How to move a bitmap (like long green grass moving by the wind) fixing its pivot at the bottom center point of the bitmap in android? -

in application,i have long green grass bitmap.i have fix bitmap not move bottom part , should placed @ left bottom corner of screen.so have fix pivot @ bottom center of bitmap.after should move bitmap (like grass moving wind) left,some pixels , right,some pixels distance.but bitmap should not move pivot position.i unable fix pivot position , achieve grass moving.i posting code have done.please me solve this.

        private float direction = 1;           private float mangle = 0;   bitmap green_1 = bitmapfactory.decoderesource(getresources(),                 r.drawable.green_1);        private void drawpaper(canvas canvas){           paint paint=new paint();         paint.setantialias(true);         paint.setfilterbitmap(true);          if (mangle >= 3) {             direction=-0.2f;         } else if (mangle<=-3) {             direction=0.2f;         }         mangle = mangle + direction;          matrix matrix = new matrix();         matrix.posttranslate(0,heightofcanvas-green_1.getheight());         matrix.posttranslate(0, mangle);           canvas.drawbitmap(green_1, matrix, paint);        }         

thanks in advance.

just rotate canvas using :

canvas.rotate(deg, xpivot, ypivot) 

see : canvas#rotate(float, float, float)