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VC++ 解決在鼠標移動時，光標閃爍的問題。其實本質是 ON_SETCURSOR的用法，vcon_setcursor

編輯：C++入門知識

VC++ 解決在鼠標移動時，光標閃爍的問題。其實本質是 ON_SETCURSOR的用法，vcon_setcursor

在調用Windows API函數SetCursor設置光標時，可能會碰到閃爍的問題：移動鼠標，光標在Class Cursor(即注冊窗口類時指定的Cursor)與預設Cursor之間閃爍。

在MSDN上有關SetCursor函數的備注中強調，如果Class Cursor非空，那麼每當鼠標移動，系統都會把光標恢復為Class Cursor。為了避免光標閃爍這一問題，必須處理WM_SETCURSOR消息。(MSDN說明)

下面是一個例子：程序在主窗口視圖的中間位置繪制RGB條帶，當鼠標移動在條帶范圍就將光標設置成為Cross，此外根據光標的位置，在RGB條帶上方30px處顯示所處條帶的顏色。程序運行起來像這樣：

如果在WM_MOUSEMOVE的消息處理中判斷光標的位置並設置光標的話，就會碰到所說的光標閃爍問題。WM_MOUSEMOVE的消息處理如下代碼所示：

01.LRESULT OnMouseMove(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)  
02.{  
03.    POINT ptCursor = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };  
04.    RECT rect, rectText;  
05.    get_rects(&rect, &rectText);  
06.    InvalidateRect(&rectText);  
07.    UpdateWindow();  
08.    if (::PtInRect(&rect, ptCursor)) {  
09.        ::SetCursor(m_cursor);  
10.        int dx = (rect.right - rect.left) / 3;  
11.        LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };  
12.        int index;  
13.        if (ptCursor.x - rect.left < dx)  
14.            index = 0;  
15.        else if (ptCursor.x - rect.left < 2 * dx)  
16.            index = 1;  
17.        else index = 2;  
18.        WTL::CString str;  
19.        str.Format(_T("Cursor on %s part"), ppsz[index]);  
20.        CClientDC dc(m_hWnd);  
21.        dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);  
22.    }  
23.    else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));  
24.    return 0;  
25.}

閃爍產生的原因在於每次進入OnMouseMove之前，系統都會先將光標恢復成Arrow，進入OnMouseMove之後，如果光標處在RGB條帶范圍內則立即被設置成Cross。

解決辦法就是將上面的判斷邏輯放在WM_SETCURSOR的消息處理中，當然獲得光標客戶坐標的方式不同，代碼如下所示：

[cpp] view plaincopyprint?
1.LRESULT OnSetCursor(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)  
2.{  
3.    POINT point;  
4.    ::GetCursorPos(&point);  
5.    ScreenToClient(&point);  
6.    set_cursor(point);  
7.    return 0;  
8.}

	LRESULT OnSetCursor(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)
	{
		POINT point;
		::GetCursorPos(&point);
		ScreenToClient(&point);
		set_cursor(point);
		return 0;
	}

而代碼中的set_cursor私有方法其實就是上面的判斷邏輯，即：

[cpp] view plaincopyprint?
1.// ptCursor: in client coordinate  
2.void set_cursor(POINT& ptCursor) throw()  
3.{  
4.    RECT rect, rectText;  
5.    get_rects(&rect, &rectText);  
6.    InvalidateRect(&rectText);  
7.    UpdateWindow();  
8.    if (::PtInRect(&rect, ptCursor)) {  
9.        ::SetCursor(m_cursor);  
10.        int dx = (rect.right - rect.left) / 3;  
11.        LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };  
12.        int index;  
13.        if (ptCursor.x - rect.left < dx)  
14.            index = 0;  
15.        else if (ptCursor.x - rect.left < 2 * dx)  
16.            index = 1;  
17.        else index = 2;  
18.        WTL::CString str;  
19.        str.Format(_T("Cursor on %s part"), ppsz[index]);  
20.        CClientDC dc(m_hWnd);  
21.        dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);  
22.    }  
23.    else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));  
24.}

	// ptCursor: in client coordinate
	void set_cursor(POINT& ptCursor) throw()
	{
		RECT rect, rectText;
		get_rects(&rect, &rectText);
		InvalidateRect(&rectText);
		UpdateWindow();
		if (::PtInRect(&rect, ptCursor)) {
			::SetCursor(m_cursor);
			int dx = (rect.right - rect.left) / 3;
			LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };
			int index;
			if (ptCursor.x - rect.left < dx)
				index = 0;
			else if (ptCursor.x - rect.left < 2 * dx)
				index = 1;
			else index = 2;
			WTL::CString str;
			str.Format(_T("Cursor on %s part"), ppsz[index]);
			CClientDC dc(m_hWnd);
			dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);
		}
		else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));
	}

這樣就解決了光標閃爍的問題。

在調用Windows API函數SetCursor設置光標時，可能會碰到閃爍的問題：移動鼠標，光標在Class Cursor(即注冊窗口類時指定的Cursor)與預設Cursor之間閃爍。

如果在WM_MOUSEMOVE的消息處理中判斷光標的位置並設置光標的話，就會碰到所說的光標閃爍問題。WM_MOUSEMOVE的消息處理如下代碼所示：

[cpp] view plaincopyprint?

LRESULT OnMouseMove(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)
{
POINT ptCursor = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };
RECT rect, rectText;
get_rects(&rect, &rectText);
InvalidateRect(&rectText);
UpdateWindow();
if (::PtInRect(&rect, ptCursor)) {
::SetCursor(m_cursor);
int dx = (rect.right - rect.left) / 3;
LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };
int index;
if (ptCursor.x - rect.left < dx)
index = 0;
else if (ptCursor.x - rect.left < 2 * dx)
index = 1;
else index = 2;
WTL::CString str;
str.Format(_T("Cursor on %s part"), ppsz[index]);
CClientDC dc(m_hWnd);
dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);
}
else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));
return 0;
}

	LRESULT OnMouseMove(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)
	{
		POINT ptCursor = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };
		RECT rect, rectText;
		get_rects(&rect, &rectText);
		InvalidateRect(&rectText);
		UpdateWindow();
		if (::PtInRect(&rect, ptCursor)) {
			::SetCursor(m_cursor);
			int dx = (rect.right - rect.left) / 3;
			LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };
			int index;
			if (ptCursor.x - rect.left < dx)
				index = 0;
			else if (ptCursor.x - rect.left < 2 * dx)
				index = 1;
			else index = 2;
			WTL::CString str;
			str.Format(_T("Cursor on %s part"), ppsz[index]);
			CClientDC dc(m_hWnd);
			dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);
		}
		else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));
		return 0;
	}

閃爍產生的原因在於每次進入OnMouseMove之前，系統都會先將光標恢復成Arrow，進入OnMouseMove之後，如果光標處在RGB條帶范圍內則立即被設置成Cross。

解決辦法就是將上面的判斷邏輯放在WM_SETCURSOR的消息處理中，當然獲得光標客戶坐標的方式不同，代碼如下所示：

[cpp] view plaincopyprint?

LRESULT OnSetCursor(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)
{
POINT point;
::GetCursorPos(&point);
ScreenToClient(&point);
set_cursor(point);
return 0;
}

	LRESULT OnSetCursor(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM lParam, BOOL& /*bHandled*/)
	{
		POINT point;
		::GetCursorPos(&point);
		ScreenToClient(&point);
		set_cursor(point);
		return 0;
	}

而代碼中的set_cursor私有方法其實就是上面的判斷邏輯，即：

[cpp] view plaincopyprint?

// ptCursor: in client coordinate
void set_cursor(POINT& ptCursor) throw()
{
RECT rect, rectText;
get_rects(&rect, &rectText);
InvalidateRect(&rectText);
UpdateWindow();
if (::PtInRect(&rect, ptCursor)) {
::SetCursor(m_cursor);
int dx = (rect.right - rect.left) / 3;
LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };
int index;
if (ptCursor.x - rect.left < dx)
index = 0;
else if (ptCursor.x - rect.left < 2 * dx)
index = 1;
else index = 2;
WTL::CString str;
str.Format(_T("Cursor on %s part"), ppsz[index]);
CClientDC dc(m_hWnd);
dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);
}
else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));
}

	// ptCursor: in client coordinate
	void set_cursor(POINT& ptCursor) throw()
	{
		RECT rect, rectText;
		get_rects(&rect, &rectText);
		InvalidateRect(&rectText);
		UpdateWindow();
		if (::PtInRect(&rect, ptCursor)) {
			::SetCursor(m_cursor);
			int dx = (rect.right - rect.left) / 3;
			LPTSTR ppsz[] = { _T("Red"), _T("Green"), _T("Blue") };
			int index;
			if (ptCursor.x - rect.left < dx)
				index = 0;
			else if (ptCursor.x - rect.left < 2 * dx)
				index = 1;
			else index = 2;
			WTL::CString str;
			str.Format(_T("Cursor on %s part"), ppsz[index]);
			CClientDC dc(m_hWnd);
			dc.DrawText(str, -1, &rectText, DT_CENTER | DT_VCENTER);
		}
		else ::SetCursor(CCursor().LoadSysCursor(IDC_ARROW));
	}

這樣就解決了光標閃爍的問題。