C#使用PrintWindow進行窗口抓圖

本文和C++使用PrintWindow進行窗口抓圖對應，使用C#實現。

Win32封裝同C#使用BitBlt進行窗口抓圖。

這種方式對1920*1080大小的窗口，一次抓圖的時間參考（VS2015+i5 9400F）：20~30ms（平均23ms）。

參見：C#抓圖服務。

PrintCaptureHelper.cs

using System;

namespace CaptureSharp
{
    internal class PrintCaptureHelper
    {
        public IntPtr BitmapPtr => _hBitmap;
        public Win32Types.BitmapInfo BitmapInfo { get; } = new Win32Types.BitmapInfo();
        public Win32Types.Rect WindowRect => _windowRect;
        public Win32Types.Rect ClientRect => _clientRect;
        public int BitmapDataSize => _bmpDataSize;

        private IntPtr _hWnd = IntPtr.Zero;
        private IntPtr _hScrDc = IntPtr.Zero;
        private IntPtr _hMemDc = IntPtr.Zero;
        private IntPtr _hBitmap = IntPtr.Zero;
        private IntPtr _hOldBitmap = IntPtr.Zero;

        private Win32Types.Rect _windowRect;
        private Win32Types.Rect _clientRect;
        private int _bmpDataSize;

        public bool Init(IntPtr handle)
        {
            _hWnd = handle;

            //獲取窗口大小
            if (!Win32Funcs.GetWindowRect(_hWnd, out _windowRect) ||
                !Win32Funcs.GetClientRect(_hWnd, out _clientRect))
            {
                return false;
            }

            _bmpDataSize = _windowRect.Width * _windowRect.Height * 3;

            _hScrDc = Win32Funcs.GetWindowDC(_hWnd);
            _hBitmap = Win32Funcs.CreateCompatibleBitmap(_hScrDc, _windowRect.Width, _windowRect.Height);
            _hMemDc = Win32Funcs.CreateCompatibleDC(_hScrDc);
            _hOldBitmap = Win32Funcs.SelectObject(_hMemDc, _hBitmap);

            return true;
        }

        public bool Init(string windowName)
        {
            var handle = Win32Funcs.FindWindow(null, windowName);
            if (handle.Equals(IntPtr.Zero))
            {
                return false;
            }

            return Init(handle);
        }

        public void Cleanup()
        {
            if (_hBitmap.Equals(IntPtr.Zero))
            {
                return;
            }

            //刪除用過的對象
            Win32Funcs.SelectObject(_hMemDc, _hOldBitmap);
            Win32Funcs.DeleteObject(_hBitmap);
            Win32Funcs.DeleteDC(_hMemDc);
            Win32Funcs.ReleaseDC(_hWnd, _hScrDc);

            _hWnd = IntPtr.Zero;
            _hScrDc = IntPtr.Zero;
            _hMemDc = IntPtr.Zero;
            _hBitmap = IntPtr.Zero;
            _hOldBitmap = IntPtr.Zero;
        }

        public bool RefreshWindow()
        {
            return ChangeWindowHandle(_hWnd);
        }

        public bool ChangeWindowHandle(string windowName)
        {
            Cleanup();
            return Init(windowName);
        }

        public bool ChangeWindowHandle(IntPtr handle)
        {
            Cleanup();
            return Init(handle);
        }

        public IntPtr Capture()
        {
            if (_hMemDc.Equals(IntPtr.Zero) || _hScrDc.Equals(IntPtr.Zero))
            {
                return IntPtr.Zero;
            }

            var ret = Win32Funcs.PrintWindow(_hWnd, _hMemDc,
                (uint) Win32Consts.PrintWindowMode.PW_CLIENTONLY |
                (uint) Win32Consts.PrintWindowMode.PW_RENDERFULLCONTENT);
            return ret ? _hBitmap : IntPtr.Zero;
        }

        public bool Capture(out IntPtr bitsPtr, out int bufferSize, out Win32Types.Rect rect)
        {
            bitsPtr = _hBitmap;
            bufferSize = _bmpDataSize;
            rect = _clientRect;

            if (_hBitmap.Equals(IntPtr.Zero) || _hMemDc.Equals(IntPtr.Zero) || _hScrDc.Equals(IntPtr.Zero))
            {
                return false;
            }

            var ret = Win32Funcs.PrintWindow(_hWnd, _hMemDc,
                (uint) Win32Consts.PrintWindowMode.PW_CLIENTONLY |
                (uint) Win32Consts.PrintWindowMode.PW_RENDERFULLCONTENT);

            return ret;
        }
    }
}