View source for CFuncMoveLinear ParentingFix

The issue is that two parts of {{ent|func_movelinear}}'s code use {{ent|GetAbsOrigin()}}, the position relative to the world, instead of {{ent|GetLocalOrigin()}}, the position relative to the world ''or parent''. All of these changes are done in <code>func_movelinear.cpp</code> and <code>func_movelinear.h</code>.

The first offender is this bit of code in <code>Spawn()</code>:
<source lang=cpp>
	m_vecPosition1 = GetAbsOrigin() - (m_vecMoveDir * m_flMoveDistance * m_flStartPosition);
	m_vecPosition2 = m_vecPosition1 + (m_vecMoveDir * m_flMoveDistance);
	m_vecFinalDest = GetAbsOrigin();
</source>

Replace that with this code:
<source lang=cpp>
	m_vecPosition1 = GetLocalOrigin() - (m_vecMoveDir * m_flMoveDistance * m_flStartPosition);
	m_vecPosition2 = m_vecPosition1 + (m_vecMoveDir * m_flMoveDistance);
	m_vecFinalDest = GetLocalOrigin();
	m_vecReference = GetLocalOrigin();
</source>

Notice the usage of <code>m_vecReference</code>. That will be declared later in the article.

The other offender is <code>MoveDone()</code>:
<source lang=cpp>
	if ( GetAbsOrigin() == m_vecPosition2 )
	{
		m_OnFullyOpen.FireOutput( this, this );
	}
	else if ( GetAbsOrigin() == m_vecPosition1 )
	{
		m_OnFullyClosed.FireOutput( this, this );
	}
</source>

Replace that with this code:
<source lang=cpp>
	if ( GetLocalOrigin() == m_vecPosition2 )
	{
		m_OnFullyOpen.FireOutput( this, this );
	}
	else if ( GetLocalOrigin() == m_vecPosition1 )
	{
		m_OnFullyClosed.FireOutput( this, this );
	}
</source>

Even though the usage of <code>GetAbsOrigin()</code> is the main problem and the entity should now work properly when used with the <code>parentname</code> keyvalue, the entity may still stop working properly if <code>SetParent</code> or <code>ClearParent</code> are used, as the position the end points are relative to isn't actually saved and is lost when being re/unparented, causing inconsistencies with the <code>func_movelinear</code>'s end points.

First, add this to <code>func_movelinear.h</code>, perhaps under the declaration of <code>ShouldSavePhysics()</code>.
<source lang=cpp>
void		SetParent( CBaseEntity* pNewParent, int iAttachment = -1 );
</source>

In the same file, add these lines under the declaration of <code>m_flMoveDistance</code>:
<source lang=cpp>
	// For the parenting fix.
	// Prevents position inconsistencies when changing parent.
	Vector		m_vecReference;
</source>

Now, in <code>func_movelinear.cpp</code>, add this definition to the entity's <code>DATADESC</code>, preferably under <code>m_flMoveDistance</code>:
<source lang=cpp>
	DEFINE_FIELD( m_vecReference, FIELD_VECTOR ),
</source>

That <code>m_vecReference</code> variable was used earlier in the article as part of <code>Spawn()</code>. It saves the place where the <code>func_movelinear</code> started for when the entity is parented to something else, which ensures the end points are transferred correctly.

Now, let's add that <code>SetParent()</code> we declared:
<source lang=cpp>
//-----------------------------------------------------------------------------
// Purpose: Sets the movement parent of this entity. This entity will be moved
//			to a local coordinate calculated from its current absolute offset
//			from the parent entity and will then follow the parent entity.
// Input  : pParentEntity - This entity's new parent in the movement hierarchy.
//-----------------------------------------------------------------------------
void CFuncMoveLinear::SetParent( CBaseEntity *pParentEntity, int iAttachment )
{
	Vector oldLocal = GetLocalOrigin();

	BaseClass::SetParent( pParentEntity, iAttachment );

	// SOLID_NONE indicates we haven't spawned yet
	if (GetSolid() != SOLID_NONE)
	{
		m_vecReference = ((m_vecReference - oldLocal) + GetLocalOrigin());
		m_vecPosition1 = m_vecReference - (m_vecMoveDir * m_flMoveDistance * m_flStartPosition);
		m_vecPosition2 = m_vecPosition1 + (m_vecMoveDir * m_flMoveDistance);
		m_vecFinalDest = m_vecReference - m_vecFinalDest;
	}
}
</source>

That should be everything to get <code>func_movelinear</code> to work while parented.

== Conclusion ==
This is an improved and more lightweight version of a [https://developer.valvesoftware.com/w/index.php?title=CFuncMoveLinear_ParentingFix&oldid=218480 previous fix] which used two different endpoint entities. The current fix was originally developed for {{Game link|Mapbase}}.

Please keep an eye out for any problems, as this was mostly just tested on one map with a bunch of {{ent|ent_fire}} usage.

[[Category:Free source code|F]]