C# 透明窗体桌面画图(矩形框选)

【实例截图】

【核心代码】

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

namespace mousdraw
{
    public partial class Form1 : Form
    {
        private bool startdraw = false;//是否开始画图
        private Graphics gs;//画版
        private Pen pen;//画笔
        private Point startpt;//画图起点
        public Rectangle taskBarRect;//任务栏位置
        public Form1()
        {
            InitializeComponent();
            WindowState = FormWindowState.Maximized;//本窗体最大化
            FormBorderStyle = FormBorderStyle.None;//无边框窗体
            
            TransparencyKey = BackColor;//背景透明(鼠标穿透)
            DoubleBuffered = true;//双缓存处理

            gs = CreateGraphics();//创建窗体画板
            pen = new Pen(Color.Black, 3f);//画笔

            //taskBarHandle为返回的任务栏的句柄  
            //Shell_TrayWnd为任务栏的类名  
            MouseHookProcedure = new HookProc(MouseHookProc); //声明钩子 
            int taskBarHandle = FindWindow("Shell_TrayWnd", null);
            GetWindowRect(taskBarHandle, ref taskBarRect);
            newTaskBarRect = new Rectangle(taskBarRect.X, taskBarRect.Y, taskBarRect.Width - taskBarRect.X, taskBarRect.Height - taskBarRect.Y);
            StartHook();
        }


        private int hMouseHook = 0;
        private MouseEventArgs mea;//鼠标事件参数
        //全局钩子常量  
        private const int WH_MOUSE_LL = 14;

        //声明消息的常量,鼠标按下和释放  
        private const int WM_LEFT_RBUTTONDOWN = 0x201;//鼠标左键按下事件监听值
        private const int WM_LEFT_RBUTTONUP = 0x202;//鼠标左键弹起事件监听值
        private const int WM_RIGHT_RBUTTONDOWN = 0x204;//鼠标右键按下事件监听值
        private const int WM_RIGHT_RBUTTONUP = 0x205;//鼠标右键按下事件监听值
        private const int WM_MOVE = 0x200;//鼠标移动事件监听值

        //保存任务栏的矩形区域  

        public Rectangle newTaskBarRect;

        //定义委托  
        public delegate int HookProc(int nCode, int wParam, IntPtr lParam);
        private HookProc MouseHookProcedure;

        //寻找符合条件的窗口  
        [DllImport("user32.dll", EntryPoint = "FindWindow")]
        public static extern int FindWindow(
            string lpClassName,
            string lpWindowName
        );

        //获取窗口的矩形区域  
        [DllImport("user32.dll", EntryPoint = "GetWindowRect")]
        public static extern int GetWindowRect(
            int hwnd,
            ref Rectangle lpRect
        );

        //安装钩子  
        [DllImport("user32.dll")]
        public static extern int SetWindowsHookEx(
            int idHook,
            HookProc lpfn,
            IntPtr hInstance,
            int threadId
        );

        //卸载钩子  
        [DllImport("user32.dll", EntryPoint = "UnhookWindowsHookEx")]
        public static extern bool UnhookWindowsHookEx(
            int hHook
        );

        //调用下一个钩子  
        [DllImport("user32.dll")]
        public static extern int CallNextHookEx(
            int idHook,
            int nCode,
            int wParam,
            IntPtr lParam
        );

        //获取当前线程的标识符  
        [DllImport("kernel32.dll")]
        public static extern int GetCurrentThreadId();

        //获取一个应用程序或动态链接库的模块句柄  
        [DllImport("kernel32.dll")]
        public static extern IntPtr GetModuleHandle(string name);

        //鼠标结构，保存了鼠标的信息  
        [StructLayout(LayoutKind.Sequential)]
        public struct MOUSEHOOKSTRUCT
        {
            public Point pt;
            public int hwnd;
            public int wHitTestCode;
            public int dwExtraInfo;
        }

        /// <summary>  
        /// 安装钩子  
        /// </summary>  
        private void StartHook()
        {
            if (hMouseHook == 0)
            {
                hMouseHook = SetWindowsHookEx(WH_MOUSE_LL, MouseHookProcedure, GetModuleHandle(Process.GetCurrentProcess().MainModule.ModuleName), 0);
                if (hMouseHook == 0)
                {//如果设置钩子失败.   
                    this.StopHook();
                    MessageBox.Show("Set windows hook failed!");
                }
            }
        }

        /// <summary>  
        /// 卸载钩子  
        /// </summary>  
        private void StopHook()
        {
            bool stop = true;

            if (hMouseHook != 0)
            {
                stop = UnhookWindowsHookEx(hMouseHook);
                hMouseHook = 0;

                if (!stop)
                {//卸载钩子失败  
                    MessageBox.Show("Unhook failed!");
                }
            }
        }

        private int MouseHookProc(int nCode, int wParam, IntPtr lParam)
        {
            if (nCode >= 0)
            {
                //把参数lParam在内存中指向的数据转换为MOUSEHOOKSTRUCT结构  
                MOUSEHOOKSTRUCT mouse = (MOUSEHOOKSTRUCT)Marshal.PtrToStructure(lParam, typeof(MOUSEHOOKSTRUCT));//鼠标  
                mea = new MouseEventArgs(MouseButtons.Left, 1, mouse.pt.X, mouse.pt.Y, 0);
                //这句为了看鼠标的位置  
                this.Text = "MousePosition:"   mouse.pt.ToString();
                mousdraw_MouseMove(mea);


                if (wParam == WM_LEFT_RBUTTONDOWN || wParam == WM_LEFT_RBUTTONUP || wParam == WM_RIGHT_RBUTTONDOWN || wParam == WM_RIGHT_RBUTTONUP)
                { //鼠标按下或者释放时候截获  

                    if (newTaskBarRect.Contains(mouse.pt))
                    { //当鼠标在任务栏的范围内  
                        //如果返回1，则结束消息，这个消息到此为止，不再传递。  
                        //如果返回0或调用CallNextHookEx函数则消息出了这个钩子继续往下传递，也就是传给消息真正的接受者  
                        return 0;
                    }
                    else if (wParam == WM_LEFT_RBUTTONDOWN)
                    {
                        return mousdraw_MouseDown(mea);
                    }
                    else if (wParam == WM_LEFT_RBUTTONUP)
                    {
                        return mousdraw_MouseUp(mea);
                    }
                    else
                    {
                        return 1;
                    }
                }
            }
            return CallNextHookEx(hMouseHook, nCode, wParam, lParam);
        }

        private int mousdraw_MouseDown(MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                startdraw = true;//开始画图
                startpt = e.Location;
            }
            return 1;
        }

        private int mousdraw_MouseMove(MouseEventArgs e)
        {
            if (startdraw)
            {
                gs.DrawLine(pen, startpt, e.Location);
                startpt = e.Location;
            }
            return 0;
        }

        private int mousdraw_MouseUp(MouseEventArgs e)
        {
            startdraw = false;//结束画图
            return 1;
        }

    }
}