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158 lines
5.2 KiB
HTML
158 lines
5.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
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<HTML>
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<HEAD>
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<TITLE>id.sdk [Vis Portals]</title>
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<LINK REL="stylesheet" HREF="style.css">
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</HEAD>
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<BODY marginwidth="0" marginheight="0" topmargin="0" leftmargin="0">
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<table border=0 cellpadding=0 cellspacing=0 style="width: 100%; height: 99px">
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<tr>
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<td style="width: 171px"><img src="images/doom.jpg" style="width: 171px; height: 99px" alt=""></td>
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<td style="background: url(images/tile.gif)">
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<table border=0 cellpadding=0 cellspacing=0 width=600>
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<tr>
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<td style="height: 19px; background: url(images/sdk.gif) no-repeat"></td>
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<td rowspan=4 align=right><img src="images/id.gif" style="width: 42px; height: 99px" alt=""></td>
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</tr>
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<tr><td style="height: 29px; background: url(images/top.jpg) no-repeat"></td></tr>
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<tr><td style="height: 27px; background: url(images/middle.gif)" class="title"> Making DOOM 3 Mods : Vis Portals</td></tr>
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<tr><td style="height: 24px; background: url(images/bottom.jpg) no-repeat"></td></tr>
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</table>
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</td>
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</tr>
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</table>
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<table border=0 cellpadding=0 cellspacing=0 style="width: 770px">
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<tr>
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<td colspan=2 style="background: url(images/boxtop.gif);"><img src="images/span.jpg" style="width: 397px; height: 20px; float: left" alt=""></td>
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</tr>
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<tr>
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<td style="vertical-align: top; width: 152px; background: url(images/tileleft.gif)">
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<div class="leftMenu">
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<script src="menu.js"></script>
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</div>
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</td>
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<td class="mainContent">
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Here is a simple donut map 8 portals in it. When this level is compiled, it creates 8 areas. Those areas are numbered 1-8 in the screenshot below.
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<p>
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<img src="visportals/pdas_2dedit.png">
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<p>
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When Doom 3 renders the level, it first renders the area the view is in then it flows through all visible portals
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rendering each area it encounters. In this example, it would render area 3, then it would render areas 2 and 5, then areas 1 and 8,
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then maybe areas 4 and 7.
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<p>
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If a level has no vis portals in it, there is only one area so the entire level is rendered every frame.
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<p>
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The renderer determines visibility between areas by doing unions of the screen space rectangles between the areas. The following
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in-game screenshots should make that statement a little easier to understand.
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<p>
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<img src="visportals/pdas_ingame_step1.png">
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<br>
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<img src="visportals/pdas_ingame_step2.png">
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<br>
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<img src="visportals/pdas_ingame_step3.png">
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<br>
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<img src="visportals/pdas_ingame_step4.png">
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<p>
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<b>Walls</b>
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<p>
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Notice how the renderer only uses the portals for determining visibility, it does not use geometry at all. If you have a wall in between
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two portals, it will still render what's on the other side of the wall unless there is another portal in between to divide the room into
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two areas.
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<p>
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<img src="visportals/walls_dont_block1.png"><img src="visportals/walls_dont_block2.png">
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<p>
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<b>Doors</b>
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<p>
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If a vis portal is placed inside a door, the door will automatically close the portal when the door is closed. You can do the same
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thing manually through func_portal entities (these are handy for complex doors like airlocks).
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<p>
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<b>Batches</b>
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<p>
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The downside to portals is that they create extra triangles and extra batches. Video cards are set up to handle a small number of batches
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with a large number of triangles per batch. All the triangles in a single area with the same texture are put into a batch. When you create
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a vis portal, it splits the geometry, and adds more batches. This is normally not a problem unless you have a lot of areas with only a hand
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full of triangles in them.
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<p>
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<b>Testing</b>
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<p>
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To test the visibility in your own map, use the following cvars:
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<pre>
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r_showTris 2
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r_useScissor 0
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r_showPortals 1
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</pre>
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<p>
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<b>Scissors</b>
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<p>
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To further improve rendering speeds, the Doom 3 engine utilized scissors when rendering areas through a portal. These scissors prevent
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geometry outside the portal rectangle from being drawn by the video card. This is not a magic cure however, because the data is still
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being sent to the video card, it's just that the video card is ignoring it.
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<p>
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If you do not set r_useScissor 0 then you will not see the full extents of what is being rendered. You will only see what the video card is
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actually drawing. Remember, just because your video card is throwing away the geometry doesn't mean it's free. Your CPU still has to waste
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time sending the data to the video card. This is a very slow process. You don't want your computer to waste time sending a lot of data to
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the graphics card just to have it thrown away.
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<p>
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Here is the same scene with scissors enabled:
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<p>
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<img src="visportals/pdas_ingame_scissors.png">
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<p>
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<b>Remember, always test your portals with scissors disabled!</b>
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<br>
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</td>
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</tr>
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<tr>
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<td colspan=2 bgcolor="#CCCCCC"><img src="images/span2.gif" style="width: 397px; height: 8px; float: left;"></td>
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</tr>
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</table>
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<table border=0 cellpadding=0 cellspacing=0 width=770>
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<tr>
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<td align=left class="legalese">Copyright © 2004 <a href="http://www.idsoftware.com">id software</a></td>
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</tr>
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</table>
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</body>
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</html>
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