tylerneylon · March 17, 2016 20:49
diff --git a/animated_svg.html b/animated_svg.html
 <!DOCTYPE HTML>
 <html>
  <body>
    <svg width="600" height="600" vertion="1.1"
    id="svg" xmlns="http://www.w3.org/2000/svg">

      <defs>
        <clipPath id="angleClip">
          <polygon id="atriangle" />
        </clipPath>
      </defs>
    </svg>
    <script>

      var radius = 91
      var cx     = 100
      var cy     = 100

      function xOfRads(a) {
        return cx + radius * Math.cos(a)
      }

      function yOfRads(a) {
        return cy - radius * Math.sin(a)
      }

      function ptOfAngleInRadians(a) {
        return xOfRads(a) + ' ' + yOfRads(a)
      }

      // This expects an array of radians as input.
      // The output is formatted for use as a 'points' value in a polygon elt.
      function polyPoints(arr) {
        var s = []
        for (var i = 0; i < arr.length; i++) {
          s.push(ptOfAngleInRadians(arr[i]))
        }
        return s.join(', ')
      }

      function dist(x1, y1, x2, y2) {
        var d1 = x1 - x2
        var d2 = y1 - y2
        return Math.sqrt(d1 * d1 + d2 * d2)
      }

      function addAttributes(elt, attr) {
        for (var key in attr) {
          elt.setAttribute(key, attr[key])
        }
        return elt
      }

      function add(eltName, attr) {
        var elt = document.createElementNS(svgNS, eltName)
        svg.appendChild(elt)
        if (attr) addAttributes(elt, attr)
        return elt
      }

      function addDot() {
        var dotStyle = {stroke: 'transparent', fill: '#444', r: 3}
        return add('circle', dotStyle)
      }


      // Begin instance-specific code.

      var svg = document.getElementById('svg')
      var svgNS = svg.namespaceURI

      var lightStyle = {stroke: '#ddd', fill: 'transparent', 'stroke-width': 3}
      var darkStyle = {stroke: '#666', fill: 'transparent', 'stroke-width': 3}

      // Circle.
      var circle = add('circle', lightStyle)
      addAttributes(circle, {cx: cx, cy: cy, r: radius, stroke: '#f0f0f0'})

      // Set up some angles we'll use in a few places.
      var rads = [1.0, 2.3, 4.6]
      var pi   = Math.PI

      // Add the triangle; we'll use a function to position it, so just add the
      // elements for now.
      var triSides  = []
      var triPoints = []
      var colors = ['#D98162', '#4586A5', '#CC6969']
      var shadedArea = add('polygon', {stroke: 'transparent', fill: '#e2e2e2'})
      for (var i = 0; i < 3; i++) {
        triSides[i]  = add('line', darkStyle)
        addAttributes(triSides[i], {stroke: colors[i]})
      }
      for (var i = 0; i < 3; i++) triPoints[i] = addDot()

      // Add side length indicators and labels for them.
      var sideLens = []
      var sideLabels = []
      var labels = ['a', 'b', 'c']
      var labelStyle = {'font-family': 'Charter',
                        'font-size': 19,
                        'font-style': 'italic'}
      for (var i = 0; i < 3; i++) {
        sideLens[i] = add('line', darkStyle)
        addAttributes(sideLens[i], {stroke: colors[i]})

        sideLabels[i] = add('text', labelStyle)
        sideLabels[i].innerHTML = labels[i]
      }

      var xOfLabels = 203
      var xOfValues = xOfLabels + 17

      // Add labels for abc/4 and area.
      var eqnLabels = []
      var eqnLabelStrings = ['abc/4', 'area']
      var eqnValues = []
      var valueStyle = {'font-family': 'Courier New', 'font-size': 19}
      for (var i = 0; i < 2; i++) {
        eqnLabels[i] = add('text', labelStyle)
        eqnLabels[i].innerHTML = eqnLabelStrings[i]
        addAttributes(eqnLabels[i], {x: xOfLabels, y: 117 + 50 * i})

        eqnValues[i] = add('text', valueStyle)
        addAttributes(eqnValues[i], {x: xOfValues, y: 140 + 50 * i})
        addAttributes(eqnValues[i], {fill: '#999'})
      }

      var a, b, c  // Mathematical side lengths (for a unit circle).

      function updateABC() {
        var x = [], y = []
        var lens = []
        for (var i = 0; i < 3; i++) {
          x[i] = Math.cos(rads[i])
          y[i] = Math.sin(rads[i])
        }
        for (var i = 0; i < 3; i++) {
          var dx = x[i] - x[(i + 1) % 3]
          var dy = y[i] - y[(i + 1) % 3]
          lens[i] = Math.sqrt(dx * dx + dy * dy)
        }
        a = lens[0], b = lens[1], c = lens[2]
      }

      function abcOverFour() {
        return a * b * c / 4
      }

      function heronsFormula() {
        var s = (a + b + c) / 2
        return Math.sqrt(s * (s - a) * (s - b) * (s - c))
      }

      function moveTriangle(rads) {
        for (var i = 0; i < 3; i++) {
          var r1 = rads[i]
          var r2 = rads[(i + 1) % 3]
          var x1 = xOfRads(r1), y1 = yOfRads(r1)
          var x2 = xOfRads(r2), y2 = yOfRads(r2)
          addAttributes(triSides[i], {x1: x1, y1: y1, x2: x2, y2: y2,
                                      'stroke-width': 4})
          addAttributes(triPoints[i], {cx: xOfRads(r1), cy: yOfRads(r1)})
          var dx = x1 - x2, dy = y1 - y2
          var len = Math.sqrt(dx * dx + dy * dy) / (2 * radius) * 70
          var y = 23 + i * 28
          addAttributes(sideLens[i], {x1: xOfValues, y1: y,
                                      x2: xOfValues + len, y2: y})
          addAttributes(sideLabels[i], {x: xOfLabels, y: y + 5})
        }
        addAttributes(shadedArea, {points: polyPoints(rads)})

        // Update the area-oriented values.
        updateABC()
        var area0 = abcOverFour()
        eqnValues[0].innerHTML = area0.toFixed(3) + '..'
        var area1 = heronsFormula()
        eqnValues[1].innerHTML = area1.toFixed(3) + '..'
      }

      moveTriangle(rads)


      // Animation code.

      var lastTimestamp = null
      var baseRadiansPerMilliSec = 0.0007

      function step(timestamp) {
        if (lastTimestamp !== null) {
          var milliSecDelta = timestamp - lastTimestamp
          var radiansDelta = baseRadiansPerMilliSec * milliSecDelta
          var factors = [1, 2, -1]
          for (var i = 0; i < 3; i++) {
            rads[i] += radiansDelta * factors[i]
          }
          moveTriangle(rads)
        }
        lastTimestamp = timestamp
        window.requestAnimationFrame(step)
      }

      // Initialize the animation.
      window.requestAnimationFrame(step)

    </script>
  </body>
 </html>
	<!DOCTYPE HTML>
	<html>
	<body>
	<svg width="600" height="600" vertion="1.1"
	id="svg" xmlns="http://www.w3.org/2000/svg">

	<defs>
	<clipPath id="angleClip">
	<polygon id="atriangle" />
	</clipPath>
	</defs>
	</svg>
	<script>

	var radius = 91
	var cx = 100
	var cy = 100

	function xOfRads(a) {
	return cx + radius * Math.cos(a)
	}

	function yOfRads(a) {
	return cy - radius * Math.sin(a)
	}

	function ptOfAngleInRadians(a) {
	return xOfRads(a) + ' ' + yOfRads(a)
	}

	// This expects an array of radians as input.
	// The output is formatted for use as a 'points' value in a polygon elt.
	function polyPoints(arr) {
	var s = []
	for (var i = 0; i < arr.length; i++) {
	s.push(ptOfAngleInRadians(arr[i]))
	}
	return s.join(', ')
	}

	function dist(x1, y1, x2, y2) {
	var d1 = x1 - x2
	var d2 = y1 - y2
	return Math.sqrt(d1 * d1 + d2 * d2)
	}

	function addAttributes(elt, attr) {
	for (var key in attr) {
	elt.setAttribute(key, attr[key])
	}
	return elt
	}

	function add(eltName, attr) {
	var elt = document.createElementNS(svgNS, eltName)
	svg.appendChild(elt)
	if (attr) addAttributes(elt, attr)
	return elt
	}

	function addDot() {
	var dotStyle = {stroke: 'transparent', fill: '#444', r: 3}
	return add('circle', dotStyle)
	}


	// Begin instance-specific code.

	var svg = document.getElementById('svg')
	var svgNS = svg.namespaceURI

	var lightStyle = {stroke: '#ddd', fill: 'transparent', 'stroke-width': 3}
	var darkStyle = {stroke: '#666', fill: 'transparent', 'stroke-width': 3}

	// Circle.
	var circle = add('circle', lightStyle)
	addAttributes(circle, {cx: cx, cy: cy, r: radius, stroke: '#f0f0f0'})

	// Set up some angles we'll use in a few places.
	var rads = [1.0, 2.3, 4.6]
	var pi = Math.PI

	// Add the triangle; we'll use a function to position it, so just add the
	// elements for now.
	var triSides = []
	var triPoints = []
	var colors = ['#D98162', '#4586A5', '#CC6969']
	var shadedArea = add('polygon', {stroke: 'transparent', fill: '#e2e2e2'})
	for (var i = 0; i < 3; i++) {
	triSides[i] = add('line', darkStyle)
	addAttributes(triSides[i], {stroke: colors[i]})
	}
	for (var i = 0; i < 3; i++) triPoints[i] = addDot()

	// Add side length indicators and labels for them.
	var sideLens = []
	var sideLabels = []
	var labels = ['a', 'b', 'c']
	var labelStyle = {'font-family': 'Charter',
	'font-size': 19,
	'font-style': 'italic'}
	for (var i = 0; i < 3; i++) {
	sideLens[i] = add('line', darkStyle)
	addAttributes(sideLens[i], {stroke: colors[i]})

	sideLabels[i] = add('text', labelStyle)
	sideLabels[i].innerHTML = labels[i]
	}

	var xOfLabels = 203
	var xOfValues = xOfLabels + 17

	// Add labels for abc/4 and area.
	var eqnLabels = []
	var eqnLabelStrings = ['abc/4', 'area']
	var eqnValues = []
	var valueStyle = {'font-family': 'Courier New', 'font-size': 19}
	for (var i = 0; i < 2; i++) {
	eqnLabels[i] = add('text', labelStyle)
	eqnLabels[i].innerHTML = eqnLabelStrings[i]
	addAttributes(eqnLabels[i], {x: xOfLabels, y: 117 + 50 * i})

	eqnValues[i] = add('text', valueStyle)
	addAttributes(eqnValues[i], {x: xOfValues, y: 140 + 50 * i})
	addAttributes(eqnValues[i], {fill: '#999'})
	}

	var a, b, c // Mathematical side lengths (for a unit circle).

	function updateABC() {
	var x = [], y = []
	var lens = []
	for (var i = 0; i < 3; i++) {
	x[i] = Math.cos(rads[i])
	y[i] = Math.sin(rads[i])
	}
	for (var i = 0; i < 3; i++) {
	var dx = x[i] - x[(i + 1) % 3]
	var dy = y[i] - y[(i + 1) % 3]
	lens[i] = Math.sqrt(dx * dx + dy * dy)
	}
	a = lens[0], b = lens[1], c = lens[2]
	}

	function abcOverFour() {
	return a * b * c / 4
	}

	function heronsFormula() {
	var s = (a + b + c) / 2
	return Math.sqrt(s * (s - a) * (s - b) * (s - c))
	}

	function moveTriangle(rads) {
	for (var i = 0; i < 3; i++) {
	var r1 = rads[i]
	var r2 = rads[(i + 1) % 3]
	var x1 = xOfRads(r1), y1 = yOfRads(r1)
	var x2 = xOfRads(r2), y2 = yOfRads(r2)
	addAttributes(triSides[i], {x1: x1, y1: y1, x2: x2, y2: y2,
	'stroke-width': 4})
	addAttributes(triPoints[i], {cx: xOfRads(r1), cy: yOfRads(r1)})
	var dx = x1 - x2, dy = y1 - y2
	var len = Math.sqrt(dx * dx + dy * dy) / (2 * radius) * 70
	var y = 23 + i * 28
	addAttributes(sideLens[i], {x1: xOfValues, y1: y,
	x2: xOfValues + len, y2: y})
	addAttributes(sideLabels[i], {x: xOfLabels, y: y + 5})
	}
	addAttributes(shadedArea, {points: polyPoints(rads)})

	// Update the area-oriented values.
	updateABC()
	var area0 = abcOverFour()
	eqnValues[0].innerHTML = area0.toFixed(3) + '..'
	var area1 = heronsFormula()
	eqnValues[1].innerHTML = area1.toFixed(3) + '..'
	}

	moveTriangle(rads)


	// Animation code.

	var lastTimestamp = null
	var baseRadiansPerMilliSec = 0.0007

	function step(timestamp) {
	if (lastTimestamp !== null) {
	var milliSecDelta = timestamp - lastTimestamp
	var radiansDelta = baseRadiansPerMilliSec * milliSecDelta
	var factors = [1, 2, -1]
	for (var i = 0; i < 3; i++) {
	rads[i] += radiansDelta * factors[i]
	}
	moveTriangle(rads)
	}
	lastTimestamp = timestamp
	window.requestAnimationFrame(step)
	}

	// Initialize the animation.
	window.requestAnimationFrame(step)

	</script>
	</body>
	</html>