Make thruster visual more consistent

Author: sam52796

src/scenegraph/Thruster.cpp

@@ -143,10 +143,13 @@ namespace SceneGraph {
 		m_tMat->diffuse = m_glowMat->diffuse = currentColor;
 
 		//directional fade
-		vector3f cdir = vector3f(trans * -dir).Normalized();
-		vector3f vdir = vector3f(trans[2], trans[6], -trans[10]).Normalized();
+		// In view space, camera is at origin, so view direction is from thruster position to origin.
+		vector3f flameDir = trans.ApplyRotationOnly(vector3f(0.f, 0.f, 1.f)).Normalized();
+		vector3f thrusterPos = trans.GetTranslate();
+		vector3f vdir = (thrusterPos.LengthSqr() > 1e-8f) ? (-thrusterPos).Normalized() : flameDir;
+		float facing = Clamp(std::abs(vdir.Dot(flameDir)), 0.f, 1.f);
 		// XXX check this for transition to new colors.
-		m_glowMat->diffuse.a = Easing::Circ::EaseIn(Clamp(vdir.Dot(cdir), 0.f, 1.f), 0.f, 1.f, 1.f) * 255;
+		m_glowMat->diffuse.a = Easing::Circ::EaseIn(facing, 0.f, 1.f, 1.f) * 255;
 		m_tMat->diffuse.a = 255 - m_glowMat->diffuse.a;
 
 		Graphics::Renderer *r = GetRenderer();