From faf98684a3bec496f0193bc77bc811a216dc6501 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Thu, 27 Oct 2022 09:29:08 +0200
Subject: [PATCH] - rewrote cliptrace.

Completely new implementation reusing nothing of the original.

# Conflicts:
#	source/build/src/clip.cpp
#	source/core/gamefuncs.cpp
#	source/core/gamefuncs.h
---
 source/core/gamefuncs.cpp | 60 +++++++++++++++++++++++++++++++++++++++
 source/core/gamefuncs.h   |  3 +-
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/source/core/gamefuncs.cpp b/source/core/gamefuncs.cpp
index 3a909b508..ca2823377 100644
--- a/source/core/gamefuncs.cpp
+++ b/source/core/gamefuncs.cpp
@@ -1606,6 +1606,66 @@ void collectClipObjects(MoveClipper& clip, int spritemask)
 //
 //==========================================================================
 
+int cliptrace(MoveClipper& clip, const DVector2& fpos, DVector2& fgoal)
+{
+	int32_t hitwall = -1;
+
+	DVector2 move = fgoal - fpos;
+	double bestfactor = 1.;
+	ClipObject* bestclip = nullptr;
+
+	for (auto& clipo : clip.clipobjects)
+	{
+		auto p1 = clipo.line.start;
+		auto delta = clipo.line.end - p1;
+
+		double factor = InterceptLineSegments(fpos.X, fpos.Y, move.X, move.Y, p1.X, p1.Y, delta.X, delta.Y);
+		if (factor > 0 && factor < bestfactor)
+		{
+			bestfactor = factor;
+			bestclip = &clipo;
+		}
+	}
+
+	DVector2 hit = fpos;
+	if (bestfactor < 1)
+	{
+		// account for math imprecisions and ensure that the resulting hit point is always at the front side of the line.
+
+		auto p1 = bestclip->line.start;
+		auto delta = bestclip->line.end - p1;
+		double len = move.Length();
+		move /= len;
+		bestfactor *= len;
+
+		for (int i = 0; i < 256; i++)
+		{
+			hit = fpos + move * bestfactor;
+			// Do this on the original Build coordinate grid to avoid problems with expectations on the game side.
+			hit.X = xs_CRoundToInt(hit.X * worldtoint) * inttoworld;
+			hit.Y = xs_CRoundToInt(hit.Y * worldtoint) * inttoworld;
+			if (PointOnLineSide(hit.X, hit.Y, p1.X, p1.Y, delta.X, delta.Y) < 0)
+			{
+				hitwall = bestclip - clip.clipobjects.Data();
+				break;
+			}
+			bestfactor -= maptoworld * 0.5;
+			if (bestfactor <= 0) break;
+		}
+	}
+	if (hitwall != -1)
+	{
+		fgoal = hit;
+	}
+	return hitwall;
+}
+
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
 sectortype* FindSectorInSearchList(const DVector3& pos, BFSSectorSearch& search)
 {
 	search.Rewind();
diff --git a/source/core/gamefuncs.h b/source/core/gamefuncs.h
index a37023108..8a6ee066d 100644
--- a/source/core/gamefuncs.h
+++ b/source/core/gamefuncs.h
@@ -319,7 +319,8 @@ sectortype* FindSectorInSearchList(const DVector3& pos, BFSSectorSearch& search)
 void PushAway(MoveClipper &clip, DVector2& pos, sectortype* sect);
 void keepaway(MoveClipper& clip, DVector2& pos, ClipObject& clipo);
 
-int FindBestSector(const DVector3& pos);
+
+
 
 tspritetype* renderAddTsprite(tspriteArray& tsprites, DCoreActor* actor);