From f7a424cd0681170198a9864259f029ab34b2eb1c Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Fri, 21 May 2021 18:25:30 +0200
Subject: [PATCH] - fixed precision issues with GetClosestPointOnWall for
 orthogonal lines.

The math failed for some large wall sprites (e.g. Blood E2M4, sprite #181), and in orthogonal cases it is better anyway to perform direct checks of the coordinates
---
 source/core/rendering/scene/hw_walls.cpp | 32 +++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/source/core/rendering/scene/hw_walls.cpp b/source/core/rendering/scene/hw_walls.cpp
index 9b50959ea..33bb3c09e 100644
--- a/source/core/rendering/scene/hw_walls.cpp
+++ b/source/core/rendering/scene/hw_walls.cpp
@@ -46,17 +46,43 @@
 //
 //==========================================================================
 
-static int GetClosestPointOnWall(vec2_t const* const pos, walltype* wal, vec2_t* const n)
+static int GetClosestPointOnWall(spritetype* spr, walltype* wal, vec2_t* const n)
 {
 	auto w = wal->pos;
 	auto d = wall[wal->point2].pos - w;
-	int64_t i = d.x * ((int64_t)pos->x - w.x) + d.y * ((int64_t)pos->y - w.y);
+	auto pos = spr->pos;
 
+	// avoid the math below for orthogonal walls. Here we allow only sprites that exactly match the line's coordinate and orientation
 	if (d.x == 0 && d.y == 0)
 	{
+		// line has no length.
 		// In Blood's E1M1 this gets triggered for wall 522.
 		return 1;
 	}
+	else if (d.x == 0)
+	{
+		// line is vertical.
+		if (pos.x == w.x && (spr->ang & 0x3ff) == 0)
+		{
+			*n = pos.vec2;
+			return 0;
+		}
+		return 1;
+	}
+	else if (d.y == 0)
+	{
+		// line is horizontal.
+		if (pos.y == w.y && (spr->ang & 0x3ff) == 0x200)
+		{
+			*n = pos.vec2;
+			return 0;
+		}
+		return 1;
+	}
+
+
+	int64_t i = d.x * ((int64_t)pos.x - w.x) + d.y * ((int64_t)pos.y - w.y);
+
 
 	if (i < 0)
 		return 1;
@@ -91,7 +117,7 @@ static int IsOnWall(spritetype* tspr, int height)
 	{
 		auto wal = &wall[i];
 		if ((wal->nextsector == -1 || ((sector[wal->nextsector].ceilingz > topz) ||
-			sector[wal->nextsector].floorz < tspr->z)) && !GetClosestPointOnWall(&tspr->pos.vec2, wal, &n))
+			sector[wal->nextsector].floorz < tspr->z)) && !GetClosestPointOnWall(tspr, wal, &n))
 		{
 			int const dst = abs(tspr->x - n.x) + abs(tspr->y - n.y);