Matrix类在图形变换时很有用，《Pro Android Media》书的第55页有这样一段话：
The Matrix class represents transformations with an array of nine numbers. In many cases, these can be generated by a formula that mathematically represents the transformation that should occur. For instance, the formula for rotation involves using sine and cosine to generate the number in the matrix.
Each number in the Matrix applies to one of the three (x, y, or z) coordinates for each point in the image.
For instance, here is a Matrix of nine floats:
1 0 0
<br />0 1 0
<br />0 0 1
有点不太明白，为什么会有z轴？难道它还可以处理立体的图像吗？
书中第58页提到了一个wiki网页，讲了这种“矩阵变形”的原理：http://en.wikipedia.org/wiki/Transformation_matrix
晚点需要了解一下。