Add orbit path visualization with sim-to-render coordinate transform

🤖 Generated with Claude Code - Co-Authored-By: Claude Sonnet 4.5

src/bodies.cpp

@@ -26,7 +26,8 @@ void destroy_simulation(SimulationState* sim) {
 
 // Add a celestial body to the simulation
 void add_body(SimulationState* sim, const char* name, double mass, double radius,
-              Vec3 pos, Vec3 vel, int parent_index, float r, float g, float b) {
+              Vec3 pos, Vec3 vel, int parent_index, float r, float g, float b,
+              double eccentricity, double semi_major_axis) {
     if (sim->body_count >= sim->max_bodies) {
         return;  // No more space
     }
@@ -43,6 +44,8 @@ void add_body(SimulationState* sim, const char* name, double mass, double radius
     body->color[0] = r;
     body->color[1] = g;
     body->color[2] = b;
+    body->eccentricity = eccentricity;
+    body->semi_major_axis = semi_major_axis;
 
     sim->body_count++;
 }

src/bodies.h

@@ -13,6 +13,8 @@ struct CelestialBody {
     double soi_radius;        // sphere of influence radius (meters)
     int parent_index;         // index of gravitational parent (-1 for root body like Sun)
     float color[3];           // RGB color for rendering
+    double eccentricity;      // orbital eccentricity (0 = circular, <1 = elliptical)
+    double semi_major_axis;   // meters
 };
 
 // Simulation state
@@ -28,7 +30,8 @@ struct SimulationState {
 SimulationState* create_simulation(int max_bodies, double time_step);
 void destroy_simulation(SimulationState* sim);
 void add_body(SimulationState* sim, const char* name, double mass, double radius,
-              Vec3 pos, Vec3 vel, int parent_index, float r, float g, float b);
+              Vec3 pos, Vec3 vel, int parent_index, float r, float g, float b,
+              double eccentricity, double semi_major_axis);
 
 // SOI and simulation update functions
 int find_dominant_body(SimulationState* sim, int body_index);

src/config_loader.cpp

@@ -50,7 +50,8 @@ bool load_system_config(SimulationState* sim, const char* filepath) {
         if (parse_body_line(line, name, &mass, &radius, &pos, &parent_index, &r, &g, &b,
                            &eccentricity, &semi_major_axis)) {
             Vec3 vel = {0.0, 0.0, 0.0};
-            add_body(sim, name, mass, radius, pos, vel, parent_index, r, g, b);
+            add_body(sim, name, mass, radius, pos, vel, parent_index, r, g, b,
+                    eccentricity, semi_major_axis);
 
             orbit_params[sim->body_count - 1].eccentricity = eccentricity;
             orbit_params[sim->body_count - 1].semi_major_axis = semi_major_axis;

src/renderer.cpp

@@ -70,12 +70,13 @@ void update_camera(RenderState* render_state) {
     }
 }
 
-// Scale a position for rendering
-Vector3 scale_position(Vec3 pos, double scale) {
+// Transform from simulation coordinates (XY plane) to render coordinates (XZ plane)
+// Rotation matrix: 90 degrees around X-axis maps Y -> Z
+Vector3 sim_to_render(Vec3 pos, double scale) {
     return (Vector3){
         (float)(pos.x * scale),
-        (float)(pos.y * scale),
-        (float)(pos.z * scale)
+        (float)(-pos.z * scale),
+        (float)(pos.y * scale)
     };
 }
 
@@ -88,17 +89,76 @@ float scale_radius(double radius, double scale) {
 
 // Render a single celestial body
 void render_body(CelestialBody* body, RenderState* render_state) {
-    Vector3 position = scale_position(body->position, render_state->distance_scale);
+    Vector3 position = sim_to_render(body->position, render_state->distance_scale);
     float radius = scale_radius(body->radius, render_state->size_scale);
 
+    float r = body->color[0];
+    float g = body->color[1];
+    float b = body->color[2];
+
+    if (body->parent_index == -1) {
+        float gray = (r + g + b) / 3.0f * 0.3f;
+        r = g = b = gray;
+    }
+
     Color color = {
-        (unsigned char)(body->color[0] * 255),
-        (unsigned char)(body->color[1] * 255),
-        (unsigned char)(body->color[2] * 255),
+        (unsigned char)(r * 255),
+        (unsigned char)(g * 255),
+        (unsigned char)(b * 255),
         255
     };
 
-    DrawSphere(position, radius, color);
+    DrawSphereWires(position, radius, 16, 16, color);
+}
+
+// Render orbit path for a body
+void render_orbit(CelestialBody* body, CelestialBody* parent, RenderState* render_state) {
+    if (body->parent_index == -1 || parent == NULL) {
+        return;
+    }
+
+    double a = body->semi_major_axis;
+    double e = body->eccentricity;
+
+    if (a <= 0.0) {
+        return;
+    }
+
+    double b = a * sqrt(1.0 - e * e);
+    double c = a * e;
+
+    Vector3 parent_pos = sim_to_render(parent->position, render_state->distance_scale);
+
+    Color orbit_color = {
+        (unsigned char)(body->color[0] * 128),
+        (unsigned char)(body->color[1] * 128),
+        (unsigned char)(body->color[2] * 128),
+        128
+    };
+
+    int segments = 100;
+    for (int i = 0; i < segments; i++) {
+        float theta1 = (float)i / segments * 2.0f * PI;
+        float theta2 = (float)(i + 1) / segments * 2.0f * PI;
+
+        float x1 = (float)(a * cos(theta1) - c);
+        float y1 = (float)(b * sin(theta1));
+        float x2 = (float)(a * cos(theta2) - c);
+        float y2 = (float)(b * sin(theta2));
+
+        Vector3 p1 = {
+            parent_pos.x + x1 * (float)render_state->distance_scale,
+            parent_pos.y,
+            parent_pos.z + y1 * (float)render_state->distance_scale
+        };
+        Vector3 p2 = {
+            parent_pos.x + x2 * (float)render_state->distance_scale,
+            parent_pos.y,
+            parent_pos.z + y2 * (float)render_state->distance_scale
+        };
+
+        DrawLine3D(p1, p2, orbit_color);
+    }
 }
 
 // Render the entire simulation
@@ -108,8 +168,27 @@ void render_simulation(SimulationState* sim, RenderState* render_state) {
 
     BeginMode3D(render_state->camera);
 
-    // Draw a reference grid
-    DrawGrid(100, 10.0f);
+    // Draw a subtle reference grid
+    for (int i = -50; i <= 50; i++) {
+        if (i == 0) continue;
+        DrawLine3D((Vector3){(float)i * 10.0f, 0, -500.0f},
+                   (Vector3){(float)i * 10.0f, 0, 500.0f},
+                   (Color){20, 20, 20, 255});
+        DrawLine3D((Vector3){-500.0f, 0, (float)i * 10.0f},
+                   (Vector3){500.0f, 0, (float)i * 10.0f},
+                   (Color){20, 20, 20, 255});
+    }
+    DrawLine3D((Vector3){0, 0, -500.0f}, (Vector3){0, 0, 500.0f}, (Color){40, 40, 40, 255});
+    DrawLine3D((Vector3){-500.0f, 0, 0}, (Vector3){500.0f, 0, 0}, (Color){40, 40, 40, 255});
+
+    // Render orbit paths first
+    for (int i = 0; i < sim->body_count; i++) {
+        CelestialBody* body = &sim->bodies[i];
+        if (body->parent_index >= 0 && body->parent_index < sim->body_count) {
+            CelestialBody* parent = &sim->bodies[body->parent_index];
+            render_orbit(body, parent, render_state);
+        }
+    }
 
     // Render all bodies
     for (int i = 0; i < sim->body_count; i++) {