From cf67842d24609612c49fd5f2f847e374a8b2be99 Mon Sep 17 00:00:00 2001
From: Thom Bruce <thom@thombruce.com>
Date: Sat, 28 Oct 2023 23:08:30 +0100
Subject: [PATCH] generalise dynamic_orbit for any kind of entity with new
 Gravitable component

---
 CHANGELOG.md               |  4 ++++
 src/ships/bullet.rs        | 18 +++++++++++++++++-
 src/ships/dynamic_orbit.rs |  5 +++--
 src/ships/enemy.rs         |  2 ++
 src/ships/player.rs        |  2 ++
 5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9d25787..e077e53 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Gravitable component added allowing dynamic_orbit system to be applied to any entity
+
 ### Fixed
 
 - follow_player camera system now constrained to .after() player movement
diff --git a/src/ships/bullet.rs b/src/ships/bullet.rs
index 6d1c0d5..e0c2e65 100644
--- a/src/ships/bullet.rs
+++ b/src/ships/bullet.rs
@@ -7,7 +7,8 @@ use crate::core::resources::{
     state::{ForState, GameState},
 };
 
-use super::ship::MovementSet;
+#[allow(unused_imports)]
+use super::{dynamic_orbit::Gravitable, ship::MovementSet};
 
 #[derive(Component)]
 pub struct Bullet;
@@ -62,6 +63,21 @@ fn spawn_bullet(
                 ..default()
             },
             Bullet,
+            // TODO: Should bullets be affected by gravity?
+            //       If so, set their initial velocity higher and consider
+            //       despawning them either based on distance or a longer
+            //       timer. Systems as they are, it's far too ridiculous and
+            //       highly unpredictable.
+            //       A bullet speed of around 5000.0 is a reasonable demo of the effect.
+            //       But think again about despawning based on distance - this would mean
+            //       the player could spawn millions of bullets inside of a gravitational
+            //       well and never have them despawn. There has to be a limit to either
+            //       the entity lifetime or the entity count.
+            //       Also consider an alternative to adjusting bullet's speed:
+            //       - introduce a gravitational scaling factor that may be unique per entity
+            //       This might be unrealistic, but it might make for better gameplay.
+            // Gravitable,
+            // ExternalImpulse::default(),
             DespawnTimer(Timer::from_seconds(2.0, TimerMode::Once)),
             ForState {
                 states: GameState::IN_GAME_STATE.to_vec(),
diff --git a/src/ships/dynamic_orbit.rs b/src/ships/dynamic_orbit.rs
index 589778f..aeb90a2 100644
--- a/src/ships/dynamic_orbit.rs
+++ b/src/ships/dynamic_orbit.rs
@@ -7,7 +7,8 @@ use crate::{
     world::{astronomy::orbit::Mass, spatial::KDNode},
 };
 
-use super::ship::Ship;
+#[derive(Component)]
+pub struct Gravitable;
 
 pub struct DynamicOrbitPlugin;
 impl Plugin for DynamicOrbitPlugin {
@@ -21,7 +22,7 @@ impl Plugin for DynamicOrbitPlugin {
 
 pub fn dynamic_orbital_positioning_system(
     tree: Res<KDTree2<KDNode>>,
-    mut query: Query<(&Transform, &mut ExternalImpulse), With<Ship>>,
+    mut query: Query<(&Transform, &mut ExternalImpulse), With<Gravitable>>,
     masses: Query<&Mass, With<KDNode>>,
 ) {
     for (transform, mut impulse) in query.iter_mut() {
diff --git a/src/ships/enemy.rs b/src/ships/enemy.rs
index 7bf708c..077e685 100644
--- a/src/ships/enemy.rs
+++ b/src/ships/enemy.rs
@@ -4,6 +4,7 @@ use bevy_rapier2d::prelude::*;
 use crate::core::resources::{assets::SpriteAssets, state::GameState};
 use crate::ui::hud::indicator::Indicated;
 
+use super::dynamic_orbit::Gravitable;
 use super::{
     bullet::BulletSpawnEvent,
     player::Player,
@@ -57,6 +58,7 @@ fn setup(mut commands: Commands, sprites: Res<SpriteAssets>) {
                 rotation: f32::to_radians(360.0), // Ship manoeuvrability (rad)
                 bullet_timer: Timer::from_seconds(0.1, TimerMode::Once),
             },
+            Gravitable,
             Health(1000.0),
             Indicated { color: Color::RED },
             SpriteBundle {
diff --git a/src/ships/player.rs b/src/ships/player.rs
index 9c99a86..caed860 100644
--- a/src/ships/player.rs
+++ b/src/ships/player.rs
@@ -9,6 +9,7 @@ use crate::{
 
 use super::{
     bullet::BulletSpawnEvent,
+    dynamic_orbit::Gravitable,
     ship::{dampening, ship_rotation, ship_thrust, AttackSet, Health, MovementSet, Ship},
 };
 
@@ -43,6 +44,7 @@ fn setup(mut commands: Commands, sprites: Res<SpriteAssets>) {
             rotation: f32::to_radians(360.0), // Ship manoeuvrability (rad)
             bullet_timer: Timer::from_seconds(0.1, TimerMode::Once),
         },
+        Gravitable,
         Health(10000.0), // TODO: Game balancing
         SpriteBundle {
             texture: sprites.player_ship.clone(),