4. 膨脹處理程式

顏色不能直接 ==，要 ToArgb()

namespace Q4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            openFileDialog1.ShowDialog();
            pictureBox1.Image = Bitmap.FromFile(openFileDialog1.FileName);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            var bm = (Bitmap)pictureBox1.Image;
            Bitmap nbm = (Bitmap)bm.Clone();
            for (int x = 0; x < bm.Width; x++)
                for (int y = 0; y < bm.Height; y++)
                {
                    processPixel(bm, nbm, x, y);
                }
            pictureBox1.Image = nbm;
        }

        void processPixel(Bitmap bm, Bitmap nbm, int x, int y)
        {
            var c = bm.GetPixel(x, y);
            if (c.ToArgb() == Color.White.ToArgb()) return;
            setPixel(nbm, c, x + 1, y);
            setPixel(nbm, c, x, y + 1);
            setPixel(nbm, c, x, y - 1);
            setPixel(nbm, c, x - 1, y);
            setPixel(nbm, c, x + 1, y + 1);
            setPixel(nbm, c, x - 1, y - 1);
            setPixel(nbm, c, x + 1, y - 1);
            setPixel(nbm, c, x - 1, y + 1);
        }

        void setPixel(Bitmap bm, Color source, int x, int y)
        {
            if (x < 0 || x >= bm.Width) return;
            if (y < 0 || y >= bm.Height) return;
            var c = bm.GetPixel(x, y);
            if (c.ToArgb()!=Color.White.ToArgb()) return;
            bm.SetPixel(x, y, source);
        }
    }
}