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C#+Windows : マウスフックとSendInputを使ってマウスLボタン離したときのY座標をドラッグ開始時の座標に置換してきれいな横線を引かせる

やりたいこと

横線をひくアシストをする。
マウスドラッグ中のアシストはせず、ボタンを離したときの位置を調整する。

基本アイデア

マウスのボタンを離したときのY座標を、ドラッグ開始時の座標に置換することで、Y方向のぶれを0にし、完全に水平な線を引かせる。

ソースコード

※マウスフックとSendInputの影響のせいか、本プログラムに対する終了操作を受け付けなくなる場合があります。

変換式はちょっと問題ありです。 https://qiita.com/kob58im/items/23df9e22778b33986d1c 参照。


using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

class MainForm : Form
{
    bool dragingNow;
    int dragStartX;
    int dragStartY;
    //TextBox txt;

    MainForm()
    {
        Text = "MouseHooker";
        ClientSize = new System.Drawing.Size(700,200);
        Shown += (s,e)=>{Start();};
        FormClosed += (s,e)=>{Stop();};

        //txt = new TextBox();
        //Controls.Add(txt);

        dragingNow = false;
    }

    [STAThread]
    static void Main(string[] args)
    {
        NativeMethods.SetProcessDPIAware(); // 高解像度のスケーリング座標に対応するため
        Application.Run(new MainForm());
    }



    private static class NativeMethods
    {
        public delegate IntPtr MouseHookCallback(int nCode, uint msg, ref MSLLHOOKSTRUCT msllhookstruct);

        [DllImport("user32.dll")]
        public static extern System.IntPtr SetWindowsHookEx(int idHook, MouseHookCallback lpfn, IntPtr hMod, uint dwThreadId);

        [DllImport("user32.dll")]
        public static extern System.IntPtr CallNextHookEx(IntPtr hhk, int nCode, uint msg, ref MSLLHOOKSTRUCT msllhookstruct);

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool UnhookWindowsHookEx(IntPtr hhk);


        [DllImport("user32.dll", SetLastError = true)]
        public extern static void SendInput(int nInputs, Input[] pInputs, int cbsize);

        [DllImport("user32.dll", SetLastError = true)]
        public extern static IntPtr GetMessageExtraInfo();

        [DllImport( "user32.dll" )]
        public static extern bool SetProcessDPIAware();
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int x;
        public int y;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct MSLLHOOKSTRUCT
    {
        public POINT pt;
        public uint mouseData;
        public uint flags;
        public uint time;
        public IntPtr dwExtraInfo;
    }

    private const int WH_MOUSE_LL = 14;
    private const int WM_MOUSEMOVE   = 0x0200;
    private const int WM_LBUTTONDOWN = 0x0201;
    private const int WM_LBUTTONUP   = 0x0202;
    private const int WM_RBUTTONDOWN = 0x0204;



    private IntPtr hookHandle;
    private event NativeMethods.MouseHookCallback hookCallback;

    public void Start()
    {
        hookCallback = HookProcedure;
        hookHandle = NativeMethods.SetWindowsHookEx(WH_MOUSE_LL, hookCallback, IntPtr.Zero, 0);

        if (hookHandle == IntPtr.Zero)
        {
            throw new System.ComponentModel.Win32Exception();
        }
    }

    public void Stop()
    {
        if (hookHandle != IntPtr.Zero)
        {
            NativeMethods.UnhookWindowsHookEx(hookHandle);
            hookHandle = IntPtr.Zero;
        }
    }

    // 注意:このメソッド内で時間のかかる処理をすると、しばらくフリーズしてフックが外れてしまいます。
    //       SendInputを直接呼ぶと、しにます。(おそらく、イベントのバッファが壊れておかしくなる?)
    private IntPtr HookProcedure(int nCode, uint msg, ref MSLLHOOKSTRUCT s)
    {
        if ( nCode >= 0 )
        {
            txt.Text = msg.ToString()+"]"+(s.pt.x).ToString();

            if ( msg == WM_LBUTTONDOWN )
            {
                dragingNow = true;
                dragStartX = s.pt.x;
                dragStartY = s.pt.y;
            }
            else if ( msg == WM_LBUTTONUP )
            {
                if (dragingNow) {
                    dragingNow = false;
                    int absDx = s.pt.x - dragStartX;
                    int absDy = s.pt.y - dragStartY;
                    if ( absDx < 0 ) { absDx = -absDx; }
                    if ( absDy < 0 ) { absDy = -absDy; }
                    if ( absDy < absDx/2 ) {
                        int x = s.pt.x;
                        BeginInvoke((MethodInvoker)delegate(){SendInputMouseLButtonUp(x, dragStartY);});
                        return (IntPtr)1;   // cancel
                    }
                }
            }
        }

        return NativeMethods.CallNextHookEx(hookHandle, nCode, msg, ref s);
    }



    [StructLayout(LayoutKind.Sequential)]
    struct MouseInput
    {
        public int X;
        public int Y;
        public int Data;
        public int Flags;
        public int Time;
        public IntPtr ExtraInfo;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct KeyboardInput
    {
        public short VirtualKey;
        public short ScanCode;
        public int Flags;
        public int Time;
        public IntPtr ExtraInfo;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct HardwareInput
    {
        public int uMsg;
        public short wParamL;
        public short wParamH;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct Input
    {
        public int Type;
        public InputUnion ui;
    }

    [StructLayout(LayoutKind.Explicit)]
    struct InputUnion
    {
        [FieldOffset(0)]
        public MouseInput Mouse;
        [FieldOffset(0)]
        public KeyboardInput Keyboard;
        [FieldOffset(0)]
        public HardwareInput Hardware;
    }

    private const int MOUSEEVENTF_MOVE        = 0x0001;
    private const int MOUSEEVENTF_LEFTDOWN    = 0x0002;
    private const int MOUSEEVENTF_LEFTUP      = 0x0004;
    private const int MOUSEEVENTF_VIRTUALDESK = 0x4000;
    private const int MOUSEEVENTF_ABSOLUTE    = 0x8000;

    private static void SendInputMouseLButtonUp(int x, int y)
    {
        if (x<0) {x=0;}
        if (y<0) {y=0;}
        x = (int)( (x*(long)65535) / (Screen.PrimaryScreen.Bounds.Width -1) ); // 微妙に変換があっていないっぽい。分母を-1しない場合でもずれる
        y = (int)( (y*(long)65535) / (Screen.PrimaryScreen.Bounds.Height-1) );
        SendInputMouseLButtonUpAbs(x, y);
    }

    private static void SendInputMouseLButtonUpAbs(int absX, int absY)
    {
        var stepMouseUp = new Input();
        stepMouseUp.Type = 0; // MOUSE = 0
        stepMouseUp.ui.Mouse.X = absX;
        stepMouseUp.ui.Mouse.Y = absY;
        stepMouseUp.ui.Mouse.Data = 0;
        stepMouseUp.ui.Mouse.Flags = MOUSEEVENTF_ABSOLUTE | MOUSEEVENTF_MOVE | MOUSEEVENTF_LEFTUP;
        stepMouseUp.ui.Mouse.Time = 0;
        stepMouseUp.ui.Mouse.ExtraInfo = IntPtr.Zero;

        Input[] inputs = new Input[]{stepMouseUp};
        NativeMethods.SendInput(inputs.Length, inputs, Marshal.SizeOf(inputs[0]));
    }
}

はまりがちな罠たち

・SendInputで使うInput構造体のPacking C# SendInputによるマウス操作の落とし穴 - 64bitの罠
・フック内でSendInputを直接コールしてはいけない(フリーズする)
・フック内でConsole.WriteLineすると、ときどき短時間フリーズしてフックが外れる(タイムアウトっぽい)
・高解像度によるマウスフックの座標系のずれ Windowsのフックのはまりどころ備忘録
・SendInputのAbsolute座標への変換式... 整数除算なので丸目誤差に注意。そもそも、まだ式が合っていない説ある

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