity )
 	{
-		// Don't let projectiles block damage
-		return 0;
+		if ( tf_radiusdamage_los_simple.GetBool() )
+			return 0;
+
+		if ( pEntity == dmgInfo->GetAttacker() )
+			return 0;
+
+		if ( tr.startsolid )
+			return 0;
+
+		// explosions can get blocked by bits of ground geometry such as stair steps, which is frustrating for players
+		// so when the initial LoS-check fails, let's try to find a raised position to perform a second LoS-check from 
+
+		float flStepHeight = 18.f;
+
+		Vector vecStartPos = tr.endpos;
+		Vector vecTarget = vecStartPos;
+		vecTarget.z -= flStepHeight;
+
+		// trace down to find walkable ground
+		trace_t	trStep;
+		UTIL_TraceLine( vecStartPos, vecTarget, MASK_RADIUS_DAMAGE, &filter, &trStep );
+
+		if ( bDebugLoS )
+		{
+			NDebugOverlay::Line( trStep.startpos, trStep.endpos, 0, 128, 255, true, 3 );
+		}
+
+		if ( trStep.fraction == 1.f || trStep.plane.normal.z < 0.7 )
+			// don't splash if we can't find walkable ground
+			// this stops Soldiers from splashing high-ground targets by shooting at the edge of the ledge from below
+			return 0;
+
+		if ( trStep.endpos.z > vecSpot.z )
+			// this is higher than the target's position
+			return 0;
+
+		vecStartPos = trStep.endpos;
+		vecTarget = vecStartPos;
+		vecTarget.z += flStepHeight;
+
+		// trace up from the floor to simulate step up
+		UTIL_TraceLine( vecStartPos, vecTarget, MASK_RADIUS_DAMAGE, &filter, &trStep );
+
+		if ( bDebugLoS )
+		{
+			NDebugOverlay::Line( trStep.startpos, trStep.endpos, 0, 255, 255, true, 3 );
+		}
+
+		// check if explosion can see target from this raised position
+		UTIL_TraceLine( trStep.endpos, vecSpot, MASK_RADIUS_DAMAGE, &filter, &trStep );
+
+		if ( bDebugLoS )
+		{
+			NDebugOverlay::Line( trStep.startpos, trStep.endpos, 0, 255, 0, true, 3 );
+			NDebugOverlay::Line( trStep.endpos, vecSpot, 0, 96, 0, true, 3 );
+		}
+
+		if ( trStep.startsolid || trStep.fraction != 1.f && trStep.m_pEnt != pEntity )
+			// target is still blocked
+			return 0;
 	}
 
 	// Adjust the damage - apply falloff.