From 0f990eb95a9ef3a1be8847a863f7216a8625692a Mon Sep 17 00:00:00 2001
From: Brian Cully <bjc@spork.org>
Date: Thu, 18 Dec 2025 20:28:53 -0500
Subject: add bouncing when hitting arena edge

---
 site/main.mjs       | 30 ++++++++++++++++++++++++++++--
 site/robo.mjs       |  3 +++
 site/samples/rob.fs |  2 +-
 src/forth/vm.rs     |  6 +++---
 src/lib.rs          |  8 ++++++++
 5 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/site/main.mjs b/site/main.mjs
index 31f1375..703062d 100644
--- a/site/main.mjs
+++ b/site/main.mjs
@@ -112,8 +112,7 @@ function renderArena(robos, delta=0.0) {
             robo.speedx, robo.speedy
         ].map(x => timeScale * x);
 
-        const x = robo.x + velx;
-        const y = robo.y + vely;
+        const [_, x, y] = bounce(25, robo.heading, robo.x + velx, robo.y + vely, canvas.width, canvas.height);
         //console.debug('bjc render robo', robo, velx, vely, x, y)
         renderRobo(ctx, x, y);
     });
@@ -154,6 +153,26 @@ function loadForth(taintedPath) {
         });
 }
 
+function bounce(radius, heading, x, y, width, height) {
+    // todo: don't just clamp the x/y, instead calculate based on
+    // where the intersection with the wall is.
+    if (y < radius) {
+        // top wall
+        return [-1 * heading, x, radius];
+    } else if (y >= height-radius) {
+        // bottom wall
+        return [-1 * heading, x, height-radius];
+    } else if (x < radius) {
+        // left wall
+        return [heading - 180, radius, y];
+    } else if (x >= width-radius) {
+        // right wall
+        return [180 - heading, width-radius, y];
+    } else {
+        return [heading, x, y];
+    }
+}
+
 async function loaded() {
     const roboWorker = new Worker('robo.mjs', { type: 'module' });
     const robo = {
@@ -206,6 +225,13 @@ async function loaded() {
             robo.speedy = speedy;
             robo.x += speedx;
             robo.y += speedy;
+            const canvas = document.querySelector(CANVAS_SELECTOR);
+            const [newHeading, newx, newy] = bounce(25, trans.vars.heading, robo.x, robo.y, canvas.width, canvas.height);
+            if (newHeading != trans.vars.heading) {
+                roboWorker.postMessage({ kind: 'setHeading', heading: newHeading });
+                robo.x = newx;
+                robo.y = newy;
+            }
             renderArena([robo]);
             break;
         default:
diff --git a/site/robo.mjs b/site/robo.mjs
index 1b7c3d8..d80baad 100644
--- a/site/robo.mjs
+++ b/site/robo.mjs
@@ -26,6 +26,9 @@ async function messageHandler(e) {
     case 'tick':
         tick();
         break;
+    case 'setHeading':
+        vm.setheading(e.data.heading);
+        break;
     default:
         console.error('invalid message to robo worker', e.data);
         postMessage({ kind: 'error', error: 'badmsg' });
diff --git a/site/samples/rob.fs b/site/samples/rob.fs
index 32112d4..59dc946 100644
--- a/site/samples/rob.fs
+++ b/site/samples/rob.fs
@@ -3,5 +3,5 @@
 	loop
 ;
 
-4 setspeed
+7 setspeed
 loop
diff --git a/src/forth/vm.rs b/src/forth/vm.rs
index 564a647..25ed516 100644
--- a/src/forth/vm.rs
+++ b/src/forth/vm.rs
@@ -4,9 +4,9 @@ use std::ops::Index;
 
 pub type DataStackType = isize;
 
-const MIN_SPEED: DataStackType = 0;
-const MAX_SPEED: DataStackType = 10;
-const UNITS_PER_ROTATION: DataStackType = 360;
+pub const MIN_SPEED: DataStackType = 0;
+pub const MAX_SPEED: DataStackType = 10;
+pub const UNITS_PER_ROTATION: DataStackType = 360;
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum OpCode {
diff --git a/src/lib.rs b/src/lib.rs
index 2aedfff..240acf1 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -135,6 +135,14 @@ impl ExportedVM {
         vm.ip.offset = 0;
     }
 
+    pub fn setheading(&mut self, v: forth::vm::DataStackType) {
+        let Some(vm) = &mut self.vm else {
+            return;
+        };
+        use forth::vm::UNITS_PER_ROTATION;
+        vm.heading = (UNITS_PER_ROTATION + (v % UNITS_PER_ROTATION)) % UNITS_PER_ROTATION;
+    }
+
     pub fn trans(&mut self) -> Result<js_sys::Object, JsValue> {
         let vm = (&mut self.vm).as_mut().ok_or(Error::NoVM)?;
         let res = js_sys::Map::new();
-- 
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