add FIXMEs, and update manual TODO

docs/TODO

@@ -13,6 +13,9 @@ If you see modifications to this file in git status, IGNORE them and do not comm
         frame. we need to test, and make a compromise on performance vs sim
         accuracy, and have this set as a config constant, MAX_STEP_SIZE, with
         a good discription nearby in the code.
+    - see FIXMEs in simulation.cpp, and physics.cpp about not simulating root
+        bodies anymore
+    - remove simulation dependancy from physics.h
     - fix moon tests with SOI coordinate transforms for planets
     - remove bodies on non closed orbits after they are a certain distance from
         the root body, or bary-center

src/physics.cpp

@@ -77,6 +77,7 @@ Vec3 evaluate_acceleration(Vec3 pos, Vec3 vel, AccelerationContext* ctx) {
 
     Vec3 total_force = {0.0, 0.0, 0.0};
 
+    // FIXME: we shouldn't be simulating root bodies anymore
     if (temp_body.parent_index == -1) {
         for (int j = 0; j < ctx->sim->body_count; j++) {
             if (j == ctx->body_index) continue;
@@ -89,12 +90,12 @@ Vec3 evaluate_acceleration(Vec3 pos, Vec3 vel, AccelerationContext* ctx) {
     } else {
         if (temp_body.parent_index >= 0 && temp_body.parent_index < ctx->sim->body_count) {
             CelestialBody* parent = &ctx->sim->bodies[temp_body.parent_index];
-            
+
             double distance = vec3_magnitude(pos);
             if (distance < 1.0) {
                 distance = 1.0;
             }
-            
+
             double force_magnitude = G * temp_body.mass * parent->mass / (distance * distance);
             Vec3 direction = vec3_normalize(vec3_scale(pos, -1.0));
             total_force = vec3_scale(direction, force_magnitude);

src/simulation.cpp

@@ -79,6 +79,7 @@ void update_simulation(SimulationState* sim) {
     for (int i = 0; i < sim->body_count; i++) {
         CelestialBody* body = &sim->bodies[i];
 
+        // FIXME: we shouldn't be simulating root bodies anymore
         if (body->parent_index == -1) {
             AccelerationContext ctx;
             ctx.sim = sim;
@@ -219,6 +220,8 @@ void compute_global_coordinates(SimulationState* sim) {
         if (body->parent_index == -1) {
             body->position = body->local_position;
             body->velocity = body->local_velocity;
+        // FIXME: parent_index > body_count is an error in config file, we
+        //  should either verify that in config_loader, or have an assert here
         } else if (body->parent_index >= 0 && body->parent_index < sim->body_count) {
             CelestialBody* parent = &sim->bodies[body->parent_index];
             body->position = vec3_add(body->local_position, parent->position);