绘制以某点为基准缩放

//缩放比例
float scale = 3f;
//缩放基于的点
int scalePointx = 30;
int scalePointy = 30;
Matrix matrix = new Matrix();
matrix.postTranslate(scalePointx,scalePointy);
matrix.postScale(scale,scale);
matrix.postTranslate(scalePointx*(1-scale),scalePointy*(1-scale));
canvas.setMatrix(matrix);