Satellites: Avoid bad orbit lines (Fix #3934)

- Don't parallelize when orbits are needed
- Not a perfect solution, but it takes deeper
  insight into the plugin code to really solve the issue

plugins/Satellites/src/Satellite.cpp

@@ -852,7 +852,8 @@ void Satellite::update(const StelCore *core, const double JD)
 		phaseAngle = std::acos(-1.0*(std::sin(decSun)*std::sin(decSat) + std::cos(decSun)*std::cos(decSat)*std::cos(raSun - raSat)));
 
 		// Compute orbit points to draw orbit line.
-		if (orbitDisplayed) computeOrbitPoints();
+		// We suppress computing so that no lines are computed in parallel as long as this uses static variables.
+		if (orbitLinesFlag && orbitDisplayed) computeOrbitPoints();
 	}
 }
 

plugins/Satellites/src/Satellites.cpp

@@ -2840,11 +2840,25 @@ void Satellites::update(double deltaTime)
 			sat->update(core, JD);
 	}
 #else
-	const auto updateSat = [this, JD](QSharedPointer<Satellite>& sat){
-		if (sat->initialized && sat->displayed)
-			sat->update(core, JD);
-	};
-	QtConcurrent::blockingMap(QThreadPool::globalInstance(), satellites, updateSat);
+	// TODO: sat->update is an obvious candidate for parallelisation and without orbits, it indeed helps a lot.
+	// Unfortunately, the call to Satellite::computeOrbitPoints(); uses static variables, which messes up the orbit lines.
+	// We can compute satellites in parallel, but only if orbits are suppressed, until this is fixed.
+	if (getFlagOrbitLines())
+	{
+		for (const auto& sat : std::as_const(satellites))
+		{
+			if (sat->initialized && sat->displayed)
+				sat->update(core, JD);
+		}
+	}
+	else
+	{
+		const auto updateSat = [this, JD](QSharedPointer<Satellite>& sat){
+			if (sat->initialized && sat->displayed)
+				sat->update(core, JD);
+		};
+		QtConcurrent::blockingMap(QThreadPool::globalInstance(), satellites, updateSat);
+	}
 #endif
 }