display local position and velocity for children of bodies

src/renderer.cpp

@@ -548,6 +548,7 @@ void render_body_info_ui(SimulationState* sim, RenderState* render_state) {
     strcat(info_text, "\n");
     strcat(info_text, temp_buffer);
 
+    if (body->parent_index <= 0) {
         // Position
         snprintf(temp_buffer, sizeof(temp_buffer), "Position: (%.2e, %.2e, %.2e)",
                  body->position.x, body->position.y, body->position.z);
@@ -559,6 +560,20 @@ void render_body_info_ui(SimulationState* sim, RenderState* render_state) {
         snprintf(temp_buffer, sizeof(temp_buffer), "Velocity: %.2f m/s", vel_mag);
         strcat(info_text, "\n");
         strcat(info_text, temp_buffer);
+    } else {
+        // Position (Local)
+        snprintf(temp_buffer, sizeof(temp_buffer), "local_position: (%.2e, %.2e, %.2e)",
+                 body->local_position.x, body->local_position.y, body->local_position.z);
+        strcat(info_text, "\n");
+        strcat(info_text, temp_buffer);
+
+        // Velocity (Local)
+        double parent_vel_mag = vec3_magnitude(sim->bodies[body->parent_index].velocity);
+        double vel_mag = vec3_magnitude(body->velocity) - parent_vel_mag;
+        snprintf(temp_buffer, sizeof(temp_buffer), "local_velocity: %.2f m/s", vel_mag);
+        strcat(info_text, "\n");
+        strcat(info_text, temp_buffer);
+    }
 
     // Orbital elements
     snprintf(temp_buffer, sizeof(temp_buffer), "Eccentricity: %.3f", body->eccentricity);