屏幕截图程序（WTL）

如果需要思路，请访问：http://hi.baidu.com/sumos/item/9aef19f4f02e0f5ac9f337bb

如果需要程序，请访问：http://download.csdn.net/detail/zhoujielunzhimi/4724327

如果需要源码，请看：

#pragma once
#include <atlimage.h>

class MainForm;

CBitmap bmp_srcreen;	//用来保存全屏图片
MainForm *mf_ptr = NULL;

//截屏窗口
class ScreenForm : public CWindowImpl<ScreenForm>
{
public:
	ScreenForm() : is_lbutton_down(false){}
protected:
	BEGIN_MSG_MAP(ScreenForm)
		MSG_WM_CREATE(OnCreate)
		MESSAGE_HANDLER(WM_KEYDOWN,OnKeyDown)
		MSG_WM_RBUTTONDOWN(OnRButtonDown)
		MSG_WM_SETCURSOR(OnSetCursor)
		MSG_WM_LBUTTONDOWN(OnLButtonDown)
		MSG_WM_MOUSEMOVE(OnMouseMove)
		MSG_WM_LBUTTONUP(OnLButtonUp)
		MSG_WM_ERASEBKGND(OnEraseBkgnd)
		MSG_WM_PAINT(OnPaint)
	END_MSG_MAP()
protected:
	int OnCreate(LPCREATESTRUCT)
	{
		CRect rc(0,0,0,0);
		SetWindowPos(HWND_TOPMOST,&rc,SWP_NOMOVE|SWP_NOSIZE);	//置顶
		return 0;
	}
	LRESULT OnKeyDown(UINT,WPARAM wp,LPARAM,BOOL&)
	{
		if(wp == VK_LWIN || wp == VK_RWIN || VK_ESCAPE)	//左WIN + 右WIN + ESC
			OnRButtonDown(0,CPoint(0,0));
		return 0;
	}
	void OnRButtonDown(UINT nFlags, CPoint point)
	{
		DestroyWindow();
		((CWindowImpl*)mf_ptr)->ShowWindow(SW_SHOW);
	}
	BOOL OnSetCursor(CWindow wnd, UINT nHitTest, UINT message)
	{
		static CCursor cursor = AtlLoadCursor(IDC_CURSOR1);  //载入光标资源：十 字形状
		::SetCursor(cursor);
		return TRUE;
	}
	void OnLButtonDown(UINT nFlags, CPoint point)
	{
		is_lbutton_down = true;
		pt_old = point;
	}
	void OnMouseMove(UINT nFlags, CPoint point)
	{
		pt_end = point;
		Invalidate();	
	}
	void OnLButtonUp(UINT nFlags, CPoint point)
	{
		is_lbutton_down = false;
		int ret = MessageBox("复制到剪贴板(OK)或保存为PNG图片(CANCEL)？","ASK",MB_OKCANCEL|MB_ICONQUESTION);

		CDC dc1,dc2;
		dc1.CreateCompatibleDC(NULL);
		dc1.SelectBitmap(bmp_srcreen);
		CRect rc(pt_old.x,pt_old.y,pt_end.x,pt_end.y);
		dc2.CreateCompatibleDC(dc1);
		CBitmap bmp;	//dc1选择了全屏图片，dc2选择了截图区域
		bmp.CreateCompatibleBitmap(dc1,rc.Width(),rc.Height());
		dc2.SelectBitmap(bmp);
		dc2.BitBlt(0,0,rc.Width(),rc.Height(),dc1,pt_old.x,pt_old.y,SRCCOPY);
		if(ret == IDOK)
		{
			if(OpenClipboard())	//复制到剪贴板
			{
				::EmptyClipboard();
				::SetClipboardData(CF_BITMAP,bmp);
				::CloseClipboard();
			}
		}
		else
		{
			CImage img;
			img.Attach(bmp);
			img.Save("catch.png");	//保存为png，因为保存为bmp图片太大了
			img.Detach();
		}

		OnRButtonDown(0,CPoint(0,0));
	}
	BOOL OnEraseBkgnd(CDCHandle dc)
	{		
		return TRUE;
	}
	void OnPaint(CDCHandle)
	{
		CPaintDC dc(m_hWnd);

		CRect rc;
		GetClientRect(&rc);

		CMemoryDC mem(dc,rc);	//WTL提供的双缓存，析构时自动绘制

		CBrush br;
		br.CreateSolidBrush(RGB(255,255,255));

		mem.FillRect(&rc,br);	//把窗口底色刷白

		if(bmp_srcreen.IsNull())
			return;

		CDC dcMem;
		dcMem.CreateCompatibleDC(mem);
		dcMem.SelectBitmap(bmp_srcreen);

		BLENDFUNCTION bf;
		bf.AlphaFormat = 0;
		bf.BlendFlags = 0;
		bf.BlendOp = AC_SRC_OVER;
		bf.SourceConstantAlpha = 100;
		//绘制半透明的全屏图像，类似win7自带的截图软件
		mem.AlphaBlend(0,0,rc.Width(),rc.Height(),dcMem,0,0,rc.Width(),rc.Height(),bf);

		if(is_lbutton_down)
		{
			CRect rc_catch(pt_old.x,pt_old.y,pt_end.x,pt_end.y);
			//不透明的显示选择区域图像
			mem.BitBlt(pt_old.x,pt_old.y,rc_catch.Width(),rc_catch.Height(),dcMem,pt_old.x,pt_old.y,SRCCOPY);
			mem.Draw3dRect(&rc_catch,RGB(255,0,0),RGB(0,0,255));
		}
	}
private:
	CPoint pt_old;
	CPoint pt_end;
	bool is_lbutton_down;	
};

//主窗口
class MainForm : public CWindowImpl<MainForm>
{
protected:
	BEGIN_MSG_MAP(MainForm)
		MSG_WM_CLOSE(OnClose)
		MSG_WM_ERASEBKGND(OnEraseBkgnd)
		COMMAND_CODE_HANDLER(BN_CLICKED,OnClick)
	END_MSG_MAP()
protected:
	void OnClose()
	{
		DestroyWindow();
		::PostMessage(NULL,WM_QUIT,0,0);
	}
	BOOL OnEraseBkgnd(CDCHandle dc)  //这不过是为主窗口加个背景图罢了
	{
		CRect rc;
		GetClientRect(&rc);
		CBitmap bk;
		bk.LoadBitmap(IDB_BITMAP1);
		CDC mem;
		mem.CreateCompatibleDC(dc);
		mem.SelectBitmap(bk);
		BITMAP bkInf;
		bk.GetBitmap(&bkInf);
		dc.StretchBlt(0,0,rc.Width(),rc.Height(),mem,0,0,bkInf.bmWidth,bkInf.bmHeight,SRCCOPY);
		return TRUE;
	}
	LRESULT OnClick(WORD,WORD id,HWND,BOOL&)
	{
		CRect rc;
		switch(id)
		{
		case IDC_CREATE :
			ShowWindow(SW_HIDE);
			Sleep(300);		//需要等待一下，否则会把主窗口图像也捕捉下来
			{
				//捕捉屏幕
				CRect rcDesk;
				CWindow wndDesk = ::GetDesktopWindow();
				wndDesk.GetClientRect(&rcDesk);
				rc = rcDesk;
				CDCHandle dcDesk = wndDesk.GetDC();
				CDC dcMem;
				dcMem.CreateCompatibleDC(dcDesk);
				if(bmp_srcreen.IsNull() == FALSE)
					bmp_srcreen.DeleteObject();
				bmp_srcreen.CreateCompatibleBitmap(dcDesk,rcDesk.Width(),rcDesk.Height());
				dcMem.SelectBitmap(bmp_srcreen);
				dcMem.BitBlt(0,0,rcDesk.Width(),rcDesk.Height(),dcDesk,0,0,SRCCOPY);
				wndDesk.ReleaseDC(dcDesk);
			}
			sf.Create(m_hWnd,rc,NULL,WS_VISIBLE|WS_POPUP);
			break;
		default:
			break;
		}
		return 0;
	}
public:
	void InitForm()
	{
		font_btn.CreatePointFont(110,"宋体");
		// 400 * 300
		btn_create.Create(m_hWnd,CRect(20,10,120,40),"新建",WS_VISIBLE|WS_CHILD|BS_PUSHBUTTON,0,IDC_CREATE);
		btn_create.SetFont(font_btn);
	}
private:
	CButton btn_create;		
	CFont font_btn;
	ScreenForm sf;

	enum { IDC_CREATE = 10001 };
};

截图中：背景是半透明，选中区域是不透明。