ArcBall Camera

[source lang "cpp"]D3DXVECTOR3 Camera::PlotMouseToBall(){	GetCursorPos(&cursor_current_pos);	D3DXVECTOR3 rp;        // ViewPort is just the client area of the window	rp.x = ((cursor_current_pos.x - 108) / (float)(ViewPort.x>>1)) - 1.0f;	rp.y = ((cursor_current_pos.y - 154) / (float)(ViewPort.y>>1)) - 1.0f;	float z = 1.0f - (MXMATH::sqr(rp.x) + MXMATH::sqr(rp.y));	if(z >= 0)		rp.z = sqrt(z);	else		rp.z = 0.0f;	return rp;}void Camera::CalculateBallRotation(){	D3DXVECTOR3 nowPoint = PlotMouseToBall();	if(spherePoint == nowPoint)	{		BALL_angle += 0;		is_changed = true;	}	else	{	D3DXVec3Normalize(&nowPoint, &nowPoint);	D3DXVec3Normalize(&spherePoint, &spherePoint);	if(TODEG(BALL_angle) >= 360)		BALL_angle -= TORAD(360);	BALL_angle += MXMATH::AngleBetweenVectors(spherePoint, nowPoint);	D3DXVec3Cross(&BALL_axis, &nowPoint, &spherePoint);	D3DXVec3Normalize(&BALL_axis, &BALL_axis);	spherePoint = nowPoint;	is_changed = true;	}	}// and then I call D3DXMatrixRotationAxis() and set that matrix as the world transformation matrix.CameraPerspective.BuildWorldTrackBallMatrix(&g_mx_view, g_device);g_device->SetTransform(D3DTS_WORLD, &g_mx_transform);