CSS transform polyfill (work in progress)

cssTransform.polyfill.js

;(function(window, document, Math, undefined) {
  var ORIGIN_PATTERN = /\s*(-?[0-9.]+)(%?)\s+(-?[0-9.]+)(%?)\s*/;
  var TRANSFORM_PATTERNS = [
    /(matrix)\(\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*\)/,
    /(translate)\(\s*(-?[0-9.]+)\s*,\s*(-?[0-9.]+)\s*\)/,
    /(rotate|skew[XY])\(\s*(-?[0-9.]+)(deg|g?rad|turn)\s*\)/,
    /(scale)\(\s*(-?[0-9.]+)(%?)\s*(?:,\s*(-?[0-9.]+)(%?)\s*)\)/
  ];
  var TRANSFORM_FUNCTIONS = {
    matrix: function (v0, v1, v2, v3, dx, dy) {
      return [ v0, v1, v2, v3, dx, dy ];
    },
    translate: function (dx, dy) {
      return [ 1, 0, 0, 1, dx, dy ];
    },
    rotate: function (value, unit) {
      var angle = parseAngle(value, unit);
      var cos = Math.cos(angle);
      var sin = Math.sin(angle);
      return [ cos, -sin, sin, cos, 0, 0 ];
    },
    skewX: function (value, unit) {
      return [ 1, 0, Math.tan(parseAngle(value, unit)), 1, 0, 0 ];
    },
    skewY: function (value, unit) {
      return [ 1, Math.tan(parseAngle(value, unit)), 0, 1, 0, 0 ];
    },
    scale: function (x, unitx, y, unity) {
      var fx = parseFactor(x, unitx);
      var fy = sy === undefined ? fx : parseFactor(y, unity);
      return [ fx, 0, 0, fy, 0, 0 ];
    }
  };

  /* simplified matrix multiplication
   * for 3x3 matrices of the form
   * / v0 v1 0 \
   * | v2 v3 0 |
   * \ dx dy 1 /
   * each matrix is supplied as a 6-vector
   * containing the values v0 to v3, dx and dy
   */
  function mmult(M1, M2) {
    return [ M1[0]*M2[0] + M1[1]*M2[2], M1[0]*M2[1] + M1[1]*M2[3],
             M1[2]*M2[0] + M1[3]*M2[2], M1[2]*M2[1] + M1[3]*M2[3],
             M1[4]*1     + M2[4]*1,     M1[5]*1     + M2[5]*1 ];
  }

  function mfilter(M) {
    return ( 'progid:DXImageTransform.Microsoft.Matrix('
           + 'M11=' + M[0] + ','
           + 'M12=' + M[2] + ','
           + 'M21=' + M[1] + ','
           + 'M22=' + M[3] + ',SizingMethod=\'auto expand\')' );
  }

  function parseAngle(value, unit) {
    return {
      'deg': Math.PI / 180,
      'grad': Math.PI / 200,
      'turn': Math.PI * 2,
      'rad': 1
    }[ unit ] * value;
  }

  function parseFactor(value, unit) {
    return (unit === '%') ? value / 100 : value * 1;
  }

  function adjustStylePx(element, property, delta) {
    element.style[property] = (delta|0 + parseInt(element.currentStyle[property], 10)|0) + 'px';
  }

  function adjustElementPosition(element, matrix, origin) {
    var x = element.clientWidth * origin.x;
    var y = element.clientHeight * origin.y;
    var left = -x;
    var right = element.clientWidth - x;
    var top = -y;
    var bottom = element.clientHeight - y;

    var f = [
      matrix[0] * left,
      matrix[0] * right,
      matrix[2] * top,
      matrix[2] * bottom,
      matrix[1] * left,
      matrix[1] * right,
      matrix[3] * top,
      matrix[3] * bottom
    ];

    var minx = Math.min(f[0], f[1]) + Math.min(f[2], f[3]);
    var miny = Math.min(f[4], f[5]) + Math.min(f[6], f[7]);
    var maxx = Math.max(f[0], f[1]) + Math.max(f[2], f[3]);
    var maxy = Math.max(f[4], f[5]) + Math.max(f[6], f[7]);

    if (element.currentStyle.position !== 'absolute') {
      element.style.position = 'relative';
    }

    /* divide by two because IEs transform origin is always .5 .5 */
    adjustStylePx(element, 'marginLeft', (minx - left)/2);
    adjustStylePx(element, 'marginTop', (miny - top)/2);
    adjustStylePx(element, 'marginRight', (right - maxx)/2);
    adjustStylePx(element, 'marginBottom', (bottom - maxy)/2);

    adjustStylePx(element, 'left', matrix[4]);
    adjustStylePx(element, 'top', matrix[5]);
  }

  function applyTransform(rule, transform, transformOrigin) {
    var i, match, offset, elements;
    var matrix = [ 1, 0, 0, 1, 0, 0 ];
    var origin = { x: 0.5, y: 0.5 };

    for (i=0; i<TRANSFORM_PATTERNS.length; i++) {
      offset = 0;
      while ((match = TRANSFORM_PATTERNS[ i ].exec(transform.substr(offset)))) {
        offset += match.shift().length;
        matrix = mmult( matrix, TRANSFORM_FUNCTIONS[ match.shift() ].apply(null, match) );
      }
    }
    if ((match = ORIGIN_PATTERN.exec(transformOrigin))) {
      origin.x = parseFactor(match[1], match[2]);
      origin.y = parseFactor(match[3], match[4]);
    }

    elements = document.querySelectorAll(rule.selectorText);
    for (i=0; i < elements.length; i++) {
      adjustElementPosition(elements[i], matrix, origin);
    }
    rule.style.filter = (rule.style.filter ? rule.style.filter + ', ' : '') + mfilter(matrix);
  }

  var styleSheets = document.styleSheets;
  for (var i = 0; i < styleSheets.length; i++) {
    var styleSheet = styleSheets[i];
    var rules = styleSheet.rules;

    for (var j = 0; j < rules.length; j++) {
      var rule = rules[j];
      var style = rule.style;
      if (style.transform) {
        applyTransform(rule, style['transform'], style['transform-origin']);
      }
    }
  }
})(window, document, Math);

demo.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title></title>
  <style>

    .trapeze-container {
      position: relative;
    }

    .trapeze-container > .layer {
      position: absolute;
      left: 0;
      right: 0;
    }

    .trapeze {
      width: 100px;
      height: 150px;
      border: solid 1px #22d;
      background: #ddf;
      padding: 0;
      margin: 0;
      display: inline-block;

      /* IE: simulate inline-block */
      zoom: 1;
      *display: inline;
    }

    .trapeze.left {
      border-right: 0;
      margin-right: -2px;
      transform-origin: 0 0;
      transform: matrix( 1, 0, .3, 1, 0, 0 );
    }

    .trapeze.right {
      border-left: 0;
      margin-left: -2px;
      transform-origin: 0 0;
      transform: matrix( 1, 0, -.3, 1, 0, 0 );
    }

    .trapeze.half {
      background: #eef;
      height: 75px;
    }

  </style>
</head>
<body>
  <div class="trapeze-container">
    <div class="layer">
      <div class="trapeze left"></div>
      <div class="trapeze right"></div>
    </div>
    <div class="layer">
      <div class="trapeze left half"></div>
      <div class="trapeze right half"></div>
    </div>
  </div>

  <!--[if IE]>
  <script src="cssTransform.polyfill.js"></script>
  <![endif]-->
</body>
</html>

I've only implemented matrix(), scale(), rotate(), skewX(), skewY() and translate() tranforms so far, but the other ones should be easy to add.

Tested in IE8. Results might differ from modern rendering engines by a few pixels due to rounding and general IE suckage.

Also, if you want to have a 100%-solution for other old browsers, have a look at cssSandpaper

Removed inline-block polyfill, fixed rounding errors.

$ uglifyjs -m -c -- cssTransform.polyfill.js | tee cssTransform.polyfill.min.js | wc -c
2241