Function unmatrix

jquery.transform2d.js:370–418

(matrix)

// turns a matrix into its rotate, scale and skew components
// algorithm from http://hg.mozilla.org/mozilla-central/file/7cb3e9795d04/layout/style/nsStyleAnimation.cpp
function unmatrix(matrix) {
	var
			scaleX
		, scaleY
		, skew
		, A = matrix[0]
		, B = matrix[1]
		, C = matrix[2]
		, D = matrix[3]
		;

	// Make sure matrix is not singular
	if ( A * D - B * C ) {
		// step (3)
		scaleX = Math.sqrt( A * A + B * B );
		A /= scaleX;
		B /= scaleX;
		// step (4)
		skew = A * C + B * D;
		C -= A * skew;
		D -= B * skew;
		// step (5)
		scaleY = Math.sqrt( C * C + D * D );
		C /= scaleY;
		D /= scaleY;
		skew /= scaleY;
		// step (6)
		if ( A * D < B * C ) {
			A = -A;
			B = -B;
			skew = -skew;
			scaleX = -scaleX;
		}

	// matrix is singular and cannot be interpolated
	} else {
		// In this case the elem shouldn't be rendered, hence scale == 0
		scaleX = scaleY = skew = 0;
	}

	// The recomposition order is very important
	// see http://hg.mozilla.org/mozilla-central/file/7cb3e9795d04/layout/style/nsStyleAnimation.cpp#l971
	return [
		[_translate, [+matrix[4], +matrix[5]]],
		[_rotate, Math.atan2(B, A)],
		[_skew + "X", Math.atan(skew)],
		[_scale, [scaleX, scaleY]]
	];
}

// build the list of transform functions to interpolate
// use the algorithm described at http://dev.w3.org/csswg/css3-2d-transforms/#animation