C++ 使用PrintWindow实现窗口截图功能

本文使用C++双缓存进行指定窗口截图。CreateDIBSection创建应用程序可以直接写入的、与设备无关的位图(DIB)，它提供内存中位图的指针，外部程序可以直接使用。

需要注意的是，PrintWindow方法能够抓取使用D3D渲染的窗口（例如Excel、Win10自带视频播放器），如果抓取普通窗口则会附带窗口阴影，可见窗口阴影是Windows使用D3D渲染出来的。

1、PrintCaptureHelper.h

#pragma once

#include <windows.h>
#include <string>
using std::string;

class PrintCaptureHelper
{
public:
  PrintCaptureHelper();
  virtual ~PrintCaptureHelper();

  bool Init(const string& windowName);
  bool Init(HWND hwnd);
  void Cleanup();
  bool RefreshWindow();
  bool ChangeWindowHandle(const string& windowName);
  bool ChangeWindowHandle(HWND hwnd);
  bool Capture() const;

  const RECT& GetWindowRect() const { return windowRect_; }
  const RECT& GetClientRect() const { return clientRect_; }
  int GetBitmapDataSize() const { return bmpDataSize_; }
  HBITMAP GetBitmap() const { return bitmap_; }
  void* GetBitmapAddress() const { return bitsPtr_; }

private:
  HWND hwnd_;
  HDC scrDc_;
  HDC memDc_;
  HBITMAP bitmap_;
  HBITMAP oldBitmap_;
  void* bitsPtr_;

  RECT windowRect_;
  RECT clientRect_;
  int bmpDataSize_;
};

2、PrintCaptureHelper.cpp

#include "stdafx.h"
#include "PrintCaptureHelper.h"

PrintCaptureHelper::PrintCaptureHelper()
  : hwnd_(nullptr)
  , scrDc_(nullptr)
  , memDc_(nullptr)
  , bitmap_(nullptr)
  , oldBitmap_(nullptr)
  , bitsPtr_(nullptr)
  , windowRect_{ 0, 0, 0, 0 }
  , clientRect_{ 0, 0, 0, 0 }
  , bmpDataSize_(0)
{

}

PrintCaptureHelper::~PrintCaptureHelper()
{
  Cleanup();
}

bool PrintCaptureHelper::Init(const string& windowName)
{
  const auto handle = ::FindWindowA(nullptr, windowName.c_str());
  if (handle == nullptr)
  {
    return false;
  }

  return Init(handle);
}

bool PrintCaptureHelper::Init(HWND hwnd)
{
  hwnd_ = hwnd;

  //获取窗口大小
  if (!::GetWindowRect(hwnd_, &windowRect_) || !::GetClientRect(hwnd_, &clientRect_))
  {
    return false;
  }

  const auto clientRectWidth = clientRect_.right - clientRect_.left;
  const auto clientRectHeight = clientRect_.bottom - clientRect_.top;
  bmpDataSize_ = clientRectWidth * clientRectHeight * 4;

  //位图信息
  BITMAPINFO bitmapInfo;
  bitmapInfo.bmiHeader.biSize = sizeof(bitmapInfo);
  bitmapInfo.bmiHeader.biWidth = clientRectWidth;
  bitmapInfo.bmiHeader.biHeight = clientRectHeight;
  bitmapInfo.bmiHeader.biPlanes = 1;
  bitmapInfo.bmiHeader.biBitCount = 32;
  bitmapInfo.bmiHeader.biSizeImage = clientRectWidth * clientRectHeight;
  bitmapInfo.bmiHeader.biCompression = BI_RGB;

  scrDc_ = ::GetWindowDC(hwnd_);
  memDc_ = ::CreateCompatibleDC(scrDc_);
  bitmap_ = ::CreateDIBSection(scrDc_, &bitmapInfo, DIB_RGB_COLORS, &bitsPtr_, nullptr, 0);
  if (bitmap_ == nullptr)
  {
    ::DeleteDC(memDc_);
    ::ReleaseDC(hwnd_, scrDc_);
    return false;
  }

  oldBitmap_ = static_cast<HBITMAP>(::SelectObject(memDc_, bitmap_));
  return true;
}

void PrintCaptureHelper::Cleanup()
{
  if (bitmap_ == nullptr)
  {
    return;
  }

  //删除用过的对象
  ::SelectObject(memDc_, oldBitmap_);
  ::DeleteObject(bitmap_);
  ::DeleteDC(memDc_);
  ::ReleaseDC(hwnd_, scrDc_);

  hwnd_ = nullptr;
  scrDc_ = nullptr;
  memDc_ = nullptr;
  bitmap_ = nullptr;
  oldBitmap_ = nullptr;
}

bool PrintCaptureHelper::RefreshWindow()
{
  const auto hwnd = hwnd_;
  Cleanup();
  return Init(hwnd);
}

bool PrintCaptureHelper::ChangeWindowHandle(const string& windowName)
{
  Cleanup();
  return Init(windowName);
}

bool PrintCaptureHelper::ChangeWindowHandle(HWND hwnd)
{
  Cleanup();
  return Init(hwnd);
}

bool PrintCaptureHelper::Capture() const
{
  if (bitmap_ == nullptr || memDc_ == nullptr || scrDc_ == nullptr)
  {
    return false;
  }

  const auto ret = ::PrintWindow(hwnd_, memDc_, PW_CLIENTONLY | PW_RENDERFULLCONTENT);
  return ret != 0;
}

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