From fb1f93b825f679cf1e3d18e47960e8fee057a2e7 Mon Sep 17 00:00:00 2001
From: = <=>
Date: Wed, 17 Mar 2021 15:41:58 -0400
Subject: [PATCH] add constructEllipseAE

---
 src/main.cpp         | 10 +++-------
 src/orbits.cpp       | 19 +++++++++++++++++--
 src/orbits.h         | 11 ++++++++++-
 tests/orbit_test.cpp |  4 +---
 4 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 9625c15..be31a17 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -70,10 +70,8 @@ initOrbit()
 
 	double a = 26564.5; // kilometers
 	double e = 0.7411;
-	double b = a * sqrt(1 - pow(e, 2.0));
-	orbit.ep = constructEllipse(a, b);
+	orbit.ep = constructEllipseAE(a, e);
 	orbit.mu = 398601.68; // NOTE: earth's gravitational parameter in km^3/s^2
-
 	return orbit;
 }
 
@@ -94,9 +92,7 @@ doFrameCallbackPre(render_state* rs)
 		rs->running = false;
 
 	// update orbital elements/ellipse_3d
-	// TODO: could really use another ellipse constructor that uses a and e
-	g_orbit.ep = constructEllipseAB(g_orbit.ep.a,
-		g_orbit.ep.a * sqrt(1 - pow(g_orbit.ep.e, 2.0)));
+	g_orbit.ep = constructEllipseAE(g_orbit.ep.a, g_orbit.ep.e);
 	entity& ellipse_entity = rs->render_groups[0].entities[0];
 
 	// TODO: fix this
@@ -159,7 +155,7 @@ main()
 	);
 
 	g_orbit = initOrbit();
-	ellipse_parameters ep = constructEllipse(g_orbit.ep.a, g_orbit.ep.b);
+	ellipse_parameters ep = constructEllipseAB(g_orbit.ep.a, g_orbit.ep.b);
 
 	// TODO: (renderer) this needs to be more convenient
 	shader_wrapper sw = { SIMPLE_SHADER, nullptr, rs->simple_shader };
diff --git a/src/orbits.cpp b/src/orbits.cpp
index 1fbf802..dc05ee0 100644
--- a/src/orbits.cpp
+++ b/src/orbits.cpp
@@ -3,7 +3,7 @@
 
 
 ellipse_parameters
-constructEllipse(double a, double b)
+constructEllipseAB(double a, double b)
 {
 	assert(a > 0 && b > 0 && a >= b);
 	ellipse_parameters ep = { a, b };
@@ -12,7 +12,22 @@ constructEllipse(double a, double b)
 	ep.p = ep.a * (1 - pow(ep.e, 2));
 	ep.f1.x = -1 * ep.c;
 	ep.f2.x = ep.c;
-	return ep; }
+	return ep;
+}
+
+ellipse_parameters
+constructEllipseAE(double a, double e)
+{
+	assert(e >= 0 && e < 1);
+	double b = a * sqrt(1 - pow(e, 2.0));
+	return constructEllipseAB(a, b);
+}
+
+bool
+validateEllipse(ellipse_parameters)
+{
+	return false;
+}
 
 ellipse_3d
 constructEllipse3D(ellipse_parameters ep, uint vert_count)
diff --git a/src/orbits.h b/src/orbits.h
index 29c635b..c185d52 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -37,13 +37,22 @@ struct ellipse_3d
 
 
 ellipse_parameters
-constructEllipse(double a, double b);
+constructEllipseAB(double a, double b);
+
+ellipse_parameters
+constructEllipseAE(double a, double e);
+
+bool
+validateEllipse(ellipse_parameters);
 
 // NOTE: create vertices for a 3d ellipse
 // NOTE: all vertices are in the x/y plane with z = 0
 ellipse_3d
 constructEllipse3D(ellipse_parameters ep, uint vert_count);
 
+bool
+ellipsesEqual(ellipse_parameters e1, ellipse_parameters e2);
+
 /* NOTE: how-to propagate orbit position given initial true anomaly, semimajor
  *	axis, mean motion, and eccentricity: ref) section 4.4, Kepler's Problem,
  * 	"Space Flight Dynamics" by Craig A. Kluever
diff --git a/tests/orbit_test.cpp b/tests/orbit_test.cpp
index 3d8eacc..7380b37 100644
--- a/tests/orbit_test.cpp
+++ b/tests/orbit_test.cpp
@@ -20,11 +20,9 @@ TEST_CASE("orbit construction", "[orbits]")
 TEST_CASE("orbit propagation", "[orbits]")
 {
 	orbital_elements orbit = {};
-	// TODO: might want another contructor for ellipse_parameters
 	double a = 26564.5; // kilometers
 	double e = 0.7411;
-	double b = a * sqrt(1 - pow(e, 2.0));
-	ellipse_parameters ep = constructEllipse(a, b);
+	ellipse_parameters ep = constructEllipseAE(a, e);
 	orbit.ep = ep;
 	double initial_anom = 260 * M_PI / 180; // radians
 	unsigned int time_step = 60 * 50; // seconds