matrix preXXX and postXXX

matrix

matrix代表一个3*3矩阵，其内容如下
MSCALE_X  MSKEW_X   MTRANS_X

MSKEW_Y   MSKEW_Y   MTRANS_Y

MPERSP_0  MPERSP_1  MPERSP_2

    Matrix matrix=new Matrix();
		System.err.println(matrix.toShortString());
		matrix.postScale(2, 3);
		System.err.println(matrix.toShortString());
		matrix.postTranslate(10, 10);
		System.err.println(matrix.toShortString());
		
		计算过程如下
		2  0  0      1  0  0    2  0  0
		0  3  0   *  0  1  0  = 0  3  0
		0  0  1      0  0  1    0  0  1
		
		1  0  10     2  0  0    2  0  10
		0  1  10  *  0  3  0  = 0  3  10
		0  0  1      0  0  1    0  0  1
		
		matrix=new Matrix();
		System.err.println(matrix.toShortString());
		matrix.preScale(2, 3);
		System.err.println(matrix.toShortString());
		matrix.preTranslate(10, 10);
		System.err.println(matrix.toShortString());
		
		计算过程如下
		1  0  0      2  0  0    2  0  0
		0  1  0   *  0  3  0  = 0  3  0
		0  0  1      0  0  1    0  0  1
		
		2  0  0      1  0  10    2  0  20
		0  3  0  *   0  1  10  = 0  3  30
		0  0  1      0  0  1     0  0  1
		
		所以prexxx或者postxxx方法先在单位矩阵的基础上生成一个矩阵M'。方法中参数的值会被设置到对应的位置（见开头）。
		假定原始矩阵为M，则
		matrix.prexxx(a,b)=M*M'
		matrix.postxxx（a,b）= M'*M
		
		

http://my.oschina.net/u/559701/blog/74245
http://www.useragentman.com/blog/2011/01/07/css3-matrix-transform-for-the-mathematically-challenged/