Question

C++怎么获取指定窗口句柄某点像素值

C++初学，比如我打开了很多窗口，但我想得到其中一个窗口里某点的像素值，可以得到这个窗口句柄。

Answer 1

#include <atlbase.h>
#include <atlwin.h>

typedef CWinTraits<WS_SYSMENU | WS_VISIBLE | WS_CLIPCHILDREN | WS_CLIPSIBLINGS , WS_EX_TOOLWINDOW> FrameWinTraits; 

class CMainFrame : public CWindowImpl<CMainFrame, CWindow,FrameWinTraits> {
public:
	BEGIN_MSG_MAP(CMainFrame)
		MESSAGE_HANDLER(WM_CLOSE, OnClose)
		MESSAGE_HANDLER(WM_ERASEBKGND, OnEraseBkgnd)
		MESSAGE_HANDLER(WM_PAINT, OnPaint)
		MESSAGE_HANDLER(WM_LBUTTONDOWN, OnLButtonDown)
		MESSAGE_HANDLER(WM_LBUTTONUP, OnLButtonUp)
		MESSAGE_HANDLER(WM_MOUSEMOVE, OnMouseMove)
	END_MSG_MAP()
public:
	CMainFrame() : m_clr(0xFFFFFF) {} 
private:
	LRESULT OnClose(UINT, WPARAM, LPARAM, BOOL&) 
	{
		PostMessage(WM_QUIT); 
		return 0; 
	}

	LRESULT OnEraseBkgnd(UINT, WPARAM, LPARAM, BOOL&) 
	{
		return 1; 
	}

	LRESULT OnPaint(UINT, WPARAM, LPARAM, BOOL&) 
	{
		RECT rc; 
		PAINTSTRUCT ps; 

		GetClientRect(&rc); 
		HDC hDC = ::BeginPaint(m_hWnd, &ps); 
		COLORREF clrOld = ::SetBkColor(hDC, m_clr);
	 	if(clrOld != CLR_INVALID)
		{
			ExtTextOut(hDC, 0, 0, ETO_OPAQUE, &rc, NULL, 0, NULL);
			DrawText(hDC, _T("按下鼠标左键移动鼠标获取颜色"), -1, &rc, DT_CENTER | DT_VCENTER | DT_WORDBREAK ); 
			SetBkColor(hDC, clrOld);
		}
		::EndPaint(m_hWnd, &ps);
		return 0; 
	}
	
	LRESULT OnLButtonDown(UINT, WPARAM, LPARAM lParam, BOOL& bHandled)
	{
		::SetCapture(m_hWnd); 
		return 0; 
	}
	
	LRESULT OnLButtonUp(UINT, WPARAM, LPARAM, BOOL& bHandled) 
	{
		::ReleaseCapture(); 
		return 0; 
	}

	LRESULT OnMouseMove(UINT, WPARAM, LPARAM lParam, BOOL& bHandled) {
		POINT pt = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) }; 
		ClientToScreen(&pt); 
		HWND hWnd = WindowFromPoint(pt); 
		if (m_hWnd != hWnd) {
			HDC hDC = ::GetWindowDC(hWnd); 
			COLORREF clr = GetPixel(hDC, pt.x, pt.y);
			::ReleaseDC(hWnd, hDC); 
			if (clr != m_clr) {
				m_clr = clr; 
				InvalidateRect(NULL); 
			}
		}
		return 0; 
	}
private:
	COLORREF m_clr; 
};

int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
 	DefWindowProc(NULL, 0, 0, 0L);
   
 	RECT rc = {0,0,200,100};
	CMainFrame wndFrame;
	wndFrame.Create(NULL,&rc);
	wndFrame.CenterWindow();
	wndFrame.ShowWindow(SW_SHOW);
 
 	MSG msg;
 	while (GetMessage(&msg, NULL, 0, 0)) {
		TranslateMessage(&msg);
		DispatchMessage(&msg);
 	}
	wndFrame.DestroyWindow();
  	return 0;
}

获取颜色部分在OnMouseMove() 方法中

代码 VC8 测试通过， 测试方法：创建一个空工程，然后添加一个CPP, 直接复制代码后编译即可直接运行

Answer 2

windows API 句柄。参考windows api函数手册有详解