实现推拉效果显示图片

        private void button1_Click(object sender,EventArgs e)
        {
            Bitmap myBitmap =(Bitmap)this.BackgroundImage.Clone();
            Graphics myGraphics = this.CreateGraphics();
            myGraphics.Clear(Color.Black);                                           //以指定颜色清除
            for (int i = 0; i < this.Height;i++ )                                    //从上到下遍历图片
            {
                Rectangle rectangle1 = new Rectangle(0,this.Width,i);           //获取图片指定行的像素
                Rectangle rectangle2 = new Rectangle(0,this.Height-i,i+1);//获取图片当前行的一下区域
                Bitmap bitmap = myBitmap.Clone(rectangle2,PixelFormat.DontCare);
                myGraphics.DrawImage(bitmap,rectangle1);                             //绘制指定大小的图片
                this.Show();
            }
        }