From 2624ccd8ba673ba79a99d24357458d763ac1e4c3 Mon Sep 17 00:00:00 2001
From: Tiger Wang <ziwei.tiger@outlook.com>
Date: Tue, 14 Jul 2020 17:55:25 +0100
Subject: Gracefully handle rounding issues

---
 src/BoundingBox.cpp     | 16 ++++++++++------
 src/Entities/Entity.cpp | 25 +++++++++++++++++--------
 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/src/BoundingBox.cpp b/src/BoundingBox.cpp
index 1356e165c..e60be3476 100644
--- a/src/BoundingBox.cpp
+++ b/src/BoundingBox.cpp
@@ -213,41 +213,45 @@ bool cBoundingBox::CalcLineIntersection(Vector3d a_Min, Vector3d a_Max, Vector3d
 		return true;
 	}
 
+	// Correction for floating point imprecision when calculating
+	// the coefficient to intersect a plane by slightly increasing it
+	static const auto Correction = 1.000001;
+
 	eBlockFace Face = BLOCK_FACE_NONE;
 	double Coeff = Vector3d::NO_INTERSECTION;
 
 	// Check each individual bbox face for intersection with the line, remember the one with the lowest coeff
-	double c = a_Line1.LineCoeffToXYPlane(a_Line2, a_Min.z);
+	double c = a_Line1.LineCoeffToXYPlane(a_Line2, a_Min.z) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.z > a_Line2.z) ? BLOCK_FACE_ZP : BLOCK_FACE_ZM;
 		Coeff = c;
 	}
-	c = a_Line1.LineCoeffToXYPlane(a_Line2, a_Max.z);
+	c = a_Line1.LineCoeffToXYPlane(a_Line2, a_Max.z) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.z > a_Line2.z) ? BLOCK_FACE_ZP : BLOCK_FACE_ZM;
 		Coeff = c;
 	}
-	c = a_Line1.LineCoeffToXZPlane(a_Line2, a_Min.y);
+	c = a_Line1.LineCoeffToXZPlane(a_Line2, a_Min.y) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.y > a_Line2.y) ? BLOCK_FACE_YP : BLOCK_FACE_YM;
 		Coeff = c;
 	}
-	c = a_Line1.LineCoeffToXZPlane(a_Line2, a_Max.y);
+	c = a_Line1.LineCoeffToXZPlane(a_Line2, a_Max.y) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.y > a_Line2.y) ? BLOCK_FACE_YP : BLOCK_FACE_YM;
 		Coeff = c;
 	}
-	c = a_Line1.LineCoeffToYZPlane(a_Line2, a_Min.x);
+	c = a_Line1.LineCoeffToYZPlane(a_Line2, a_Min.x) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.x > a_Line2.x) ? BLOCK_FACE_XP : BLOCK_FACE_XM;
 		Coeff = c;
 	}
-	c = a_Line1.LineCoeffToYZPlane(a_Line2, a_Max.x);
+	c = a_Line1.LineCoeffToYZPlane(a_Line2, a_Max.x) * Correction;
 	if ((c >= 0) && (c < Coeff) && IsInside(a_Min, a_Max, a_Line1 + (a_Line2 - a_Line1) * c))
 	{
 		Face = (a_Line1.x > a_Line2.x) ? BLOCK_FACE_XP : BLOCK_FACE_XM;
diff --git a/src/Entities/Entity.cpp b/src/Entities/Entity.cpp
index 37ef925cf..1f270cff0 100644
--- a/src/Entities/Entity.cpp
+++ b/src/Entities/Entity.cpp
@@ -1067,9 +1067,15 @@ void cEntity::HandlePhysics(std::chrono::milliseconds a_Dt, cChunk & a_Chunk)
 
 			// TODO: checks too much, very inefficient
 			for (int i = bstart.x; i <= bend.x; i++)
-			for (int j = bstart.y; j <= bend.y; j++)
-			for (int k = bstart.z; k <= bend.z; k++)
-				Checks.emplace(Vector3i(i, j, k));
+			{
+				for (int j = bstart.y; j <= bend.y; j++)
+				{
+					for (int k = bstart.z; k <= bend.z; k++)
+					{
+						Checks.emplace(Vector3i(i, j, k));
+					}
+				}
+			}
 
 			return Checks;
 		}
@@ -1146,15 +1152,18 @@ void cEntity::HandlePhysics(std::chrono::milliseconds a_Dt, cChunk & a_Chunk)
 			eBlockFace Face;  // Face hit
 			cBoundingBox bb(a_BlockPos, a_BlockPos + Vector3i(1, 1, 1));  // Bounding box of the block hit
 
+			// First calculate line intersection
 			if (!bb.CalcLineIntersection(m_Start, m_End, LineCoeff, Face))
 			{
-				// Math rounding errors have caused the calculation to miss the block completely, assume immediate hit
-				LineCoeff = 0;
+				// Maths rounding errors have caused the calculation to miss the block completely
+				m_HitCoords = m_End;
+				m_HitBlockFace = BLOCK_FACE_NONE;
+				return true;
 			}
 
-			m_HitCoords = m_Start + (m_End - m_Start) * LineCoeff;  // Point where projectile goes into the hit block
-
-			TestBoundingBoxCollisionWithEnvironment(m_HitCoords);
+			// Check bbox collision, setting final values
+			// Line tracer hit position is used as a starting point:
+			TestBoundingBoxCollisionWithEnvironment(m_Start + (m_End - m_Start) * LineCoeff);
 
 			return m_HitBlockFace != BLOCK_FACE_NONE;
 		}
-- 
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