详解C#如何实现屏幕放大和取色功能

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

    #region 定义快捷键
    //如果函数执行成功，返回值不为0。       
    //如果函数执行失败，返回值为0。要得到扩展错误信息，调用GetLastError。        
    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool RegisterHotKey(
    IntPtr hWnd,                //要定义热键的窗口的句柄            
    int id,                     //定义热键ID（不能与其它ID重复）                       
    KeyModifiers fsModifiers,   //标识热键是否在按Alt、Ctrl、Shift、Windows等键时才会生效         
    Keys vk                     //定义热键的内容            
);
    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool UnregisterHotKey(
        IntPtr hWnd,                //要取消热键的窗口的句柄            
        int id                      //要取消热键的ID            
    );
    //定义了辅助键的名称（将数字转变为字符以便于记忆，也可去除此枚举而直接使用数值）        
    [Flags()]
    public enum KeyModifiers
    {
        None = 0,
        Alt = 1,
        Ctrl = 2,
        Shift = 4,
        WindowsKey = 8
    }
    #endregion

    #region 获取鼠标像素的RGB
    [DllImport("gdi32.dll")]
    static public extern uint GetPixel(IntPtr hDC, int XPos, int YPos);
    [DllImport("gdi32.dll")]
    static public extern IntPtr CreateDC(string driverName, string deviceName, string output, IntPtr lpinitData);
    [DllImport("gdi32.dll")]
    static public extern bool DeleteDC(IntPtr DC);
    static public byte GetRValue(uint color)
    {
        return (byte)color;
    }
    static public byte GetGValue(uint color)
    {
        return ((byte)(((short)(color)) >> 8));
    }
    static public byte GetBValue(uint color)
    {
        return ((byte)((color) >> 16));
    }
    static public byte GetAValue(uint color)
    {
        return ((byte)((color) >> 24));
    }
    public Color GetColor(Point screenPoint)
    {
        IntPtr displayDC = CreateDC("DISPLAY", null, null, IntPtr.Zero);
        uint colorref = GetPixel(displayDC, screenPoint.X, screenPoint.Y);
        DeleteDC(displayDC);
        byte Red = GetRValue(colorref);
        byte Green = GetGValue(colorref);
        byte Blue = GetBValue(colorref);
        return Color.FromArgb(Red, Green, Blue);
    }
    #endregion

    
    int screenWidth;        //屏幕宽度
    int screenHeight;       //屏幕高度
    int mx;                 //鼠标x坐标
    int my;                 //鼠标y坐标
    const int imgWidth = 234;//放大后图片的宽度
    const int imgHeight = 134;//放大后图片的高度

    private void Form1_Load(object sender, EventArgs e)
    {
        this.Location = new Point(0,0);
        screenWidth = Screen.PrimaryScreen.WorkingArea.Width;
        screenHeight = Screen.PrimaryScreen.WorkingArea.Height;
        this.TopMost = true;
    }

    private void timer1_Tick(object sender, EventArgs e)
    {
        RegisterHotKey(Handle, 81, KeyModifiers.None, Keys.Escape);
        mx = Control.MousePosition.X;
        my = Control.MousePosition.Y;
        lblmPos.Text="("+mx.ToString()+","+my.ToString()+")";
        Point pt = new Point(mx,my);
        Color cl = GetColor(pt);
        lblRGB.Text = "(" + cl.R.ToString() + "," + cl.G.ToString() + "," + cl.B + ")";
        if (mx <= this.Width&&my<=this.Height)
        {
            this.Location = new Point(screenWidth-this.Width,0);
        }
        if (mx >= screenWidth - this.Width&&my<=this.Height)
        {
            this.Location = new Point(0,0);
        }
        Bitmap bt = new Bitmap(imgWidth/2,imgHeight/2);
        Graphics g = Graphics.FromImage(bt);
        g.CopyFromScreen(new Point(Cursor.Position.X-imgWidth/4,Cursor.Position.Y-imgHeight/4),new Point(0,0),new Size(imgWidth/2,imgHeight/2));
        IntPtr dc1 = g.GetHdc();
        g.ReleaseHdc(dc1);
        pictureBox1.Image = (Image)bt;
       
    }

    protected override void WndProc(ref Message m)
    {
        const int WM_HOTKEY = 0x0312;
        //按快捷键     
        switch (m.Msg)
        {
            case WM_HOTKEY:
                switch (m.WParam.ToInt32())
                {
                    case 81:    //按下的是ESC     
                        Application.Exit();
                        break;
                }
                break;
        }
        base.WndProc(ref m);
    }

    private void Form1_FormClosed(object sender, FormClosedEventArgs e)
    {
        //注销Id号为81的热键设定    
        UnregisterHotKey(Handle, 81);
    }

    private void pictureBox1_Paint(object sender, PaintEventArgs e)
    {
        Graphics g = e.Graphics;
        g.DrawLine(new Pen(Color.Red), new PointF(pictureBox1.Width / 2, 0), new PointF(pictureBox1.Width / 2,pictureBox1.Height));
        g.DrawLine(new Pen(Color.Red,2), new PointF(0, pictureBox1.Height / 2), new PointF(pictureBox1.Width, pictureBox1.Height/2));
    }
}

partial class Form1
    {
        /// <summary>
        /// 必需的设计器变量。
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// 清理所有正在使用的资源。
        /// </summary>
        /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗体设计器生成的代码

        /// <summary>
        /// 设计器支持所需的方法 - 不要
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.timer1 = new System.Windows.Forms.Timer(this.components);
            this.label2 = new System.Windows.Forms.Label();
            this.lblmPos = new System.Windows.Forms.Label();
            this.label3 = new System.Windows.Forms.Label();
            this.label4 = new System.Windows.Forms.Label();
            this.lblRGB = new System.Windows.Forms.Label();
            this.pictureBox1 = new System.Windows.Forms.PictureBox();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
            this.SuspendLayout();
            // 
            // timer1
            // 
            this.timer1.Enabled = true;
            this.timer1.Tick += new System.EventHandler(this.timer1_Tick);
            // 
            // label2
            // 
            this.label2.AutoSize = true;
            this.label2.BackColor = System.Drawing.Color.Transparent;
            this.label2.ForeColor = System.Drawing.Color.Black;
            this.label2.Location = new System.Drawing.Point(12, 122);
            this.label2.Name = "label2";
            this.label2.Size = new System.Drawing.Size(65, 12);
            this.label2.TabIndex = 2;
            this.label2.Text = "鼠标位置：";
            // 
            // lblmPos
            // 
            this.lblmPos.AutoSize = true;
            this.lblmPos.BackColor = System.Drawing.Color.Transparent;
            this.lblmPos.ForeColor = System.Drawing.Color.Black;
            this.lblmPos.Location = new System.Drawing.Point(83, 122);
            this.lblmPos.Name = "lblmPos";
            this.lblmPos.Size = new System.Drawing.Size(41, 12);
            this.lblmPos.TabIndex = 3;
            this.lblmPos.Text = "label3";
            // 
            // label3
            // 
            this.label3.AutoSize = true;
            this.label3.BackColor = System.Drawing.Color.Transparent;
            this.label3.ForeColor = System.Drawing.Color.Black;
            this.label3.Location = new System.Drawing.Point(10, 47);
            this.label3.Name = "label3";
            this.label3.Size = new System.Drawing.Size(125, 12);
            this.label3.TabIndex = 5;
            this.label3.Text = "⊙ 当前像素的RGB值：";
            // 
            // label4
            // 
            this.label4.AutoSize = true;
            this.label4.BackColor = System.Drawing.Color.Transparent;
            this.label4.ForeColor = System.Drawing.Color.Black;
            this.label4.Location = new System.Drawing.Point(10, 73);
            this.label4.Name = "label4";
            this.label4.Size = new System.Drawing.Size(125, 12);
            this.label4.TabIndex = 6;
            this.label4.Text = "⊙ 按ESC键关闭放大镜";
            // 
            // lblRGB
            // 
            this.lblRGB.AutoSize = true;
            this.lblRGB.BackColor = System.Drawing.Color.Transparent;
            this.lblRGB.ForeColor = System.Drawing.Color.Black;
            this.lblRGB.Location = new System.Drawing.Point(129, 47);
            this.lblRGB.Name = "lblRGB";
            this.lblRGB.Size = new System.Drawing.Size(41, 12);
            this.lblRGB.TabIndex = 7;
            this.lblRGB.Text = "label5";
            // 
            // pictureBox1
            // 
            this.pictureBox1.BackColor = System.Drawing.Color.White;
            this.pictureBox1.Location = new System.Drawing.Point(3, 146);
            this.pictureBox1.Name = "pictureBox1";
            this.pictureBox1.Size = new System.Drawing.Size(234, 134);
            this.pictureBox1.SizeMode = System.Windows.Forms.PictureBoxSizeMode.Zoom;
            this.pictureBox1.TabIndex = 8;
            this.pictureBox1.TabStop = false;
            this.pictureBox1.Paint += new System.Windows.Forms.PaintEventHandler(this.pictureBox1_Paint);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.BackgroundImage = global::ScreenBlowupGlass.Properties.Resources.bg;
            this.ClientSize = new System.Drawing.Size(241, 284);
            this.Controls.Add(this.pictureBox1);
            this.Controls.Add(this.lblRGB);
            this.Controls.Add(this.label4);
            this.Controls.Add(this.label3);
            this.Controls.Add(this.lblmPos);
            this.Controls.Add(this.label2);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            this.MaximizeBox = false;
            this.MinimizeBox = false;
            this.Name = "Form1";
            this.Text = "屏幕放大镜";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.FormClosed += new System.Windows.Forms.FormClosedEventHandler(this.Form1_FormClosed);
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Timer timer1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.Label lblmPos;
        private System.Windows.Forms.Label label3;
        private System.Windows.Forms.Label label4;
        private System.Windows.Forms.Label lblRGB;
        private System.Windows.Forms.PictureBox pictureBox1;
    }