From 29d9bafb9e405fe6df8db2abc273c06def5356dd Mon Sep 17 00:00:00 2001
From: James R <justsomejames2@gmail.com>
Date: Sun, 14 Feb 2021 23:04:17 -0800
Subject: [PATCH] Snap finish line waypoints to the nearest point of the finish
 line

Finish line waypoints must be exactly on the finish line to avoid erroneous
finish line distance from crossing the waypoint before/after the line. This
is only a problem in circuit maps and on laps before the last, due to the
multiplied circuit length.
---
 src/p_mobj.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/p_mobj.c b/src/p_mobj.c
index 2bc6c620f..ac48b953d 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -11325,6 +11325,39 @@ static boolean P_SetupBooster(mapthing_t* mthing, mobj_t* mobj, boolean strong)
 	return true;
 }
 
+static fixed_t dist2vert(const vertex_t *v, const mobj_t *o)
+{
+	return abs(FixedHypot(v->x - o->x, v->y - o->y));
+}
+
+static void P_SnapToFinishLine(mobj_t *mobj)
+{
+	const sector_t *sector = mobj->subsector->sector;
+	size_t i;
+	fixed_t d;
+	fixed_t nearest = INT32_MAX;
+	line_t *nearest_line = NULL;
+	for (i = 0; i < sector->linecount; ++i)
+	{
+		if (
+				sector->lines[i]->special == 2001 && // case 2001: Finish Line
+				(
+					(d = dist2vert(sector->lines[i]->v1, mobj)) < nearest ||
+					(d = dist2vert(sector->lines[i]->v2, mobj)) < nearest
+				)
+		){
+			nearest = d;
+			nearest_line = sector->lines[i];
+		}
+	}
+	if (nearest < INT32_MAX)
+	{
+		P_UnsetThingPosition(mobj);
+		P_ClosestPointOnLine(mobj->x, mobj->y, nearest_line, (vertex_t *)&mobj->x);
+		P_SetThingPosition(mobj);
+	}
+}
+
 static boolean P_SetupSpawnedMapThing(mapthing_t *mthing, mobj_t *mobj, boolean *doangle)
 {
 	boolean override = LUAh_MapThingSpawn(mobj, mthing);
@@ -11708,7 +11741,8 @@ static boolean P_SetupSpawnedMapThing(mapthing_t *mthing, mobj_t *mobj, boolean
 		}
 		if (mthing->args[2] == 1)
 		{
-			mobj->extravalue2 = 1; // args[1] of 1 means the waypoint is at the finish line
+			mobj->extravalue2 = 1; // args[2] of 1 means the waypoint is at the finish line
+			P_SnapToFinishLine(mobj);
 		}
 		else
 		{