using System;
using System.Drawing;
using System.Windows.Forms;

namespace GdiPlusDemo
{
    public partial class Form1 : Form
    {
        private int radius = 50;
        private Point center;

        public Form1()
        {
            InitializeComponent();
            center = new Point(ClientSize.Width / 2, ClientSize.Height / 2);
            DoubleBuffered = true;
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            Graphics graphics = e.Graphics;
            graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            graphics.Clear(Color.White);
            graphics.DrawEllipse(Pens.Red,
                center.X - radius, center.Y - radius, radius * 2, radius * 2);
        }

        protected override void OnResize(EventArgs e)
        {
            base.OnResize(e);
            center = new Point(ClientSize.Width / 2, ClientSize.Height / 2);
            Invalidate();
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            if (e.Button == MouseButtons.Left)
            {
                radius += 10;
                Invalidate();
            }
            else if (e.Button == MouseButtons.Right)
            {
                radius -= 10;
                Invalidate();
            }
        }
    }
}

public partial class lblFont : Form
{
    int index = 0;
    public lblFont()
    {
        InitializeComponent();
        SetStyle(ControlStyles.UserPaint, true);
        SetStyle(ControlStyles.AllPaintingInWmPaint, true); // 禁止擦除背景.
        SetStyle(ControlStyles.DoubleBuffer, true); // 双缓冲
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        Graphics graphics = e.Graphics;
        switch (index)
        {
            case 0:
                Rectangle rectangle = new Rectangle(0, 0, 400, 400);
                graphics.FillRectangle(Brushes.Black, rectangle);
                break;
            case 1:
                rectangle = new Rectangle(0, 0, 200, 200);
                graphics.FillRectangle(Brushes.Black, rectangle);
                break;
            case 2:
                rectangle = new Rectangle(0, 0, 100, 100);
                graphics.FillRectangle(Brushes.Black, rectangle);
                break;
        }

    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        index = comboBox1.SelectedIndex;
        this.Invalidate();
        this.Update();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        comboBox1.SelectedIndex = 0;
    }
}