From a80c925543e1d65648c99f26f5e9e7171a8d3a2f Mon Sep 17 00:00:00 2001
From: Brendan Reville <brendan@code.org>
Date: Fri, 25 Oct 2019 14:00:21 -0700
Subject: [PATCH] Ease fish movement animations

---
 src/demo/renderer.js | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/demo/renderer.js b/src/demo/renderer.js
index 384b2d86..c157e5c7 100644
--- a/src/demo/renderer.js
+++ b/src/demo/renderer.js
@@ -162,11 +162,17 @@ const finishMovement = () => {
 
 // Calculate the screen's current X offset.
 const getOffsetForTime = (t, totalFish) => {
+  // Normalize the fish movement amount from 0 to 1.
+  let amount = t / moveTime;
+
+  // Apply an S-curve to that amount.
+  amount = amount - Math.sin(amount*2*Math.PI) / (2*Math.PI);
+
   return (
     constants.fishCanvasWidth * totalFish -
     constants.canvasWidth / 2 +
     constants.fishCanvasWidth / 2 -
-    Math.round((t * constants.fishCanvasWidth) / moveTime)
+    Math.round(amount * constants.fishCanvasWidth)
   );
 };