示例：绘制2.5D地图网格辅助线

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

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

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            DrawMapGrid(e.Graphics, 8, 6, 64, 32);
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //当窗口尺寸改变时重绘所有窗口
            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.ResizeRedraw, true);
        }

        private void DrawMapGrid(Graphics g, Rectangle mapRect, int gridWidth, int gridHeight)
        {
            int rowCount = mapRect.Height / gridHeight;
            int colCount = mapRect.Width / gridWidth;
            DrawMapGrid(g, rowCount, colCount, gridWidth, gridHeight);
        }

        private void DrawMapGrid(Graphics g, int rowCount, int colCount, int gridWidth, int gridHeight)
        {
            Pen pen = new Pen(Brushes.Black);
            Point p1;
            Point p2;

            List<Point> vertexs = CalMapVertexs(g, rowCount, colCount, gridWidth, gridHeight);
            int maxVertIndex = vertexs.Count - 1;

            //绘制斜线
            for (int i = 0; i < colCount + rowCount; i++)
            {
                p1 = vertexs[i];
                p2 = vertexs[maxVertIndex - i];
                g.DrawLine(pen, p1, p2);
            }

            //绘制反斜线
            int index1 = colCount - 1;
            int index2 = colCount;
            for (int i = 0; i < colCount + rowCount; i++)
            {
                int startIndex = index1 - i;
                if (startIndex < 0)
                    startIndex += vertexs.Count;
                p1 = vertexs[startIndex];
                p2 = vertexs[index2 + i];
                g.DrawLine(pen, p1, p2);
            }
        }

        private List<Point> CalMapVertexs(Graphics g, int rowCount, int colCount, int gridWidth, int gridHeight)
        {
            Pen pen = new Pen(Brushes.Black);

            Point p = new Point(gridWidth / 2, 0);
            List<Point> vertexs = new List<Point>();

            //计算上边顶点坐标
            for (int i = 0; i < colCount; i++)
            {
                g.DrawEllipse(pen, p.X, p.Y, 5, 5);
                vertexs.Add(new Point(p.X, p.Y));
                p.X += gridWidth;
            }

            //计算右侧顶点坐标
            p.X -= gridWidth / 2;
            p.Y = gridHeight / 2;
            for (int i = 0; i < rowCount; i++)
            {
                g.DrawEllipse(pen, p.X, p.Y, 5, 5);
                vertexs.Add(new Point(p.X, p.Y));
                p.Y += gridHeight;
            }

            //计算下边顶点坐标
            p.X -= gridWidth / 2;
            p.Y -= gridHeight / 2;
            for (int i = 0; i < colCount; i++)
            {
                g.DrawEllipse(pen, p.X, p.Y, 5, 5);
                vertexs.Add(new Point(p.X, p.Y));
                p.X -= gridWidth;
            }

            //计算左侧坐标
            p.X = 0;
            p.Y -= gridHeight / 2;
            for (int i = 0; i < rowCount; i++)
            {
                g.DrawEllipse(pen, p.X, p.Y, 5, 5);
                vertexs.Add(new Point(p.X, p.Y));
                p.Y -= gridHeight;
            }

            return vertexs;
        }
    }
}

运行效果