chore: extract retrieving cartesian elements

src/main.cpp

@@ -37,6 +37,7 @@
 
 #include <GL/glew.h>
 #include <GLFW/glfw3.h>
+#include <astro/stateVectorIndices.hpp>
 
 #include "gfx.hpp"
 #include "icosphere.hpp"
@@ -54,7 +55,14 @@ int main()
 
     Icosphere planet(0.2, 3, litProgram);
     Icosphere orbiter(0.07, 2, litProgram);
-    Orbit orbit(100);
+
+    std::vector<float> keplerianElements(6);
+    keplerianElements[astro::semiMajorAxisIndex] = .75;
+    keplerianElements[astro::eccentricityIndex] = .5;
+    keplerianElements[astro::inclinationIndex] = 3.142 / 2.0 + 1;
+    keplerianElements[astro::argumentOfPeriapsisIndex] = 2.0;
+    keplerianElements[astro::longitudeOfAscendingNodeIndex] = 0;
+    Orbit orbit(keplerianElements);
 
     Widget widget(orbit, unlitProgram);
 
@@ -65,8 +73,25 @@ int main()
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
         float time = glfwGetTime();
+        const float orbitalPeriod = 6.284;
 
-        glm::vec3 pos = orbit.getPosition(time);
+        const int ANIM_ORBITING = 0;
+        const int ANIM_ECCENTRICITY = 1;
+        int animation = (int)(time / orbitalPeriod) % 2 == 1;
+
+        glm::vec3 pos;
+        if (animation == ANIM_ORBITING)
+        {
+            pos = orbit.getPosition(time);
+        }
+        else if (animation == ANIM_ECCENTRICITY)
+        {
+            float e = .25 + .2 * sin(time);
+            keplerianElements[astro::eccentricityIndex] = e;
+            orbit.setElements(keplerianElements);
+
+            pos = orbit.getPosition(0);
+        }
         orbiter.setPosition(pos);
 
         // Render lit objects

src/orbit.cpp

@@ -3,18 +3,22 @@
 #include "astro/stateVectorIndices.hpp"
 #include "astro/orbitalElementConversions.hpp"
 
-Orbit::Orbit(int vertexCount) :
-    _keplerianElements(std::vector<float>(6))
+Orbit::Orbit(Vector6 keplerianElements) :
+    _keplerianElements(keplerianElements)
 {
-    _keplerianElements[astro::semiMajorAxisIndex] = .75;
-    _keplerianElements[astro::eccentricityIndex] = .5;
-    _keplerianElements[astro::inclinationIndex] = _pi / 2.0 + 1;
-    _keplerianElements[astro::argumentOfPeriapsisIndex] = 2.0;
-    _keplerianElements[astro::longitudeOfAscendingNodeIndex] = 0;
+    glGenVertexArrays(1, &_vao);
+    glGenBuffers(1, &_vbo);
 
-    for (int i = 0; i < vertexCount; i++)
+    regenerateVertices();
+}
+
+void Orbit::regenerateVertices()
+{
+    _vertices.clear();
+
+    for (int i = 0; i < _vertexCount; i++)
     {
-        float t = (float)i / (float)vertexCount * 2.0 * _pi;
+        float t = (float)i / (float)_vertexCount * 2.0 * _pi;
         glm::vec3 pos = getPosition(t);
 
         _vertices.push_back(pos.x);
@@ -22,9 +26,6 @@ Orbit::Orbit(int vertexCount) :
         _vertices.push_back(pos.z);
     }
 
-    glGenVertexArrays(1, &_vao);
-    glGenBuffers(1, &_vbo);
-
     glBindVertexArray(_vao);
 
     glBindBuffer(GL_ARRAY_BUFFER, _vbo);
@@ -38,11 +39,14 @@ Orbit::Orbit(int vertexCount) :
     glBindVertexArray(0);
 }
 
-// Interpolate a position around the orbit.
-// t is in range 0..1 and wraps.
-glm::vec3 Orbit::getPosition(const float meanAnomaly)
+void Orbit::setElements(Vector6 keplerianElements)
+{
+    _keplerianElements = keplerianElements;
+    regenerateVertices();
+}
+
+float Orbit::getEccentricAnomaly(const float meanAnomaly)
 {
-    // Get eccentric anomaly from elliptical mean anomaly
     const float eccentricity = _keplerianElements[astro::eccentricityIndex];
     float eccentricAnomaly = astro::convertEllipticalMeanAnomalyToEccentricAnomaly(
         eccentricity,
@@ -50,21 +54,36 @@ glm::vec3 Orbit::getPosition(const float meanAnomaly)
         (float)10e-3,
         100);
 
-    // Get true anomaly from eccentric anomaly
-    float trueAnomaly = astro::convertEccentricAnomalyToTrueAnomaly(
-        eccentricAnomaly,
-        eccentricity);
+    return eccentricAnomaly;
+}
 
-    std::vector<float> kepler(_keplerianElements);
-    kepler[astro::trueAnomalyIndex] = trueAnomaly;
-
-    std::vector<float> cartesian = astro::convertKeplerianToCartesianElements(kepler, 1.0);
+// Interpolate a position around the orbit.
+// t is in range 0..1 and wraps.
+glm::vec3 Orbit::getPosition(const float meanAnomaly)
+{
+    Vector6 cartesian = getCartesianCoordinates(meanAnomaly);
     return glm::vec3(
         cartesian[astro::xPositionIndex],
         cartesian[astro::yPositionIndex],
         cartesian[astro::zPositionIndex]);
 }
 
+float Orbit::getTrueAnomaly(const float meanAnomaly)
+{
+    const float eccentricAnomaly = getEccentricAnomaly(meanAnomaly);
+    const float eccentricity = _keplerianElements[astro::eccentricityIndex];
+    return astro::convertEccentricAnomalyToTrueAnomaly(
+        eccentricAnomaly,
+        eccentricity);
+}
+
+Vector6 Orbit::getCartesianCoordinates(const float meanAnomaly)
+{
+    Vector6 kepler(_keplerianElements);
+    kepler[astro::trueAnomalyIndex] = getTrueAnomaly(meanAnomaly);
+    return astro::convertKeplerianToCartesianElements(kepler, 1.0);
+}
+
 glm::vec3 Orbit::getTangent(const float meanAnomaly)
 {
     float epsilon = 0.01;

src/orbit.hpp

@@ -5,22 +5,35 @@
 
 #include "glm/glm.hpp"
 
+typedef std::vector<float> Vector6;
+
 class Orbit
 {
 public:
-    Orbit(int vertexCount);
+    Orbit(Vector6 keplerianElements);
     void render();
 
+    // TODO: meanAnomaly in all these arguments actually means eccentricMeanAnomaly,
+    // will have to change that when adding non-ellipctical orbits - don't get confused!
     glm::vec3 getPosition(const float meanAnomaly);
     glm::vec3 getTangent(const float meanAnomaly);
 
+    void setElements(Vector6 keplerianElements);
+
     ~Orbit(); 
 private:
     const float _pi = 3.14159265359;
+    const int _vertexCount = 100;
 
     GLuint _vbo;
     GLuint _vao;
 
     std::vector<float> _vertices;
-    std::vector<float> _keplerianElements;
+    Vector6 _keplerianElements;
+
+    void regenerateVertices();
+
+    float getEccentricAnomaly(const float meanAnomaly);
+    float getTrueAnomaly(const float meanAnomaly);
+    Vector6 getCartesianCoordinates(const float meanAnomaly);
 };