怎么在Android利用Matrix对图片进行旋转

package com.oyp.loadingdisk;  import java.io.InputStream;  import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Matrix; import android.graphics.Paint; import android.graphics.PaintFlagsDrawFilter; import android.view.View;  public class LoadingDiscView extends View {   private RefreshHandle refreshHandle;   private Context context;      private Bitmap m_bmp_disc = null;   private Matrix m_matrix_disc = new Matrix();      private Bitmap m_bmp_light = null;   private Matrix m_matrix_light = new Matrix();      private PaintFlagsDrawFilter mSetfil = null;      private Paint mypaint = null;      private float m_scale =1.0f;      private float m_disc_rot_speed = 0;      private int m_state_play = 1;      private float m_disc_max = 20f;    public void setRefreshHandle(RefreshHandle refreshHandle) {    this.refreshHandle = refreshHandle;   }    public LoadingDiscView(Context context) {    super(context);    this.context = context;    mSetfil = new PaintFlagsDrawFilter(0, Paint.FILTER_BITMAP_FLAG);//设置画布绘图无锯齿    initBitmap();   }    public boolean initBitmap() {    mypaint = new Paint();    //给Paint加上抗锯齿标志    mypaint.setAntiAlias(true);//画笔的抗锯齿（用于线条等）     Resources res = context.getResources();    InputStream is = res.openRawResource(R.drawable.loading_disc);    m_bmp_disc = BitmapFactory.decodeStream(is);    matrixPostTranslate(m_matrix_disc,m_bmp_disc);     is = res.openRawResource(R.drawable.loading_light);    m_bmp_light = BitmapFactory.decodeStream(is);    matrixPostTranslate(m_matrix_light,m_bmp_light);    return true;   }      private void matrixPostTranslate(Matrix matrix,Bitmap bitmap) {    int tmp_width = bitmap.getWidth();    int tmp_height = bitmap.getHeight();    matrix.postTranslate(-tmp_width / 2, -tmp_height / 2); //设置平移位置    matrix.postScale(m_scale, m_scale); //设置缩放比例    matrix.postTranslate(123 * m_scale, 146 * m_scale);   }    protected void onDraw(Canvas canvas) {    super.onDraw(canvas);    //给Canvas加上抗锯齿标志    canvas.setDrawFilter(mSetfil);//图片线条（通用）的抗锯齿    canvas.drawBitmap(m_bmp_disc, m_matrix_disc, mypaint);    canvas.drawBitmap(m_bmp_light, m_matrix_light, mypaint);   }    public void update() {    if (m_disc_rot_speed > 0.01 || m_state_play == 1){     if (m_state_play == 1 && m_disc_rot_speed<m_disc_max){      m_disc_rot_speed += (m_disc_max+0.5f-m_disc_rot_speed)/30;     }     else if (m_disc_rot_speed>0.1){      m_disc_rot_speed -= (m_disc_rot_speed)/40;     }     m_matrix_disc .postRotate(m_disc_rot_speed, 123*m_scale, 146*m_scale);     invalidate();    }   }      public void onPause(){    refreshHandle.stop();   }   public void onResume(){    refreshHandle.run();   }     }