C# 如何纠正桌面上绘制矩形的错误

我想捕捉一个桌面区域，在桌面上画一个矩形

为了实现这一点，我开发了一个名为MouseHooker的类，它安装了一个全局鼠标钩子，处理鼠标消息，并通过一个委托回调将其公开

钩子代码还可以，我想外部的“回调”也可以，但是有一个奇怪的bug

它钩住鼠标，但只有在鼠标左上后移动鼠标时，才会绘制矩形

我不知道为什么。你能帮助我吗？ 谢谢

MouseHooker内部回调

private static IntPtr MyCallbackFunction(int code, UIntPtr wParam, IntPtr lParam)
    {
        // messsage not processed
        if ( code < 0 )
            SafeNativeMethods.CallNextHookEx(IntPtr.Zero,code,wParam,lParam);

        // check outside callback subscribed to delegate (NOT IMPORTANT )
        if ( state != HookState.CallBackError )
        {

            MSLLHOOKSTRUCT hk = (MSLLHOOKSTRUCT)Marshal.PtrToStructure((IntPtr)lParam, typeof(MSLLHOOKSTRUCT));
            MouseHookArgs m; // this struct only contains mouse coordinates and button
            m.x = hk.pt.x;   // clicked information
            m.y = hk.pt.y;

            // process mouse messages
            switch ((MouseMessages)wParam)
            {

              case MouseMessages.WM_MOUSEMOVE:
                  m.button = MouseButtons.M_MOVE;
                  mc(m); // call outside "callback" mc its a delegate
                break;          

                case MouseMessages.WM_LBUTTONUP:
                  m.button = MouseButtons.LB_UP;
                  mc(m);
                break;

                case MouseMessages.WM_LBUTTONDOWN:                     
                     m.button = MouseButtons.LB_DOWN;
                     mc(m);
                break;

                // more mouse message processing
         }
               // CallNextHookEx
         return SafeNativeMethods.CallNextHookEx(IntPtr.Zero,code,wParam,lParam);
}

---

如果我理解正确的话，您会说当绘制矩形时，它所绘制的位置与您单击的位置偏移

如果只是一个小数目，那么可能是舍入误差。MSLHOOKSTRUCT将pt定义为一个点，它是由两个浮点组成的结构，而不是两个整数。 （）

任何其他错误都与指针的测量位置（屏幕边缘）和绘图事件的测量位置（我们看不到，因为您没有张贴图形对象的设置位置）的差异有关

---

希望这有帮助

“老鼠屋”。。。不错；）callbackrect在何处使用以及如何使用？@Tigran主窗体包含一个带有此原型公共委托void MouseCallBack（MouseHookArgs mas）的MouseHooker委托；此委托绑定到callbackrect函数，因此在安装挂钩时，“原始”鼠标消息由MyCallBackFunction处理，callbackrect通过mc delegate调用。delegate=typesafe“pointer”指向函数可能重复的

void callbackrect( MouseHookArgs args )
    {

        switch (args.button)
        {
            case ppk.Hooks.MouseButtons.LB_UP:

                clean = true;
                ok = true;

                dest.X = args.x; // this struct its a Point
                dest.Y = args.y;

                // put destination mouse coordinate in form label
                capt.Text = string.Format("X: {0} , Y: {1}", dest.X, dest.Y);

            break;

            case ppk.Hooks.MouseButtons.LB_DOWN:                

            if ( clean )
            {                    
                clean = false;
                ok = false;
            }
                origin.X = args.x; // get origin mouse coordinate (to draw rectangle )
                origin.Y = args.y;

                // put origin mouse coordinate in form label 
                rat.Text = string.Format("X: {0} , Y: {1}", origin.X, origin.Y);

            break;    

        }

        // Invalidate & Update Desktop RECT Unmanaged because it's a efficient
        SafeNativeMethods.InvalidateRect(IntPtr.Zero, IntPtr.Zero, true);
        SafeNativeMethods.UpdateWindow(IntPtr.Zero); 

        if (ok && clean)  // Graphics g it's static and created in another location.
                          // Managed because creating a Pen, get DC, etc it's a pain
                          // and need more unmanaged code. So, why not use graphics ?                                  
            g.DrawRectangle(Pens.Red, origin.X, origin.Y, dest.X - origin.X, dest.Y - origin.Y);                                                     
    }