4 files changed, 44 insertions, 8 deletions
diff --git a/frontend/_shared/math/line2.js b/frontend/_shared/math/line2.js
index a9e72be..8b30c1c 100644
--- a/frontend/_shared/math/line2.js
+++ b/frontend/_shared/math/line2.js
@@ -32,7 +32,8 @@ function line2(pStart, pEnd, pGl, pColor, pMass) {
         length: length2(lDiffVector),
         mass: pMass,
         direction: normalize2(lDiffVector),
-        velocity: vec2(0, 0)
+        velocity: vec2(0, 0),
+        position: vec2()
     };
 }
 
@@ -40,6 +41,13 @@ 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);
diff --git a/frontend/_shared/math/mat4.js b/frontend/_shared/math/mat4.js
index 6ab29e2..d31a20e 100644
--- a/frontend/_shared/math/mat4.js
+++ b/frontend/_shared/math/mat4.js
@@ -40,4 +40,24 @@ function scaleMatrix(m, x, y, z) {
     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/frontend/_shared/math/rectangle.js b/frontend/_shared/math/rectangle.js
index c24fa12..012c460 100644
--- a/frontend/_shared/math/rectangle.js
+++ b/frontend/_shared/math/rectangle.js
@@ -7,19 +7,19 @@ function rectangle(pGl, pData) {
     pGl.bindBuffer(pGl.ARRAY_BUFFER, lBuffer);
 
     var lBufferedData = [
-        0,              0,              lColor.x, lColor.y, lColor.z, lColor.w,
-        0,              pData.height,   lColor.x, lColor.y, lColor.z, lColor.w,
-        pData.width,    pData.height,   lColor.x, lColor.y, lColor.z, lColor.w,
-        pData.width,    pData.height,   lColor.x, lColor.y, lColor.z, lColor.w,
-        pData.width,    0,              lColor.x, lColor.y, lColor.z, lColor.w,
-        0,              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,
+        -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 Math.pow(pData.width * pData.height, 3.0) / 12.0;
+        return (1.0 / 12.0) * pData.mass * (pData.height * pData.height + pData.width * pData.width);
     };
         
     return makeRigidBody2({
diff --git a/frontend/_shared/math/vec2.js b/frontend/_shared/math/vec2.js
index cff38ce..11e71cd 100644
--- a/frontend/_shared/math/vec2.js
+++ b/frontend/_shared/math/vec2.js
@@ -53,4 +53,12 @@ function negate2(v) {
         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