c#绘制多个图像到picturebox中，不需要平铺

我试图使用点绘制多个(20个小图像或更多)到单个图片框中，但是当我这样做时，它会复制图片框的每一行上的顶行。我已经到处搜索，并尝试了很多次，以得到这个正确的，但我不能弄清楚，谁可以帮助指出我在正确的方向?

我想完成的是:

1. image1 image2 image3 image4 image1
2. image2 image4 image1 image3 image3
3. image4 image7 image2 image1 image6
4. image3 image7 image3 image7 image6

但是我得到的是:

1. image1 image2 image3 image4 image1
2. image1 image2 image3 image4 image1
3. image1 image2 image3 image4 image1
4. image1 image2 image3 image4 image1

(当然没有数字)这里是我使用的代码

private void Form_Load(object sender, EventArgs e)
{
    Image[] Files = new Image[7]; 
    Bitmap a = new Bitmap(@"C:'icons'icon1.png");
    Files[0] = new Bitmap(a, 80, 80);
    image1 = Files[0];
    Bitmap b = new Bitmap(@"C:'icons'icon2.png");
    Files[1] = new Bitmap(b, 80, 80);
    image2 = Files[1];
    Bitmap c = new Bitmap(@"C:'icons'icon3.png");
    Files[2] = new Bitmap(c, 80, 80);
    image3 = Files[2];
    Bitmap d = new Bitmap(@"C:'icons'icon4.png");
    Files[3] = new Bitmap(d, 80, 80);
    image4 = Files[3];
    Bitmap h = new Bitmap(@"C:'icons'icon5.png");
    Files[4] = new Bitmap(h, 80, 80);
    image5 = Files[4];
    Bitmap f = new Bitmap(@"C:'icons'icon6.png");
    Files[5] = new Bitmap(f, 80, 80);
    image6 = Files[5];
    Bitmap g = new Bitmap(@"C:'icons'icon7.png");
    Files[6] = new Bitmap(g, 80, 80);
    image7 = Files[6];
    pictureBox1.BackgroundImage = CombineBitmap(Files);
}
public static System.Drawing.Bitmap CombineBitmap(Image[] files)
    {
        List<System.Drawing.Bitmap> images = new List<System.Drawing.Bitmap>();
        System.Drawing.Bitmap finalImage = null;
        try
        {
            int width = 0;
            int height = 0;
            foreach (Image image in files)
            {
                System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(image);
                width += bitmap.Width;
                height = bitmap.Height > height ? bitmap.Height : height;
                images.Add(bitmap);
            }
            finalImage = new System.Drawing.Bitmap(width, height);
            using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(finalImage))
            {
                g.Clear(System.Drawing.Color.Gray); // Change this to whatever you want the background color to be, you may set this to Color.Transparent as well
                int offset = 15;
                Point p1 = new Point(0, 0);
                Point p2 = new Point(80, 0);
                Point p3 = new Point(160, 0);
                Point p4 = new Point(240, 0);
                Point p5 = new Point(320, 0);
                Point p6 = new Point(0, 80);
                Point p7 = new Point(80, 80);
                Point p8 = new Point(160, 80);
                Point p9 = new Point(240, 80);
                Point p10 = new Point(320, 80);
                Point p11 = new Point(0, 160);
                Point p12 = new Point(80, 160);
                Point p13 = new Point(160, 160);
                Point p14 = new Point(240, 160);
                Point p15 = new Point(320, 160);
                Point p16 = new Point(0, 240);
                Point p17 = new Point(80, 240);
                Point p18 = new Point(160, 240);
                Point p19 = new Point(240, 240);
                Point p20 = new Point(320, 240);

                g.DrawImage(image1, p1);
                g.DrawImage(image2, p2);
                g.DrawImage(image3, p3);
                g.DrawImage(image4, p4);
                g.DrawImage(image1, p5);

                g.DrawImage(image2, p6);
                g.DrawImage(image4, p7);
                g.DrawImage(image1, p8);
                g.DrawImage(image3, p9);
                g.DrawImage(image3, p10);
                g.DrawImage(image4, p11);
                g.DrawImage(image7, p12);
                g.DrawImage(image2, p13);
                g.DrawImage(image1, p14);
                g.DrawImage(image6, p15);
                g.DrawImage(image3, p16);
                g.DrawImage(image7, p17);
                g.DrawImage(image3, p18);
                g.DrawImage(image7, p19);
                g.DrawImage(image6, p20);
               }
            return finalImage;
        }
        catch (Exception ex)
        {
            if (finalImage != null)
                finalImage.Dispose();
            throw ex;
        }
        finally
        {
            foreach (System.Drawing.Bitmap image in images)
            {
                image.Dispose();
            }
        }
    }

finalImage = new System.Drawing.Bitmap(400, 320);