From 1c5c82a60945082344a186b664dbb3b9d0d1a4bd Mon Sep 17 00:00:00 2001
From: Leonardo Zide <leozide@gmail.com>
Date: Wed, 25 Dec 2019 12:25:32 -0800
Subject: [PATCH] Avoid rolling the camera when using Look At. Fixes #407.

---
 common/camera.cpp | 37 ++++++++++++++++++++++++++++++++++---
 common/camera.h   |  2 +-
 common/lc_math.h  |  8 --------
 3 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/common/camera.cpp b/common/camera.cpp
index 1480aa77..17c71744 100644
--- a/common/camera.cpp
+++ b/common/camera.cpp
@@ -957,15 +957,46 @@ void lcCamera::Roll(float Distance, lcStep Step, bool AddKey)
 	UpdatePosition(Step);
 }
 
-void lcCamera::Center(lcVector3& point, lcStep Step, bool AddKey)
+void lcCamera::Center(const lcVector3& NewCenter, lcStep Step, bool AddKey)
 {
-	lcAlign(mTargetPosition, mPosition, point);
+	const lcMatrix44 Inverse = lcMatrix44AffineInverse(mWorldView);
+	const lcVector3 Direction = -lcVector3(Inverse[2]);
+
+	float Yaw, Pitch, Roll;
+
+	if (fabsf(Direction.z) < 0.9999f)
+	{
+		Yaw = atan2f(Direction.y, Direction.x);
+		Pitch = asinf(Direction.z);
+		Roll = atan2f(Inverse[0][2], Inverse[1][2]);
+	}
+	else
+	{
+		Yaw = 0.0f;
+		Pitch = asinf(Direction.z);
+		Roll = atan2f(Inverse[0][1], Inverse[1][1]);
+	}
+
+	mTargetPosition = NewCenter;
+
+	lcVector3 FrontVector(mPosition - mTargetPosition);
+	lcMatrix44 Rotation = lcMatrix44FromAxisAngle(FrontVector, Roll);
+
+	lcVector3 UpVector(0, 0, 1), SideVector;
+	FrontVector.Normalize();
+	if (fabsf(lcDot(UpVector, FrontVector)) > 0.99f)
+		SideVector = lcVector3(-1, 0, 0);
+	else
+		SideVector = lcCross(FrontVector, UpVector);
+	UpVector = lcCross(SideVector, FrontVector);
+	UpVector.Normalize();
+	mUpVector = lcMul30(UpVector, Rotation);
 
 	if (IsSimple())
 		AddKey = false;
 
-	ChangeKey(mPositionKeys, mPosition, Step, AddKey);
 	ChangeKey(mTargetPositionKeys, mTargetPosition, Step, AddKey);
+	ChangeKey(mUpVectorKeys, mUpVector, Step, AddKey);
 
 	UpdatePosition(Step);
 }
diff --git a/common/camera.h b/common/camera.h
index fc1a988f..a3a9ae17 100644
--- a/common/camera.h
+++ b/common/camera.h
@@ -281,7 +281,7 @@ public:
 	void Pan(const lcVector3& Distance, lcStep Step, bool AddKey);
 	void Orbit(float DistanceX, float DistanceY, const lcVector3& CenterPosition, lcStep Step, bool AddKey);
 	void Roll(float Distance, lcStep Step, bool AddKey);
-	void Center(lcVector3& point, lcStep Step, bool AddKey);
+	void Center(const lcVector3& NewCenter, lcStep Step, bool AddKey);
 	void MoveSelected(lcStep Step, bool AddKey, const lcVector3& Distance);
 	void MoveRelative(const lcVector3& Distance, lcStep Step, bool AddKey);
 	void SetViewpoint(lcViewpoint Viewpoint);
diff --git a/common/lc_math.h b/common/lc_math.h
index 8b511bc3..c83fca5b 100644
--- a/common/lc_math.h
+++ b/common/lc_math.h
@@ -482,14 +482,6 @@ inline lcVector3 lcNormalize(const lcVector3& a)
 	return Ret;
 }
 
-inline void lcAlign(lcVector3& t, const lcVector3& a, const lcVector3& b)
-{
-	lcVector3 Vector(b - a);
-	Vector.Normalize();
-	Vector *=  (t - a).Length();
-	t = a + Vector;
-}
-
 inline float lcDot(const lcVector3& a, const lcVector3& b)
 {
 	return a.x * b.x + a.y * b.y + a.z * b.z;