如何反向工程的WebKit的Matrix3D变换(How to reverse-engineer a

我有被旋转的立方体元素，并在3D空间转换。

我想找出只是这个旋转Y部分变换在给定时间。这可能吗？

我有：

var cube = document.getElementById("cube");
var transform = getComputedStyle(cube).webkitTransform;

//the value of transform is:
// matrix3d(-1, 0, 0.00000000000000012246467991473532, 0, 
//           0, 1, 0, 0, 
//          -0.00000000000000012246467991473532, 0, -1, 0, 
//           0, 0, 0, 1)

救命？ :-)

Answer 1:

如果你的对象只被绕Y，然后是，旋转是简单的计算-它是矩阵的元素1,1 ARCCOS或3,3或的阿尔辛- （元素3,1）或ARCSIN元件1， 3。在您的具体的例子，这是约180度。如果旋转是不仅仅是y轴越多，那么你必须开始跟踪先前旋转，它可以让混乱。

你的翻译将只是输出矩阵的底行，0,0,0在这种情况下。

参见例子http://www.inversereality.org/tutorials/graphics%20programming/3dwmatrices.html

Answer 2:

你可以用“新WebKitCSSMatrix”功能检索改造信息。例如：

var matrix = new WebKitCSSMatrix($('#element').css('-webkit-transform'));
var translateZ = matrix.m43;

矩阵的每个部分是在这里说明一下： http://9elements.com/html5demos/matrix3d/可以检索更配合物的属性，如的rotationX，对于数学一塌糊涂3D矩阵：

var rotationX = Math.acos(matrix.a) * (180/Math.PI);
var rotationY = Math.asin(matrix.b) * (180/Math.PI);

Answer 3:

给定的函数确定rotation* ， transform*和scale对于给定的DOM元素跨浏览器 。

如果你想要更多的东西，或者发现数学漏洞，它是在一个讨论math.stackexchange.com

经测试在列出的浏览器http://caniuse.com/transforms3d ：

var reverseEngineerTransform3d = function (domElement, parameterName) {

        parameterName = parameterName.toLowerCase();

        var computedStyle = window.getComputedStyle(domElement),
            matrixStyle = computedStyle.transform || computedStyle.WebkitTransform || computedStyle.MozTransform || computedStyle.msTransform || computedStyle.OTransform;

        if (matrixStyle) {
            matrixStyle = matrixStyle.trim();
        }

        if (matrixStyle === 'none') {
            if (parameterName.indexOf('rotate') === 0) {
                return '0deg';
            } else if (parameterName.indexOf('translate') === 0) {
                return '0px';
            } else if (parameterName === 'scale') {
                return 1;
            } else {
                throw "Unsupported 3D parameter " + parameterName;
            }
        }

        else if (!matrixStyle || matrixStyle.substr(0, 9) !== 'matrix3d(') {
            //return something or die ?????
            throw "Something is wrong with 3D transform style. Probably no style applied at all OR unknown CSS3 vendor OR unknown/unsupported 3D matrix representation string OR CSS3 3D transform is not fully supported in this browser";
        }

        var matrix = window.WebKitCSSMatrix && (new WebKitCSSMatrix(matrixStyle)) ||
                window.MozCSSMatrix && (new MozCSSMatrix(matrixStyle)) ||
                window.MsCSSMatrix && (new MsCSSMatrix(matrixStyle)) ||
                window.OCSSMatrix && (new OCSSMatrix(matrixStyle)) ||
                window.CSSMatrix && (new CSSMatrix(matrixStyle)); // sorry 4 copy-paste my friends

        if (!matrix || isNaN(matrix.a) || isNaN(matrix.b) || isNaN(matrix.c) || isNaN(matrix.m41) || isNaN(matrix.m42) || isNaN(matrix.m43) || isNaN(matrix.m11)) {
            throw "Could not catch CSSMatrix constructor for current browser, OR the constructor has returned a non-standard matrix object (need .a, .b, .c and mXX numerical properties to work)";
        }


        // todo: giving a parameters array (and returning an array) is a good idea, or we could return everything if no parameters given

        switch (parameterName) {

            case 'rotatey':  // in degrees
                return Math.acos(matrix.m11)*180/Math.PI * (matrix.m13 > 0 ? -1 : 1) + 'deg';

            case 'rotatex':  // in degrees
                return Math.asin(matrix.m22)*180/Math.PI + 'deg';

            case 'rotatez':  // in degrees
                throw "TODO: Sorry, math people. I really need help here! Please implement this case for me. This will help you: http://9elements.com/html5demos/matrix3d/";

            case 'translatex': // in pixels
                return matrix.m41 + 'px';

            case 'translatey': // in pixels
                return matrix.m42 + 'px';

            case 'translatez': // in pixels
                return matrix.m43 + 'px';

            case 'scale': // no units
                if (matrix.m11 === matrix.m22 && matrix.m22 === matrix.m33) {
                    return matrix.m11;
                } else {
                    throw "I'm not so smart to calculate scale from this matrix";
                }

           // todo: anything else? skew ????

            default:
                throw "This function accepts 3d-parameter name (case-insensitive string) as the second argument. Currently supported: 'rotate[xyz]', 'translate[xyz]', 'scale'. This parameter is unsupported: " + parameterName;
        }
    };