diff --git a/index.html b/index.html
index 90675b2..569870e 100644
--- a/index.html
+++ b/index.html
@@ -30,24 +30,24 @@
         padding: 5px;
         /* color: red; */
       }
-      .menu div {
+      .obstacle {
         width: 110px;
         background-color: silver;
         margin: 3px;
         padding: 2px;
         user-select: none;
       }
-      .menu div:hover {
+      .obstacle:hover {
         color: white;
       }
-      .menu div:active {
+      .obstacle:active {
         background-color: black;
       }
       .active {
         background-color: black !important;
         color: white;
       }
-      #debug {
+      input {
         margin: 5px;
       }
     </style>
@@ -62,10 +62,11 @@
     </div>
     <div id="mode" class="hint"></div>
     <div id="menu" class="menu">
-      <div id="rect" onclick="ChangeObstacle(this.id)">Rectangle</div>
-      <div id="square" onclick="ChangeObstacle(this.id)">Rounded</div>
-      <div id="force" onclick="ChangeObstacle(this.id)">Force Field</div>
-      <input type="checkbox" name="debug" id="debug" onclick="updateDebug(this.checked)"><label for="debug">debug</label>
+      <div id="rect" class="obstacle" onclick="ChangeObstacle(this.id)">Rectangle</div>
+      <div id="square" class="obstacle" onclick="ChangeObstacle(this.id)">Rounded</div>
+      <div id="force" class="obstacle" onclick="ChangeObstacle(this.id)">Force Field</div>
+      <div><input type="checkbox" name="shading" id="shading" onclick="updateShading(this.checked)"><label for="shading">shading</label></div>
+      <div><input type="checkbox" name="debug" id="debug" onclick="updateDebug(this.checked)"><label for="debug">debug</label></div>
     </div>
     <script type="module" src="./src/game.js"></script>
 
diff --git a/src/game.js b/src/game.js
index 012e829..d1e223b 100644
--- a/src/game.js
+++ b/src/game.js
@@ -3,8 +3,8 @@ import { runSim, addBall, addForceField, addRectangle, addSquare } from './simul
 const canvas = document.getElementById('myCanvas')
 export const ctx = canvas.getContext('2d')
 
-let xMouse = 0
-let yMouse = 0
+export let xMouse = 0
+export let yMouse = 0
 let xLastMouse = 0
 let yLastMouse = 0
 let xMouseStartDrag = 0
@@ -15,7 +15,8 @@ let height = 10
 
 let mode = 2 // 1:bubbles, 2:rigid
 let obstacle = ''
-let drag = false
+export let drag = false
+export let mousedown = false
 
 resizeCanvas()
 
@@ -38,6 +39,7 @@ function drawObstacle () {
 window.ChangeObstacle = ChangeObstacle
 
 canvas.addEventListener('mousedown', (evt) => {
+  mousedown = true
   xMouseStartDrag = xMouse
   yMouseStartDrag = yMouse
 
@@ -61,6 +63,7 @@ window.addEventListener('mousemove', (evt) => {
 }, false)
 
 window.addEventListener('mouseup', (evt) => {
+  mousedown = false
   if (drag) {
     drag = false
     switch (obstacle) {
diff --git a/src/simulation.js b/src/simulation.js
index 9925f65..eadbd7d 100644
--- a/src/simulation.js
+++ b/src/simulation.js
@@ -1,5 +1,5 @@
 import { Ball, ForceField, Rectangle, Square } from './library.js'
-import { ctx } from './game.js'
+import { ctx, xMouse, yMouse, mousedown, drag } from './game.js'
 
 const balls = []
 const ForceFields = []
@@ -7,15 +7,25 @@ const rectangles = []
 const squares = []
 const force = 0.01
 let BallCount = 0
+let shading = false
 let debug = false
+let changelight = false
+const lightAngle = [-0.4, -0.4]
 
 function updateDebug (flag) {
   debug = flag
 }
 window.updateDebug = updateDebug
 
+function updateShading (flag) {
+  shading = flag
+}
+window.updateShading = updateShading
+
 export function runSim (xMouseVec, yMouseVec, width, height, mode) {
-  BallMove(xMouseVec, yMouseVec)
+  if (!drag && !changelight) {
+    BallMove(xMouseVec, yMouseVec)
+  }
   ForceFieldsImpact()
   BallBallCollision(mode)
   BallWallCollision(width, height)
@@ -23,9 +33,65 @@ export function runSim (xMouseVec, yMouseVec, width, height, mode) {
   BallSquareCollision()
 
   drawForceFields()
+  if (shading) {
+    drawBallShadows()
+  }
   drawBalls()
   drawRectangles()
   drawSquares()
+
+  if (shading) {
+    drawLightPicker()
+  }
+}
+
+function drawLightPicker () {
+  const radius = 40
+  const x = 50
+  const y = 200
+  let xOff = radius * lightAngle[0]
+  let yOff = radius * lightAngle[1]
+
+  if (mousedown && !drag) {
+    const vector = Math.hypot(xMouse - x, yMouse - y)
+
+    if (vector < radius) {
+      changelight = true
+    }
+
+    const xLimit = ((xMouse - x) / vector) * (radius - 10)
+    const yLimit = ((yMouse - y) / vector) * (radius - 10)
+
+    if (changelight) {
+      xOff = xMouse - x
+      yOff = yMouse - y
+
+      // limits movement range of yellow picker
+      if ((xOff > 0 && xOff > xLimit) || (xOff < 0 && xOff < xLimit)) {
+        xOff = xLimit
+      }
+      if ((yOff > 0 && yOff > yLimit) || (yOff < 0 && yOff < yLimit)) {
+        yOff = yLimit
+      }
+
+      lightAngle[0] = xOff / radius
+      lightAngle[1] = yOff / radius
+    }
+  } else {
+    changelight = false
+  }
+
+  ctx.beginPath()
+  ctx.arc(x, y, radius, 0, 6.2831)
+  ctx.fillStyle = 'grey'
+  ctx.fill()
+  ctx.closePath()
+
+  ctx.beginPath()
+  ctx.arc(x + xOff, y + yOff, 10, 0, 6.2831)
+  ctx.fillStyle = 'yellow'
+  ctx.fill()
+  ctx.closePath()
 }
 
 export function addBall () {
@@ -386,15 +452,57 @@ function drawBalls () {
     drawBall(balls[i].x, balls[i].y, balls[i].radius, balls[i].color)
   }
 }
+function drawBallShadows () {
+  for (let i = 0; i < BallCount; i++) {
+    drawBallShadow(balls[i].x, balls[i].y, balls[i].radius)
+  }
+}
+
+function drawBallShadow (x, y, radius) {
+  const offsetX = radius * -lightAngle[0] * 0.4
+  const offsetY = radius * -lightAngle[1] * 0.4
+  ctx.beginPath()
+  ctx.arc(x + offsetX, y + offsetY, radius, 0, 6.2831)
+  ctx.fillStyle = 'rgba(0, 0, 0, 0.1)'
+  ctx.fill()
+  ctx.closePath()
+}
 
 function drawBall (x, y, radius, color) {
   ctx.beginPath()
   ctx.arc(x, y, radius, 0, 6.2831)
-  ctx.fillStyle = color
+
+  if (shading) {
+    const offsetX = x + radius * lightAngle[0]
+    const offsetY = y + radius * lightAngle[1]
+    const gradient = ctx.createRadialGradient(offsetX, offsetY, 0, offsetX, offsetY, radius * 1.5)
+    gradient.addColorStop(1, shadeColor(color, -0.3))
+    gradient.addColorStop(0.2, shadeColor(color, 0.4))
+    gradient.addColorStop(0, shadeColor(color, 0.5))
+    ctx.fillStyle = gradient
+  } else {
+    ctx.fillStyle = color
+  }
+
   ctx.fill()
   ctx.closePath()
 }
 
+function shadeColor (color, factor) {
+  // convert rgb string to array: "rgb(11,123,1)" -> [11, 123, 1]
+  const rgb = color.match(/\d+/g).map(Number)
+
+  for (let i = 0; i < 3; i++) {
+    if (factor > 0) {
+      rgb[i] = Math.floor(rgb[i] + (255 - rgb[i]) * factor)
+    } else {
+      rgb[i] = Math.floor(rgb[i] + rgb[i] * factor)
+    }
+  }
+
+  return `rgb(${rgb[0]}, ${rgb[1]}, ${rgb[2]})`
+}
+
 export function drawLine (xFrom, yFrom, xTo, yTo) {
   ctx.beginPath() // Start a new path
   ctx.moveTo(xFrom, yFrom) // Move the pen to (30, 50)
@@ -415,7 +523,7 @@ function drawForceField (ff) {
   const y = ff.y
 
   const gradient = ctx.createRadialGradient(x, y, 0, x, y, ff.radius)
-  gradient.addColorStop(0, 'black')
+  gradient.addColorStop(0, 'lightslategrey')
   gradient.addColorStop(1, 'white')
 
   ctx.beginPath()