From bcb38594492aec4f1116b3fdf0e9821d4016903a Mon Sep 17 00:00:00 2001
From: Arjun Satarkar <me@arjunsatarkar.net>
Date: Wed, 30 Oct 2024 22:27:17 -0400
Subject: Implement the physics

---
 src/index.js | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 src/index.js

(limited to 'src/index.js')

diff --git a/src/index.js b/src/index.js
new file mode 100644
index 0000000..1275360
--- /dev/null
+++ b/src/index.js
@@ -0,0 +1,94 @@
+import RAPIER from "./rapier.es.js";
+
+RAPIER.init().then(() => {
+  const CLICK_IMPULSE_MULTIPLIER = 300_000;
+  const GRAVITY = { x: 0.0, y: 2000 };
+  const LINEAR_DAMPING = 0.5;
+  const OBJ_BASE_RADIUS = 30;
+  const OBJ_BASE_SIZE = { x: OBJ_BASE_RADIUS * 2, y: OBJ_BASE_RADIUS * 2 };
+  const OBJ_MASS = 100;
+  const STEP_MS = 33;
+  const TARGET_WIDTH_FACTOR = 0.05;
+  const VIEWPORT_SIZE = {
+    x: document.documentElement.clientWidth,
+    y: document.documentElement.clientHeight,
+  };
+  const WIDTH_JUMP_FACTOR = 5;
+
+  let world = new RAPIER.World(GRAVITY);
+
+  const wallColliderDescs = {
+    x: RAPIER.ColliderDesc.cuboid(VIEWPORT_SIZE.x, 1).setRestitution(1),
+    y: RAPIER.ColliderDesc.cuboid(1, VIEWPORT_SIZE.y).setRestitution(1),
+  };
+  world.createCollider(wallColliderDescs.x);
+  world.createCollider(wallColliderDescs.x.setTranslation(0, VIEWPORT_SIZE.y));
+  world.createCollider(wallColliderDescs.y);
+  world.createCollider(wallColliderDescs.y.setTranslation(VIEWPORT_SIZE.x, 0));
+
+  let objRigidBodyDesc = RAPIER.RigidBodyDesc.dynamic()
+    .setTranslation(VIEWPORT_SIZE.x / 2, VIEWPORT_SIZE.y / 3)
+    .setLinearDamping(LINEAR_DAMPING)
+    .setCcdEnabled(true);
+  let obj = world.createRigidBody(objRigidBodyDesc);
+  world.createCollider(
+    RAPIER.ColliderDesc.ball(OBJ_BASE_RADIUS).setMass(OBJ_MASS),
+    obj,
+  );
+
+  const objElement = document.querySelector("div#throwable");
+  const objSize = {
+    x: OBJ_BASE_SIZE.x,
+    y: OBJ_BASE_SIZE.y,
+  };
+  let objVelocityLastFrame = null;
+
+  let mainLoop = () => {
+    world.step();
+
+    const objPosition = obj.translation();
+    objElement.style.left = `${objPosition.x}px`;
+    objElement.style.top = `${objPosition.y}px`;
+
+    const objVelocity = obj.linvel();
+    if (objVelocityLastFrame !== null) {
+      // Just delta velocity across a frame, technically
+      const objAcceleration = {
+        x: objVelocity.x - objVelocityLastFrame.x,
+        y: objVelocity.y - objVelocityLastFrame.y,
+      };
+      let targetWidth =
+        OBJ_BASE_SIZE.x + TARGET_WIDTH_FACTOR * Math.abs(objAcceleration.y);
+      let targetHeight =
+        OBJ_BASE_SIZE.y + TARGET_WIDTH_FACTOR * Math.abs(objAcceleration.x);
+
+      objSize.x = objSize.x + (targetWidth - objSize.x) / WIDTH_JUMP_FACTOR;
+      objSize.y = objSize.y + (targetHeight - objSize.y) / WIDTH_JUMP_FACTOR;
+    }
+    objVelocityLastFrame = objVelocity;
+
+    objElement.style.width = `${objSize.x}px`;
+    objElement.style.height = `${objSize.y}px`;
+
+    setTimeout(mainLoop, STEP_MS);
+  };
+
+  document.addEventListener("click", (e) => {
+    const clickPosition = { x: e.clientX, y: e.clientY };
+    const objPosition = obj.translation();
+    const direction = {
+      x: clickPosition.x - objPosition.x,
+      y: clickPosition.y - objPosition.y,
+    };
+    const distance = Math.sqrt(direction.x ** 2 + direction.y ** 2);
+    obj.setLinvel({x: 0, y: 0});
+    if (distance > 0) {
+      obj.applyImpulse({
+        x: (direction.x * CLICK_IMPULSE_MULTIPLIER) / distance,
+        y: (direction.y * CLICK_IMPULSE_MULTIPLIER) / distance,
+      });
+    }
+  });
+
+  mainLoop();
+});
-- 
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