12 files changed, 602 insertions, 0 deletions
diff --git a/_shared/2d/program_common.js b/_shared/2d/program_common.js
new file mode 100644
index 0000000..48d0a6b
--- /dev/null
+++ b/_shared/2d/program_common.js
@@ -0,0 +1,75 @@
+/// <reference path="shader.js" />
+/// <reference path="../math/mat4.js" />
+
+function getContext(pId, pOnRun) {
+    const lCanvas = $(pId).find('canvas'),
+        lPlayButton = $(pId).find('.play_button'),
+        lStopButton = $(pId).find('.stop_button'),
+        lGl = lCanvas[0].getContext('webgl'),
+        lWidth = lCanvas.width(),
+        lHeight = lCanvas.height();
+
+    return {
+        canvas: lCanvas,
+        playButton: lPlayButton,
+        stopButton: lStopButton,
+        gl: lGl,
+        width: lWidth,
+        height: lHeight,
+        perspective: orthographic(0, lWidth, 0, lHeight),
+        load: function() {
+            lPlayButton.empty().append($('<div>').addClass('spin-loader'));
+            return loadOrthographicShader(lGl).then(function(pProgramInfo) {
+                lPlayButton.css('display', 'none');
+                lStopButton.css('display', 'block');
+                return pProgramInfo;
+            });
+        },
+        reset: function() {
+            lPlayButton.css('display', 'block');
+            lPlayButton.empty().text('Play');
+            lStopButton.css('display', 'none');
+            lStopButton.on('click', undefined);
+        }
+    };
+}
+
+function requestUpdateLoop(pFunction, pOnExit) {
+    let lDeltaTimeSeconds = undefined,
+        lLastTimeSeconds = undefined,
+        lIsRunning = true;
+
+    function update(pTimeStamp) {
+        if (!lIsRunning) {
+            if (pOnExit) {
+                pOnExit();
+            }
+            return;
+        }
+
+        pTimeStamp = pTimeStamp / 1000.0; // Convert to seconds
+
+        // Time calculation
+        if (lLastTimeSeconds === undefined) {
+            lLastTimeSeconds = pTimeStamp;
+            lDeltaTimeSeconds = 0;
+        } else {
+            lDeltaTimeSeconds = pTimeStamp - lLastTimeSeconds;
+            lLastTimeSeconds = pTimeStamp;
+        }
+
+        while (lDeltaTimeSeconds > 0) {
+            pFunction(lDeltaTimeSeconds);
+            lDeltaTimeSeconds -= 0.16;
+        }
+        requestAnimationFrame(update);
+    }
+
+    requestAnimationFrame(update);
+
+    function lExit() {
+        lIsRunning = false;
+    }
+
+    return lExit;
+}
+\ No newline at end of file
diff --git a/_shared/2d/shader.js b/_shared/2d/shader.js
new file mode 100644
index 0000000..7e85a9e
--- /dev/null
+++ b/_shared/2d/shader.js
@@ -0,0 +1,76 @@
+function loadShader(pGl, pShaderType, pShaderSource) {
+    const lShader = pGl.createShader(pShaderType);
+    pGl.shaderSource(lShader, pShaderSource);
+    pGl.compileShader(lShader);
+    if (!pGl.getShaderParameter(lShader, pGl.COMPILE_STATUS)) {
+      alert('An error occurred compiling the shaders: ' + pGl.getShaderInfoLog(lShader));
+      pGl.deleteShader(lShader);
+      return null;
+    }
+  
+    return lShader;
+}
+
+function loadOrthographicShader(pGl) {
+    var lVertex, lFragment;
+
+    function lLoadShaders() {
+        const lVertexShader = loadShader(pGl, pGl.VERTEX_SHADER, lVertex);
+        const lFragmentShader = loadShader(pGl, pGl.FRAGMENT_SHADER, lFragment);
+
+        const lShaderProgram = pGl.createProgram();
+        pGl.attachShader(lShaderProgram, lVertexShader);
+        pGl.attachShader(lShaderProgram, lFragmentShader);
+        pGl.linkProgram(lShaderProgram);
+
+        if (!pGl.getProgramParameter(lShaderProgram, pGl.LINK_STATUS)) {
+            alert('Unable to initialize the shader program: ' + pGl.getProgramInfoLog(lShaderProgram));
+            return null;
+        }
+
+        var lRetval = {
+            program: lShaderProgram,
+            attributeLocations: {
+                position: pGl.getAttribLocation(lShaderProgram, 'position'),
+                color: pGl.getAttribLocation(lShaderProgram, 'color')
+            },
+            uniformLocations: {
+                projection: pGl.getUniformLocation(lShaderProgram, 'projection'),
+                model: pGl.getUniformLocation(lShaderProgram, 'model')
+            }
+        };
+
+        lRetval.renderShape = function(pShape) {
+            pGl.uniformMatrix4fv(lRetval.uniformLocations.model, false, pShape.model);
+            pGl.bindBuffer(pGl.ARRAY_BUFFER, pShape.buffer);
+            {
+                pGl.enableVertexAttribArray(lRetval.attributeLocations.position);
+                pGl.vertexAttribPointer(lRetval.attributeLocations.position, 2, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, 0);
+
+                pGl.enableVertexAttribArray(lRetval.attributeLocations.color);
+                pGl.vertexAttribPointer(lRetval.attributeLocations.color, 4, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, BYTES_PER_FLOAT * 2);
+            }
+
+            pGl.drawArrays(pGl.TRIANGLES, 0, pShape.vertexCount);
+        }
+
+        return lRetval;
+    }
+
+    return fetch('/_shared/2d/shaders/orthographic.vert').then(function(pResponse) {
+        if (pResponse.status === 200) {
+            return pResponse.text().then(function(pShader) {
+                lVertex = pShader;
+
+                return fetch('/_shared/2d/shaders/orthographic.frag').then(function(pResponse) {
+                    if (pResponse.status === 200) {
+                        return pResponse.text().then(function(pShader) {
+                            lFragment = pShader;
+                            return lLoadShaders();
+                        });
+                    }
+                });
+            });
+        }
+    });
+}
+\ No newline at end of file
diff --git a/_shared/2d/shaders/orthographic.frag b/_shared/2d/shaders/orthographic.frag
new file mode 100644
index 0000000..84b6b2e
--- /dev/null
+++ b/_shared/2d/shaders/orthographic.frag
@@ -0,0 +1,5 @@
+varying lowp vec4 VertexColor;
+
+void main() {
+    gl_FragColor = VertexColor;
+}
+\ No newline at end of file
diff --git a/_shared/2d/shaders/orthographic.vert b/_shared/2d/shaders/orthographic.vert
new file mode 100644
index 0000000..0356f9c
--- /dev/null
+++ b/_shared/2d/shaders/orthographic.vert
@@ -0,0 +1,13 @@
+attribute vec2 position;
+attribute vec4 color;
+
+uniform mat4 projection;
+uniform mat4 model;
+
+varying lowp vec4 VertexColor;
+
+void main() {
+    vec4 fragmentPosition = projection * model * vec4(position, 1, 1);
+    gl_Position = fragmentPosition;
+    VertexColor = color;
+}
+\ No newline at end of file
diff --git a/_shared/math/circle.js b/_shared/math/circle.js
new file mode 100644
index 0000000..ba33021
--- /dev/null
+++ b/_shared/math/circle.js
@@ -0,0 +1,112 @@
+/// <reference path="mat4.js" />
+/// <reference path="vec2.js" />
+
+const BYTES_PER_FLOAT = 4;
+
+/**
+ * Initializes a new circle object for the WebGL context.
+ * 
+ * @param {WebGLRenderingContext} pGl 
+ * @param {number} pRadius 
+ * @param {number} pSegments 
+ * @param {Array<Vector4>} pColorList 
+ * @param {vec2} pInitialPosition 
+ * @param {number} pMass 
+ */
+function circle(pGl, pRadius, pSegments, pColorList, pInitialPosition, pMass) {
+    const lBuffer = pGl.createBuffer();
+
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, lBuffer);
+
+    var lBufferedData = [];
+    vertexCount = 0;
+
+    const lAngleIncrements = (360.0 / pSegments) * (Math.PI / 180.0);
+    for (let lSegIdx = 0; lSegIdx < pSegments; lSegIdx++) {
+        const lAngle = lAngleIncrements * lSegIdx,
+            lNextAngle = lAngleIncrements * (lSegIdx + 1),
+            lColorIndex = Math.floor(pColorList.length * (lSegIdx / pSegments)),
+            lColor = pColorList[lColorIndex]; // TODO: Calculate which one to use
+
+        lBufferedData = lBufferedData.concat([
+            0,                              0,                              lColor.x, lColor.y, lColor.z, lColor.w,
+            pRadius * Math.sin(lAngle),     pRadius * Math.cos(lAngle),     lColor.x, lColor.y, lColor.z, lColor.w,
+            pRadius * Math.sin(lNextAngle), pRadius * Math.cos(lNextAngle), lColor.x, lColor.y, lColor.z, lColor.w
+        ]);
+
+        vertexCount += 3;
+    }
+
+    pGl.bufferData(pGl.ARRAY_BUFFER, new Float32Array(lBufferedData), pGl.STATIC_DRAW)
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, undefined);
+
+    return { 
+        buffer: lBuffer, 
+        vertexCount: vertexCount,
+        prevPos: vec2(),
+        position: pInitialPosition || vec2(),
+        prevVelocity: vec2(),
+        velocity: vec2(),
+        force: vec2(),
+        torque: 0,
+        mass: pMass === undefined ? 1 : pMass,
+        rotationVelocity: 0,
+        rotationRadians: 0,
+        model: translateMatrix(mat4(), pInitialPosition ? pInitialPosition.x : 0, pInitialPosition ? pInitialPosition.y : 0, 0),
+        radius: pRadius
+    };
+}
+
+function renderCircle(pGl, pProgramInfo, pCircle) {
+    pGl.uniformMatrix4fv(pProgramInfo.uniformLocations.model, false, pCircle.model);
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, pCircle.buffer);
+    {
+        pGl.enableVertexAttribArray(pProgramInfo.attributeLocations.position);
+        pGl.vertexAttribPointer(pProgramInfo.attributeLocations.position, 2, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, 0);
+
+        pGl.enableVertexAttribArray(pProgramInfo.attributeLocations.color);
+        pGl.vertexAttribPointer(pProgramInfo.attributeLocations.color, 4, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, BYTES_PER_FLOAT * 2);
+    }
+
+    pGl.drawArrays(pGl.TRIANGLE_STRIP, 0, pCircle.vertexCount);
+}
+
+function getCircleMomentOfInertia(pCircle) {
+    return (Math.PI * Math.pow(pCircle.radius, 4)) / 4;
+}
+
+function doCirclesIntersect(pFirst, pSecond) {
+    const lDistanceBetween = Math.pow(pFirst.position.x - pSecond.position.x, 2) 
+        + Math.pow(pFirst.position.y - pSecond.position.y, 2)
+    return lDistanceBetween <= Math.pow(pFirst.radius + pSecond.radius, 2);
+}
+
+/**
+ * Returns intersection information about the intersecting circles.
+ * 
+ * Warning! Only use this if doCirclesIntersect returned true for these circles.
+ * 
+ * @param {circle} pFirst 
+ * @param {circle} pSecond 
+ */
+function getIntersectionDataForCircles(pFirst, pSecond) {
+    // The collision normal is simply the difference between the two current positions
+    const lCollisionNormal = normalize2(subVec2(pFirst.position, pSecond.position));
+    const lCollisionPoint = vec2(
+        ((pFirst.position.x * pSecond.radius) + (pSecond.position.x * pFirst.radius)) / (pFirst.radius + pSecond.radius),
+        ((pFirst.position.y * pSecond.radius) + (pSecond.position.y * pFirst.radius))  / (pFirst.radius + pSecond.radius)
+    );
+
+    return {
+        relativeVelocity:   subVec2(pFirst.velocity, pSecond.velocity),
+        collisionNormal:    lCollisionNormal,
+        //firstPointOfApplication: addVec2(scaleVec2(normalize2(pFirst.velocity), pFirst.radius), pFirst.position),
+        //secondPointOfApplication: addVec2(scaleVec2(normalize2(pSecond.velocity), pSecond.radius), pSecond.position)
+        firstPointOfApplication: subVec2(lCollisionPoint, pFirst.position),
+        secondPointOfApplication: subVec2(lCollisionPoint, pSecond.position)
+    }
+}
+
+function freeCircle(pGl, pCircle) {
+    pGl.deleteBuffer(pCircle.buffer);
+}
+\ No newline at end of file
diff --git a/_shared/math/collision.js b/_shared/math/collision.js
new file mode 100644
index 0000000..8e4be7d
--- /dev/null
+++ b/_shared/math/collision.js
@@ -0,0 +1,26 @@
+/// <reference path="vec2.js" />
+/// <reference path="line2.js" />
+/// <reference path="circle.js" />
+/// <reference path="mat4.js" />
+/// <reference path="point2.js" />
+
+/**
+ * 
+ * @param {circle} pCircle 
+ * @param {line2} pLine 
+ */
+function lineCircleCollision2(pCircle, pLine) {
+    return distanceFromPoint2ToLine2(pCircle.position, pLine) <= pCircle.radius;
+}
+
+function getLineCircleCollison2Data(pCircle, pLine) {
+    const lCollisionNormal = pLine.normal,
+        lCollisionPoint = addVec2(pCircle.position, scaleVec2(negate2(lCollisionNormal), pCircle.radius));
+        
+    return {
+        relativeVelocity:           subVec2(pCircle.velocity, pLine.velocity),
+        collisionNormal:            lCollisionNormal,
+        firstPointOfApplication:    subVec2(lCollisionPoint, pCircle.position),
+        secondPointOfApplication:   subVec2(lCollisionPoint, pLine.start)
+    }
+}
+\ No newline at end of file
diff --git a/_shared/math/line2.js b/_shared/math/line2.js
new file mode 100644
index 0000000..8b30c1c
--- /dev/null
+++ b/_shared/math/line2.js
@@ -0,0 +1,63 @@
+/// <reference path="vec2.js" />
+/// <reference path="mat4.js" />
+
+/**
+ * Creates a new line object
+ * @param {vec2} pStart 
+ * @param {vec2} pEnd 
+ * @param {WebGLRenderingContext} pGl
+ */
+function line2(pStart, pEnd, pGl, pColor, pMass) {
+    const lDiffVector = subVec2(pEnd, pStart);
+
+    const lBuffer = pGl.createBuffer();
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, lBuffer);
+
+    var lBufferedData = [
+        pStart.x, pStart.y, pColor.x, pColor.y, pColor.z, pColor.w,
+        pEnd.x, pEnd.y, pColor.x, pColor.y, pColor.z, pColor.w
+    ];
+
+    pGl.bufferData(pGl.ARRAY_BUFFER, new Float32Array(lBufferedData), pGl.STATIC_DRAW)
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, undefined);
+
+    var lSlope = (pEnd.y - pStart.y) / (pEnd.x - pStart.x);
+
+    return {
+        buffer: lBuffer,
+        start: pStart,
+        end: pEnd,
+        slope: lSlope,
+        normal: normalize2(getPerp2(lDiffVector)),
+        length: length2(lDiffVector),
+        mass: pMass,
+        direction: normalize2(lDiffVector),
+        velocity: vec2(0, 0),
+        position: vec2()
+    };
+}
+
+function getLine2MomentOfInertia(pLine) {
+    return (1.0 / 12.0) * pLine.mass * Math.pow(pLine.length, 2);
+}
+
+function getLine2MidPoint(pLine) {
+    return {
+        x: (pLine.end.x + pLine.start.x) / 2.0,
+        y: (pLine.end.y + pLine.start.y) / 2.0
+    }
+}
+
+function renderLine2(pGl, pProgramInfo, pLine) {
+    pGl.uniformMatrix4fv(pProgramInfo.uniformLocations.model, false, mat4()); // Model on a line is always default matrix
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, pLine.buffer);
+    {
+        pGl.enableVertexAttribArray(pProgramInfo.attributeLocations.position);
+        pGl.vertexAttribPointer(pProgramInfo.attributeLocations.position, 2, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, 0);
+
+        pGl.enableVertexAttribArray(pProgramInfo.attributeLocations.color);
+        pGl.vertexAttribPointer(pProgramInfo.attributeLocations.color, 4, pGl.FLOAT, false, BYTES_PER_FLOAT * 6, BYTES_PER_FLOAT * 2);
+    }
+
+    pGl.drawArrays(pGl.LINES, 0, 2);
+}
+\ No newline at end of file
diff --git a/_shared/math/mat4.js b/_shared/math/mat4.js
new file mode 100644
index 0000000..d31a20e
--- /dev/null
+++ b/_shared/math/mat4.js
@@ -0,0 +1,63 @@
+function mat4() {
+    return [
+        1, 0, 0, 0,
+        0, 1, 0, 0,
+        0, 0, 1, 0,
+        0, 0, 0, 1
+    ]
+}
+
+function orthographic(pLeft, pRight, pBottom, pTop) {
+    const lResult = mat4();
+    lResult[0] = 2.0 / (pRight - pLeft);
+    lResult[5] = 2.0 / (pTop - pBottom);
+    lResult[10] = 1.0;
+    lResult[12] = -(pRight + pLeft) / (pRight - pLeft);
+    lResult[13] = -(pTop + pBottom) / (pTop - pBottom);
+    return lResult;
+}
+
+function translateMatrix(m, x, y, z) {
+    m = [...m];
+    m[12] += x;
+    m[13] += y;
+    m[14] += z;
+    return m;
+}
+
+function rotateMatrix2d(m, angle) {
+    m = [...m];
+    m[0] = Math.cos(angle);
+    m[1] = -Math.sin(angle);
+    m[4] = Math.sin(angle);
+    m[5] = Math.cos(angle);
+    return m;
+}
+
+function scaleMatrix(m, x, y, z) {
+    m = [...m];
+    m[0] = m[0] * x;
+    m[5] = m[5] * y;
+    m[10] = m[10] * z;
+    return m;
+}
+
+function multMat4ByVec2(matrix, vec) {
+    var lInnerVec = {...vec};
+    lInnerVec.z = 0.0;
+    lInnerVec.w = 1.0;
+
+    return {
+        x: lInnerVec.x * matrix[0] + lInnerVec.y * matrix[4] + lInnerVec.z * matrix[8] + lInnerVec.w * matrix[12],
+        y: lInnerVec.x * matrix[1] + lInnerVec.y * matrix[5] + lInnerVec.z * matrix[9] + lInnerVec.w * matrix[13]
+    };
+}
+
+function multMat4ByVec4(matrix, vec) {
+    return {
+        x: vec.x * matrix[0] + vec.y * matrix[4] + vec.z * matrix[8] + vec.w * matrix[12],
+        y: vec.x * matrix[1] + vec.y * matrix[5] + vec.z * matrix[9] + vec.w * matrix[13],
+        z: vec.x * matrix[2] + vec.y * matrix[6] + vec.z * matrix[10] + vec.w * matrix[14],
+        w: vec.x * matrix[3] + vec.y * matrix[7] + vec.z * matrix[11] + vec.w * matrix[15]
+    };
+}
+\ No newline at end of file
diff --git a/_shared/math/point2.js b/_shared/math/point2.js
new file mode 100644
index 0000000..eeacd91
--- /dev/null
+++ b/_shared/math/point2.js
@@ -0,0 +1,16 @@
+function point2(x = 0, y = 0) {
+    return { x: x, y: y };
+}
+
+function distanceFromPoint2ToLine2(pPoint, pLine) {
+    // Check out this wikapedia article for more information:
+    // https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line
+    var x0 = pPoint.x,
+        y0 = pPoint.y,
+        x1 = pLine.start.x,
+        y1 = pLine.start.y,
+        x2 = pLine.end.x,
+        y2 = pLine.end.y;
+
+    return Math.abs((x2 - x1) * (y1 - y0) - (x1 - x0) * (y2 - y1)) / Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2));
+}
+\ No newline at end of file
diff --git a/_shared/math/rectangle.js b/_shared/math/rectangle.js
new file mode 100644
index 0000000..012c460
--- /dev/null
+++ b/_shared/math/rectangle.js
@@ -0,0 +1,32 @@
+/// <reference path="rigidbody2.js" />
+
+function rectangle(pGl, pData) {
+    var lBuffer = pGl.createBuffer(),
+        lColor = pData.color || { x: 1, y: 0, z: 0, w: 1 };
+
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, lBuffer);
+
+    var lBufferedData = [
+        -pData.width / 2.0, -pData.height / 2.0,    lColor.x, lColor.y, lColor.z, lColor.w,
+        -pData.width / 2.0, pData.height / 2.0,     lColor.x, lColor.y, lColor.z, lColor.w,
+        pData.width / 2.0,  pData.height / 2.0,     lColor.x, lColor.y, lColor.z, lColor.w,
+        pData.width / 2.0,  pData.height /2.0,      lColor.x, lColor.y, lColor.z, lColor.w,
+        pData.width / 2.0,  -pData.height / 2.0,    lColor.x, lColor.y, lColor.z, lColor.w,
+        -pData.width / 2.0, -pData.height / 2.0,    lColor.x, lColor.y, lColor.z, lColor.w
+    ];
+
+    pGl.bufferData(pGl.ARRAY_BUFFER, new Float32Array(lBufferedData), pGl.STATIC_DRAW)
+    pGl.bindBuffer(pGl.ARRAY_BUFFER, undefined);
+
+    pData.getMomentOfInertia = function() {
+        return (1.0 / 12.0) * pData.mass * (pData.height * pData.height + pData.width * pData.width);
+    };
+        
+    return makeRigidBody2({
+        vertexCount:    6,
+        buffer:         lBuffer, 
+        width:          pData.width,
+        height:         pData.height,
+        model:          translateMatrix(mat4(), pData.position ? pData.position.x : 0, pData.position ? pData.position.y : 0, 0),
+    }, pData);
+}
+\ No newline at end of file
diff --git a/_shared/math/rigidbody2.js b/_shared/math/rigidbody2.js
new file mode 100644
index 0000000..0b18d0c
--- /dev/null
+++ b/_shared/math/rigidbody2.js
@@ -0,0 +1,57 @@
+/// <reference path="vec2.js" />
+/// <reference path="mat4.js" />
+/// <reference path="circle.js" />
+/// <reference path="line2.js" />
+/// <reference path="collision.js" />
+
+const GRAVITY = 9.8;
+const BYTES_PER_FLOAT = 4;
+
+/**
+ * 
+ * @param {Shape} pObject a 2D shape like a circle, rectangle, or line
+ * @param {Object} pData initial data for the rigidboy
+ */
+function makeRigidBody2(pObject, pData) {
+    pObject.velocity            = vec2();
+    pObject.prevVelocity        = pObject.velocity;
+    pObject.position            = pData.position || vec2();
+    pObject.prevPosition        = pObject.position;
+    pObject.force               = vec2();
+    pObject.rotationVelocity    = 0;
+    pObject.rotationRadians     = 0;
+    pObject.torque              = 0;
+    pObject.mass                = pData.mass !== undefined ? pData.mass : 1.0;
+    pObject.getMomentOfInertia  = pData.getMomentOfInertia;
+
+    return pObject;
+}
+
+function updateRigidBody2(pRigidbody, pDeltaTimeSeconds) {
+    applyForceRigidbody2(pRigidbody, vec2(0, -1.0 * (pRigidbody.mass * GRAVITY)));
+    const lCurrentAcceleration = scaleVec2(pRigidbody.force, 1.0 / pRigidbody.mass);
+    pRigidbody.prevVelocity = pRigidbody.velocity;
+    pRigidbody.velocity = addVec2(pRigidbody.velocity, scaleVec2(lCurrentAcceleration, pDeltaTimeSeconds));
+    pRigidbody.prevPos = { ...pRigidbody.position };
+    pRigidbody.position = addVec2(pRigidbody.position, scaleVec2(pRigidbody.velocity, pDeltaTimeSeconds));
+    pRigidbody.force = vec2();
+
+    const lMomentOfInertia =  pRigidbody.getMomentOfInertia(pRigidbody);
+    const lAngularAcceleration = pRigidbody.torque / lMomentOfInertia;
+    pRigidbody.rotationVelocity += lAngularAcceleration * pDeltaTimeSeconds;
+    pRigidbody.rotationRadians += pRigidbody.rotationVelocity * pDeltaTimeSeconds;
+    pRigidbody.torque = 0;
+
+    pRigidbody.model = rotateMatrix2d(translateMatrix(mat4(), pRigidbody.position.x, pRigidbody.position.y, 0), pRigidbody.rotationRadians);
+}
+
+function applyForceRigidbody2(pRigidbody, pForceVector, pPointOfApplication) {
+    if (pPointOfApplication !== undefined) {
+        const lOriginToPointOfApp = subVec2(vec2(), pPointOfApplication),
+            lPerpVec = vec2(-lOriginToPointOfApp.y, lOriginToPointOfApp.x);
+
+            pRigidbody.torque += TORQUE_MULTIPLIER * dot2(lPerpVec, pForceVector);
+    }
+
+    pRigidbody.force = addVec2(pRigidbody.force, pForceVector);
+}
diff --git a/_shared/math/vec2.js b/_shared/math/vec2.js
new file mode 100644
index 0000000..11e71cd
--- /dev/null
+++ b/_shared/math/vec2.js
@@ -0,0 +1,64 @@
+function vec2(x = 0, y = 0) {
+    return { x: x, y: y};
+}
+
+function addVec2(v1, v2) {
+    return {
+        x: v1.x + v2.x,
+        y: v1.y + v2.y
+    };
+}
+
+function subVec2(v1, v2) {
+    return {
+        x: v1.x - v2.x,
+        y: v1.y - v2.y
+    };
+}
+
+function scaleVec2(v, s) {
+    return {
+        x: v.x * s,
+        y: v.y * s
+    };
+}
+
+function dot2(v1, v2) {
+    return v1.x * v2.x + v1.y * v2.y;
+}
+
+function length2(v) {
+    return Math.sqrt(v.x * v.x + v.y * v.y);
+}
+
+function normalize2(v) {
+    const lLength = length2(v);
+    const lInverseLength = lLength === 0 ? 1.0 : 1.0 / length2(v);
+    return { x: v.x * lInverseLength, y: v.y * lInverseLength };
+}
+
+function vec2str(v) {
+    return `(${v.x.toFixed(2)}, ${v.y.toFixed(2)})`;
+}
+
+function getPerp2(v) {
+    return {
+        x: -v.y,
+        y: v.x
+    };
+}
+
+function negate2(v) {
+    return {
+        x: -v.x,
+        y: -v.y
+    };
+}
+
+// Algorithm plucked from: https://matthew-brett.github.io/teaching/rotation_2d.html
+function rotateAboutOrigin2(v, angle) {
+    return {
+        x: v.x * Math.cos(angle) - v.y * Math.sin(angle),
+        y: v.x * Math.sin(angle) + v.y * Math.cos(angle),
+    };
+}
+\ No newline at end of file