Used MouseKeys accessibility function to show the mouse cursor

on a secondary screen when there's no physical mouse attached to
the system.  Kinda flaky when a mouse is attached or detached but
seems to work well enough when the device is not attached to start
with and not attached while running synergy.

lib/platform/CMSWindowsScreen.cpp

@@ -106,7 +106,9 @@ CMSWindowsScreen::CMSWindowsScreen(bool isPrimary,
 	m_setMode(NULL),
 	m_keyState(NULL),
 	m_suspend(suspend),
-	m_resume(resume)
+	m_resume(resume),
+	m_hasMouse(GetSystemMetrics(SM_MOUSEPRESENT) != 0),
+	m_showingMouse(false)
 {
 	assert(s_instance != NULL);
 	assert(s_screen   == NULL);
@@ -125,6 +127,7 @@ CMSWindowsScreen::CMSWindowsScreen(bool isPrimary,
 		updateScreenShape();
 		m_class       = createWindowClass();
 		m_window      = createWindow(m_class, "Synergy");
+		forceShowCursor();
 		LOG((CLOG_DEBUG "screen shape: %d,%d %dx%d %s", m_x, m_y, m_w, m_h, m_multimon ? "(multi-monitor)" : ""));
 		LOG((CLOG_DEBUG "window is 0x%08x", m_window));
 	}
@@ -240,6 +243,7 @@ CMSWindowsScreen::disable()
 	m_nextClipboardWindow = NULL;
 
 	m_isOnScreen = m_isPrimary;
+	forceShowCursor();
 }
 
 void
@@ -259,6 +263,7 @@ CMSWindowsScreen::enter()
 
 	// now on screen
 	m_isOnScreen = true;
+	forceShowCursor();
 }
 
 bool
@@ -292,6 +297,7 @@ CMSWindowsScreen::leave()
 
 	// now off screen
 	m_isOnScreen = false;
+	forceShowCursor();
 
 	return true;
 }
@@ -525,6 +531,36 @@ CMSWindowsScreen::updateKeys()
 	m_desks->updateKeys();
 }
 
+void
+CMSWindowsScreen::fakeKeyDown(KeyID id, KeyModifierMask mask,
+				KeyButton button)
+{
+	CPlatformScreen::fakeKeyDown(id, mask, button);
+	updateForceShowCursor();
+}
+
+void
+CMSWindowsScreen::fakeKeyRepeat(KeyID id, KeyModifierMask mask,
+				SInt32 count, KeyButton button)
+{
+	CPlatformScreen::fakeKeyRepeat(id, mask, count, button);
+	updateForceShowCursor();
+}
+
+void
+CMSWindowsScreen::fakeKeyUp(KeyButton button)
+{
+	CPlatformScreen::fakeKeyUp(button);
+	updateForceShowCursor();
+}
+
+void
+CMSWindowsScreen::fakeToggle(KeyModifierMask modifier)
+{
+	CPlatformScreen::fakeToggle(modifier);
+	updateForceShowCursor();
+}
+
 HINSTANCE
 CMSWindowsScreen::openHookLibrary(const char* name)
 {
@@ -829,6 +865,16 @@ CMSWindowsScreen::onEvent(HWND, UINT msg,
 		}
 		*result = TRUE;
 		return true;
+
+	case WM_DEVICECHANGE:
+		forceShowCursor();
+		break;
+
+	case WM_SETTINGCHANGE:
+		if (wParam == SPI_SETMOUSEKEYS) {
+			forceShowCursor();
+		}
+		break;
 	}
 
 	return false;
@@ -1377,6 +1423,60 @@ CMSWindowsScreen::updateKeysCB(void*)
 	updateButtons();
 }
 
+void
+CMSWindowsScreen::forceShowCursor()
+{
+	// check for mouse
+	m_hasMouse = (GetSystemMetrics(SM_MOUSEPRESENT) != 0);
+
+	// decide if we should show the mouse
+	bool showMouse = (!m_hasMouse && !m_isPrimary && m_isOnScreen);
+
+	// show/hide the mouse
+	if (showMouse != m_showingMouse) {
+		if (showMouse) {
+			m_oldMouseKeys.cbSize = sizeof(m_oldMouseKeys);
+			m_gotOldMouseKeys =
+				(SystemParametersInfo(SPI_GETMOUSEKEYS,
+							m_oldMouseKeys.cbSize,	&m_oldMouseKeys, 0) != 0);
+			if (m_gotOldMouseKeys) {
+				m_mouseKeys    = m_oldMouseKeys;
+				m_showingMouse = true;
+				updateForceShowCursor();
+			}
+		}
+		else {
+			if (m_gotOldMouseKeys) {
+				SystemParametersInfo(SPI_SETMOUSEKEYS,
+							m_oldMouseKeys.cbSize,
+							&m_oldMouseKeys, SPIF_SENDCHANGE);
+				m_showingMouse = false;
+			}
+		}
+	}
+}
+
+void
+CMSWindowsScreen::updateForceShowCursor()
+{
+	DWORD oldFlags = m_mouseKeys.dwFlags;
+
+	// turn on MouseKeys
+	m_mouseKeys.dwFlags = MKF_AVAILABLE | MKF_MOUSEKEYSON;
+
+	// make sure MouseKeys is active in whatever state the NumLock is
+	// not currently in.
+	if ((m_keyState->getActiveModifiers() & KeyModifierNumLock) != 0) {
+		m_mouseKeys.dwFlags |= MKF_REPLACENUMBERS;
+	}
+
+	// update MouseKeys
+	if (oldFlags != m_mouseKeys.dwFlags) {
+		SystemParametersInfo(SPI_SETMOUSEKEYS,
+							m_mouseKeys.cbSize, &m_mouseKeys, SPIF_SENDCHANGE);
+	}
+}
+
 LRESULT CALLBACK
 CMSWindowsScreen::wndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {

lib/platform/CMSWindowsScreen.h

@@ -80,6 +80,12 @@ public:
 
 	// IKeyState overrides
 	virtual void		updateKeys();
+	virtual void		fakeKeyDown(KeyID id, KeyModifierMask mask,
+							KeyButton button);
+	virtual void		fakeKeyRepeat(KeyID id, KeyModifierMask mask,
+							SInt32 count, KeyButton button);
+	virtual void		fakeKeyUp(KeyButton button);
+	virtual void		fakeToggle(KeyModifierMask modifier);
 
 	// IPlatformScreen overrides
 	virtual void		enable();
@@ -174,6 +180,16 @@ private:
 	// job to update the key state
 	void				updateKeysCB(void*);
 
+	// determine whether the mouse is hidden by the system and force
+	// it to be displayed if user has entered this secondary screen.
+	void				forceShowCursor();
+
+	// forceShowCursor uses MouseKeys to show the cursor.  since we
+	// don't actually want MouseKeys behavior we have to make sure
+	// it applies when NumLock is in whatever state it's not in now.
+	// this method does that.
+	void				updateForceShowCursor();
+
 	// our window proc
 	static LRESULT CALLBACK wndProc(HWND, UINT, WPARAM, LPARAM);
 
@@ -250,6 +266,23 @@ private:
 	IJob*				m_suspend;
 	IJob*				m_resume;
 
+	// the system shows the mouse cursor when an internal display count
+	// is >= 0.  this count is maintained per application but there's
+	// apparently a system wide count added to the application's count.
+	// this system count is 0 if there's a mouse attached to the system
+	// and -1 otherwise.  the MouseKeys accessibility feature can modify
+	// this system count by making the system appear to have a mouse.
+	//
+	// m_hasMouse is true iff there's a mouse attached to the system or
+	// MouseKeys is simulating one.  we track this so we can force the
+	// cursor to be displayed when the user has entered this screen.
+	// m_showingMouse is true when we're doing that.
+	bool				m_hasMouse;
+	bool				m_showingMouse;
+	bool				m_gotOldMouseKeys;
+	MOUSEKEYS			m_mouseKeys;
+	MOUSEKEYS			m_oldMouseKeys;
+
 	static CMSWindowsScreen*	s_screen;
 };