Crystal Space: 4.10.11 Portal Container Mesh Object

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### 4.10.11 Portal Container Mesh Object

Written by Jorrit Tyberghein, (jorrit.tyberghein@gmail.com).

This is a special type of mesh object which basically represents a collection of portals. The portal container is not implemented as a seperate plugin but is built-in into the engine plugin. There is no type or factory interface for portal containers. They are created by the engine directly as mesh objects.

#### Object State Interface

``iPortalContainer'` (residing in ``CS/include/iengine/portalcontainer.h'`) is the SCF interface that you can use to manipulate settings for a portal container. By using this interface you can access the portals contained in this portal container.

To create a portal container you need to use API calls in the engine: `iEngine::CreatePortalContainer()` and `iEngine::CreatePortal()`. Portal containers are normal mesh objects otherwise. They implement `iMeshObject` and are put in a sector like other mesh objects.

#### Object Loader

With normal mesh objects you have a specific loader plugin to load the mesh. Portal containers are loaded by the standard map loader instead. There are two basic ways to add a portal container to a sector. Either you use ``portals'` to define multiple portals at once (in one portal container) or else you use a single ``portal'` statement to create a portal container with one portal. In both cases you place it in a sector (it becomes a normal mesh object). In the case of ``portals'` you can also add many regular mesh object statement like ``move'` to move the portal and others. Here is an example:

    <portals name="myPortal">
      <portal>
        <v x="0.2" y="2.8" z="-0.8" />
        <v x="0.2" y="2.8" z="0.8" />
        <v x="0.2" y="-1" z="0.8" />
        <v x="0.2" y="-1" z="-0.8" />
        <sector>destSector</sector>
        <float />
        <clip />
      </portal>
      <hardmove>
        <v x="13" y="0" z="12" />
      </hardmove>
      <priority>object</priority>
    </portals>

Here you see how a portal container with a single portal is created. The destination sector is ``destSector'`.

When you use the short-hand ``portal'` statement you can't set mesh parameters like the position of the portal (you'll have to encode position in the vertices) and render priority.

Here is a list of all the tags supported by a portal object and their meaning (these tags are for usage inside the ``portal'` statement and not directly inside ``portals'`):

- ``sector'` The name of the destination sector for this portal.
- ``autoresolve'` With this flag set (default) the portal will automatically connect to the sector as soon as it is created. That means you can create a portal to a sector that doesn't yet exist. As soon as the sector is created it will connect to it. If the sector is then removed again the portal will become a ``null-portal'` again. With this flag not set you can also create a portal that will connect to a sector as soon as it is created but it will not be able to reconnect later if the sectors goes away and is created again. i.e. connection is one-time only.
- ``key'` Add a key-value item to this portal container.
- ``v'` Add a vertex to the portal polygon.
- ``maxvisit'` If you use space-warping portals it is easy to get in a situation where you have infinite recursion (i.e. imagine two mirroring portals facing each other). To avoid this problem there is a maximum recursion limit per portal. By default this is set to 5. You can change this value here.
- ``matrix'` If you use this then the portal will be a space warping portal. That means that it will change the camera transform. Using this you can do various tricks like mirrors and othes.
- ``wv'` This vector is added to the camera transform before the matrix is applied. It enables space warping.
- ``ww'` This vector is added to the camera transform after the matrix is applied. It enables space warping.
- ``mirror'` This is a shortcut to enable a space warping camera that mirrors space (like a mirror would work).
- ``clipstraddling'` With this flag set the portal will clip geometry of an object that is straddling this portal (i.e. the object is both in the source and destination sector and the portal 'cuts' the object). This is only needed if the portal is on a surface that is transparent. A space warping portal will have the effect of this flag automatically.
- ``clip'` If this flag is set then this portal will clip all geometry in the destination sector. This must be used for portals which arrive in the middle of a sector. Otherwise objects that are in the destination sector and are between the camera and the position of where the portal is in the source sector might be rendered in front of the portal incorrectly.
- ``zfill'` With this flag set the portal will do a Z-fill after rendering the contents (as if it was a normal polygon). this is mainly useful for floating portals where it is possible that there is geometry in the same sector that will be rendered behind the portal (and thus could accidently get written in the portal sector because the Z-buffer cannot be trusted).
- ``float'` If this flag is used then the portal will use possible available stencil buffer hardware to do good clipping. This flag should be used if you have a portal that is not at the boundary of a sector (i.e. there can be geometry behind the portal but in the same source sector as the portal) and that can be covered (or itself covers) other objects. It is usually used in combination with ``zfill'` and sometimes with ``clip'` if the destination of the portal enters in the middle of a sector.
- ``colldet'` If this flag is set then this portal is used for collision detection.
- ``viscull'` If this flag is set then this portal can be used for visibility culling (i.e. it acts as an occluder for objects behind the portal but in the same sector as the portal itself).
- ``static'` This flag indicates if the destination of this portal should not be transformed from object to world space. For mirrors you should disable this flag because you want the destination to move with the source.

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