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coodoo/a.js

Last active Nov 27, 2020
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function matrixArrayToCssMatrix(array) {
return "matrix3d(" + array.join(',') + ")";
}
function multiplyMatrixAndPoint(matrix, point) {
//Give a simple variable name to each part of the matrix, a column and row number
var c0r0 = matrix[0],
c1r0 = matrix[1],
c2r0 = matrix[2],
c3r0 = matrix[3];
var c0r1 = matrix[4],
c1r1 = matrix[5],
c2r1 = matrix[6],
c3r1 = matrix[7];
var c0r2 = matrix[8],
c1r2 = matrix[9],
c2r2 = matrix[10],
c3r2 = matrix[11];
var c0r3 = matrix[12],
c1r3 = matrix[13],
c2r3 = matrix[14],
c3r3 = matrix[15];
//Now set some simple names for the point
var x = point[0];
var y = point[1];
var z = point[2];
var w = point[3];
//Multiply the point against each part of the 1st column, then add together
var resultX = (x * c0r0) + (y * c0r1) + (z * c0r2) + (w * c0r3);
//Multiply the point against each part of the 2nd column, then add together
var resultY = (x * c1r0) + (y * c1r1) + (z * c1r2) + (w * c1r3);
//Multiply the point against each part of the 3rd column, then add together
var resultZ = (x * c2r0) + (y * c2r1) + (z * c2r2) + (w * c2r3);
//Multiply the point against each part of the 4th column, then add together
var resultW = (x * c3r0) + (y * c3r1) + (z * c3r2) + (w * c3r3);
return [resultX, resultY, resultZ, resultW];
}
// 將 float 轉成 number 避免出現 -1.23-e 這種值
const to = n => Number(n.toFixed(2))
var sin = Math.sin;
var cos = Math.cos;
// cx/y = current x, y 以左上角為準
function rotate(rotation, w, h, cx, cy) {
// degree to radian
var a = rotation * (Math.PI / 180)
//
var rotateZMatrix = [
cos(a), -sin(a), 0, 0,
sin(a), cos(a), 0, 0,
0, 0, 1, 0,
0, 0, 0, 1
];
// 不管中心點位置,一律反推出左上角座標
const diffX = w / 2
const diffY = h / 2
const x = -diffX
const y = -diffY
// 方型左上角距 (0, 0) 的距離,通常直接讀取方型的 (x, y) 就夠
const offsetX = cx
const offsetY = cy
// 然後與 rotation matrix 相乘得到旋轉後位置
const [x1, y1] = multiplyMatrixAndPoint(rotateZMatrix, [x, y, 0, 1])
// 原點不在 (0,0) 時要加上離原點的位移值
const finalX = to(x1 + diffX + offsetX)
const finalY = to(y1 + diffY + offsetY)
console.log('\n\n', { finalX, finalY }, '\t', { x, y, diffX, diffY, w, h })
}
// 測試
console.log(rotate(45, 100, 100, 0, 0))
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