feat: render nested orbits

lib/skein/include/skein/particlemap.h

@@ -14,6 +14,7 @@ class ParticleMap
         // providing these as two methods keeps things unambiguous - manipulating particles
         // is just done for setup
         const Particle& getParticle(const std::string& id) const;
+        const Particle& getParent(const std::string& id) const;
         glm::dvec3 getParticlePosition(const std::string& id, double time) const;
         const Orbit& getOrbit(const std::string& id) const;
 

lib/skein/src/particlemap.cpp

@@ -6,6 +6,12 @@ const Particle& ParticleMap::getParticle(const std::string& id) const
     return _particles.at(id);
 }
 
+const Particle& ParticleMap::getParent(const std::string& childId) const
+{
+    const std::string parentId = _relationships.at(childId);
+    return _particles.at(parentId);
+}
+
 const Orbit& ParticleMap::getOrbit(const std::string& id) const
 {
     return _orbits.at(id);
@@ -16,13 +22,31 @@ glm::dvec3 ParticleMap::getParticlePosition(const std::string& id, double time)
     if (_orbits.find(id) == _orbits.end())
         return {0,0,0};
 
-    const std::string& parentId = _relationships.at(id);
-    const Particle& parent = _particles.at(parentId);
-    const double gravitationalParameter = parent.getGravitationalParameter();
+    const Particle* particle = &(_particles.at(id));
+    glm::dvec3 pos(0,0,0);
 
-    // TODO: actually nest stuff so position is determined from all parents
-    const Orbit& orbit = _orbits.at(id);
-    return orbit.getPosition(gravitationalParameter, time);
+    do
+    {
+        const std::string& id = particle->getId();
+        const std::string& parentId = _relationships.at(id);
+        const Particle& parent = _particles.at(parentId);
+        const double gravitationalParameter = parent.getGravitationalParameter();
+        const Orbit& orbit = _orbits.at(id);
+
+        pos += orbit.getPosition(gravitationalParameter, time);
+
+        auto it = _relationships.find(parentId);
+        if (it != _relationships.end())
+        {
+            particle = &parent;
+        }
+        else
+        {
+            particle = nullptr;
+        }
+    } while (particle != nullptr);
+
+    return pos;
 }
 
 void ParticleMap::setParticle(const Particle& particle)

src/main.cpp

@@ -66,24 +66,35 @@ int main()
     GLuint unlitProgram = compileShaderProgram("./frag_unlit.glsl");
 
     // set parameters of moon's orbit around earth
-    Orbit orbit;
-    double semiMajorAxis =  3.84748e8;
-    orbit.setSemiMajorAxis(semiMajorAxis);      // metres
-    orbit.setEccentricity(0.055);
-    orbit.setInclination(glm::radians(5.15));   // radians
-    orbit.setArgumentOfPeriapsis(318.15);       // in the case of the moon these last two values are
-    orbit.setLongitudeOfAscendingNode(60.0);    // pretty much constantly changing so use whatever
+    Orbit moonOrbit;
+    double moonOrbitSemiMajorAxis =  3.84748e8;
+    moonOrbit.setSemiMajorAxis(moonOrbitSemiMajorAxis); // metres
+    moonOrbit.setEccentricity(0.055);
+    moonOrbit.setInclination(glm::radians(5.15));       // radians
+    moonOrbit.setArgumentOfPeriapsis(318.15);           // in the case of the moon these last two values are
+    moonOrbit.setLongitudeOfAscendingNode(60.0);        // pretty much constantly changing so use whatever
+
+    // set parameters of satellite orbit around moon
+    Orbit stationOrbit;
+    stationOrbit.setSemiMajorAxis(5e7);
+    stationOrbit.setEccentricity(0.6);
+    stationOrbit.setInclination(glm::radians(89.0));
+    stationOrbit.setArgumentOfPeriapsis(43.2);
+    stationOrbit.setLongitudeOfAscendingNode(239.7);
 
-    // TODO: add something in a nice eccentric orbit around the moon
-    // make the earth-moon system
     ParticleMap map;
     map.setParticle({"earth", 5.9e24});
     map.setParticle({"moon", 7.3e22});
-    map.setRelationship("earth", "moon", orbit);
-    float scale = semiMajorAxis * 1.1;
-    ParticleVisualizer earthVis(map, "earth", 0.2, litProgram, unlitProgram, scale);
-    ParticleVisualizer moonVis(map, "moon", 0.1, litProgram, unlitProgram, scale);
-    OrbitVisualizer orbitVis(orbit, unlitProgram, scale);
+    map.setParticle({"station", 1e6});
+    map.setRelationship("earth", "moon", moonOrbit);
+    map.setRelationship("moon", "station", stationOrbit);
+
+    float scale = moonOrbitSemiMajorAxis * 1.1;
+    ParticleVisualizer earthVis(map, "earth", 0.1, litProgram, unlitProgram, scale);
+    ParticleVisualizer moonVis(map, "moon", 0.02, litProgram, unlitProgram, scale);
+    ParticleVisualizer stationVis(map, "station", 0.01, litProgram, unlitProgram, scale);
+    OrbitVisualizer moonOrbitVis(map, "moon", unlitProgram, scale);
+    OrbitVisualizer stationOrbitVis(map, "station", unlitProgram, scale);
 
     // register input
     glfwSetKeyCallback(window, keyCallback);
@@ -125,7 +136,7 @@ int main()
         else
         {
             double e = .25 + .2 * sin(getTime());
-            orbit.setEccentricity(e);
+            moonOrbit.setEccentricity(e);
         }
 
         // rendering
@@ -134,7 +145,9 @@ int main()
 
         earthVis.render(time);
         moonVis.render(time);
-        orbitVis.render(time);
+        stationVis.render(time);
+        moonOrbitVis.render(time);
+        stationOrbitVis.render(time);
 
         glfwSwapBuffers(window);
     }

src/orbitvisualizer.cpp

@@ -1,8 +1,8 @@
 #include "orbitvisualizer.hpp"
 #include "gfx.hpp"
 
-OrbitVisualizer::OrbitVisualizer(const Orbit& orbit, const GLuint shaderProgram, float scale)
-    : _orbit(orbit), _shaderProgram(shaderProgram), _scale(scale)
+OrbitVisualizer::OrbitVisualizer(const ParticleMap& map, const std::string& particleId, const GLuint shaderProgram, float scale)
+    : _map(map), _particleId(particleId), _shaderProgram(shaderProgram), _scale(scale)
 {
     glGenVertexArrays(1, &_vao);
     glGenBuffers(1, &_vbo);
@@ -10,7 +10,11 @@ OrbitVisualizer::OrbitVisualizer(const Orbit& orbit, const GLuint shaderProgram,
 
 void OrbitVisualizer::render(const float time)
 {
-    regenerateVertices();
+    // Orbit needs to be drawn relative to its parent
+    const Particle& parent = _map.getParent(_particleId);
+    const glm::vec3 parentPos = _map.getParticlePosition(parent.getId(), time);
+
+    regenerateVertices(parentPos);
 
     glUseProgram(_shaderProgram);
     updateModelViewProjectionMatrix(_shaderProgram, time);
@@ -21,17 +25,19 @@ void OrbitVisualizer::render(const float time)
     glDrawArrays(GL_LINE_LOOP, 0, _vertices.size() / 3);
 }
 
-void OrbitVisualizer::regenerateVertices()
+void OrbitVisualizer::regenerateVertices(const glm::vec3& basePos)
 {
-    _vertices.clear();
+    const Orbit& orbit = _map.getOrbit(_particleId);
 
+    _vertices.clear();
     for (int i = 0; i < _vertexCount; i++)
     {
         // TODO: this method of getting ellipse vertices is a huge hack. it would be
         // better to actually create a first-class ellipse object and use that to generate
         // a nice continuous mesh, instead of using orbital positions. 
         float t = (float)i / (float)_vertexCount * 2.0 * _pi;
-        glm::vec3 pos = _orbit.getPositionFromMeanAnomaly(t);
+        glm::vec3 pos = orbit.getPositionFromMeanAnomaly(t);
+        pos += basePos;
 
         // Vertices come out of the library with X and Y being in the 'flat' plane. Re-order them
         // here such that Z is up.

src/orbitvisualizer.hpp

@@ -2,12 +2,12 @@
 
 #include <GL/glew.h>
 #include <vector>
-#include <skein/orbit.h>
+#include <skein/particlemap.h>
 
 class OrbitVisualizer
 {
     public:
-        OrbitVisualizer(const Orbit& orbit, const GLuint shaderProgram, float scale);
+        OrbitVisualizer(const ParticleMap& map, const std::string& particleId, const GLuint shaderProgram, float scale);
         ~OrbitVisualizer();
 
         void render(const float time);
@@ -17,12 +17,13 @@ class OrbitVisualizer
 
         const int _vertexCount = 100;
         const GLuint _shaderProgram;
-        const Orbit& _orbit;
+        const ParticleMap& _map;
+        const std::string _particleId;
         const float _scale;
 
         GLuint _vbo;
         GLuint _vao;
         std::vector<float> _vertices;
 
-        void regenerateVertices();
+        void regenerateVertices(const glm::vec3& basePos);
 };