From 01c5d765869d2630ba12266d579145001ba4b22e Mon Sep 17 00:00:00 2001
From: JP Stringham <jp@bloomdigital.to>
Date: Sat, 7 Feb 2026 18:15:14 -0500
Subject: [PATCH] some physics

---
 src/main.rs    | 72 +++++++++++++++++++++++++++++++++++++++++++-------
 src/physics.rs |  0
 src/player.rs  |  8 ++++--
 3 files changed, 68 insertions(+), 12 deletions(-)
 create mode 100644 src/physics.rs

diff --git a/src/main.rs b/src/main.rs
index 46dc0f4..1f30823 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,7 +1,8 @@
 mod ldtk;
+mod physics;
 mod player;
 
-use bevy::{image::Image, prelude::*};
+use bevy::{image::Image, math::I64Vec2, prelude::*};
 
 use crate::player::Player;
 
@@ -140,9 +141,9 @@ fn levelload(
         }
 
         li.entities.iter().for_each(|ei| {
-            let pos = IVec2 {
-                x: ei.position.x * 16,
-                y: 256 - ei.position.y * 16,
+            let pos = I64Vec2 {
+                x: ei.position.x as i64 * 16,
+                y: 256 - ei.position.y as i64 * 16,
             };
             let mut spawned_ent = commands.spawn((
                 Name::from(ei.identifier.clone()),
@@ -150,7 +151,10 @@ fn levelload(
             ));
             match ei.identifier.as_str() {
                 "Player" => {
-                    spawned_ent.insert(Player { pos });
+                    spawned_ent.insert(Player {
+                        pos,
+                        vel: I64Vec2::ZERO,
+                    });
                     spawned_ent.insert(Sprite::from_color(Color::WHITE, vec2(16., 16.)));
                 }
                 "Parsnip" => {
@@ -167,8 +171,13 @@ fn levelload(
     next_state.set(AppState::Main);
 }
 
-fn gameloop(keyb: Res<ButtonInput<KeyCode>>, mut player: Single<(&mut Player, &mut Transform)>) {
-    let mut dir = IVec2::ZERO;
+fn gameloop(
+    keyb: Res<ButtonInput<KeyCode>>,
+    mut player_sing: Single<(&mut Player, &mut Transform)>,
+) {
+    const UNITS_TO_PX_SCALE: i64 = 100;
+    const MAX_SPEED: i64 = 2 * UNITS_TO_PX_SCALE;
+    let mut dir = I64Vec2::ZERO;
 
     if keyb.pressed(KeyCode::KeyA) || keyb.pressed(KeyCode::ArrowLeft) {
         dir.x += -1;
@@ -186,8 +195,51 @@ fn gameloop(keyb: Res<ButtonInput<KeyCode>>, mut player: Single<(&mut Player, &m
         dir.y = -1;
     }
 
-    let p_pos = player.0.pos + dir;
-    player.0.pos = p_pos;
+    let player = player_sing.0.as_mut();
 
-    *player.1 = Transform::from_xyz(p_pos.x as f32, p_pos.y as f32, 100.);
+    // player vel and pos are in px / 100
+    let mut p_vel = player.vel + dir * UNITS_TO_PX_SCALE * MAX_SPEED;
+    if dir.length_squared() == 0 {
+        p_vel = (p_vel * 8) / 10;
+        info!("Slowing! {p_vel}");
+    } else {
+        info!("Changing vel: {p_vel}")
+    }
+
+    // want unit vector with int math
+    // normally this would be x / len, y / len
+
+    // eg (2,2) -> length of 4 -> (0.5, 0.5)
+    // how to do with squares?
+
+    // (2, 2) -> sqr length of 8 -> sqr x / 8 -> 0.5... yes?
+    // but we can't get half units obvs so we need to work in centi-units
+    // 200, 200 -> should become 50, 50
+
+    // max speed is 3 px per update
+    if p_vel.length_squared() >= MAX_SPEED.pow(2) {
+        let l = p_vel.length_squared();
+        let x = p_vel.x * p_vel.x;
+        let y = p_vel.y * p_vel.y;
+
+        p_vel.x = match p_vel.x {
+            ..0 => (x * -MAX_SPEED) / l,
+            _ => (x * MAX_SPEED) / l,
+        };
+        p_vel.y = match p_vel.y {
+            ..0 => (y * -MAX_SPEED) / l,
+            _ => (y * MAX_SPEED) / l,
+        };
+
+        info!("Nerfed speed {p_vel}");
+    }
+
+    player.vel = p_vel;
+    player.pos += p_vel;
+
+    *player_sing.1 = Transform::from_xyz(
+        (player.pos.x as f32) / UNITS_TO_PX_SCALE as f32,
+        (player.pos.y as f32) / UNITS_TO_PX_SCALE as f32,
+        100.,
+    );
 }
diff --git a/src/physics.rs b/src/physics.rs
new file mode 100644
index 0000000..e69de29
diff --git a/src/player.rs b/src/player.rs
index 74ed61a..9888ff3 100644
--- a/src/player.rs
+++ b/src/player.rs
@@ -1,6 +1,10 @@
-use bevy::{ecs::component::Component, math::IVec2};
+use bevy::{
+    ecs::component::Component,
+    math::{I64Vec2, IVec2},
+};
 
 #[derive(Default, Debug, Component)]
 pub struct Player {
-    pub pos: IVec2,
+    pub pos: I64Vec2,
+    pub vel: I64Vec2,
 }