AndroidのMatrixクラスから、平行移動、拡縮、回転それぞれの成分を取り出す処理。射影変換の行列はサポート対象外です。

gistfile1.java

import android.graphics.Matrix;

public class MatrixUtils {

  public static Info decomposition(Matrix matrix, boolean reverseOrder) {

    double dx, dy, sx, sy, theta;

    float[] values = new float[9];
    matrix.getValues(values);

    if (values[Matrix.MPERSP_0] != 0 && values[Matrix.MPERSP_1] != 0 && values[Matrix.MPERSP_2] != 1) {
      throw new IllegalArgumentException("this matrix is not supported");
    }

    if (reverseOrder) {
      theta = Math.atan(values[3] / values[0]);
      double cos = Math.cos(theta);
      double sin = Math.sin(theta);

      dx = values[2] * cos + values[5] * sin;

      if (cos != 0.0) {
        sx = values[0] / cos;
        sy = values[4] / cos;
        dy = (values[5] - dx * sin) / cos;
      } else {
        sx = values[3] / sin;
        sy = -values[1] / sin;
        dy = (values[2] - dx * cos) / -sin;
      }
    } else {
      dx = values[2];
      dy = values[5];
      theta = Math.atan(-values[1] / values[0]);
      double cos = Math.cos(theta);
      double sin = Math.sin(theta);

      if (cos != 0.0) {
        sx = values[0] / cos;
        sy = values[4] / cos;
      } else {
        sx = -values[1] / sin;
        sy = values[3] / sin;
      }
    }

    return new Info(dx, dy, sx, sy, theta);
  }

  public static class Info {
    public final double dx;
    public final double dy;
    public final double sx;
    public final double sy;
    public final double theta;

    public Info(double dx, double dy, double sx, double sy, double theta) {
      this.dx = dx;
      this.dy = dy;
      this.sx = sx;
      this.sy = sy;
      this.theta = theta;
    }
  }
}