206 lines
7.5 KiB
HTML
206 lines
7.5 KiB
HTML
<html>
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<meta http-equiv=Content-Type content="text/html; charset=windows-1252">
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<meta name=Generator content="Microsoft FrontPage 5.0">
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<title>Portals</title>
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</head>
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<body lang=EN-US style='text-justify-trim:punctuation'>
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<div class=Section1>
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<p class=MsoNormal style='text-autospace:none'><b><font size="6">Portals</font></b></p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Portals
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divide the world into cells. Each cell is a non-solid, non-detail volume
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inside the BSP that does not cross any portals. Every non-solid part of
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the map exists in exactly one cell. Cells can have any arbitrary shape,
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such as L or cube. Portals connect two cells. The classic example is
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doorways in a house, where each room is a cell and the doorways are portals.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Whenever
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a cell is determined to be at least partially visible, all of the world
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geometry in that cell gets drawn. If a world surface exists on both sides
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of a portal, it gets drawn if either of the two cells are drawn. </p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Note:
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model bounding boxes will get clipped against the portals so they may not get
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drawn even if they are in a cell that is drawn.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Portals
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gives better culling than PVS since they effectively do the exact cell-to-cell
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PVS for a single view point. Portals can even cull geometry when you turn
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the mouse, rather than being fixed for a given point. Too many portals
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can slow the game down because it does too much time calculating what to
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draw. Portals do frustum culling of triangles, (strafe in front of a
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doorway in CoD2 with r_showtris 1 to observe this in action). Because of this it
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is not necessary to have portals inside of rooms, only at the windows and doors.
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Use r_showportals 1 in the game to see where IW placed their portals. </p>
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<p class=MsoNormal style='text-autospace:none'>Too
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few portals can slow the game down because it quickly decides to draw too much.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>You
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have to place portals in radiant for portal-based rendering. A
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portal can be any brush face; it doesn't have to be axial and it doesn't have
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to be square. To create a portal, create a brush and then make most sides
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<EFBFBD>textures / common / portalnodraw<61> and one side "textures / common /
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portal". </p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>portalnodraw
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is just like nodraw but is designed to be used with portal.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Only
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structural brushes can make up the other walls of a cell with portals. Open a
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map and filter out the patches (Alt-3), detail brushes (Ctrl-d) and entities
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(Alt-2) and observe whats left. Usually this will be just a few simple walls, the
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sky and some caulk brushes. This is what the portal render <20>sees<65>. </p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Portals
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are not allowed to have the same cell on both sides. If the compiler
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detects this, it will ignore the portal and issue a warning. This is known as a
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portal leak and it will generate a .lin file the same as a regular leak. </p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Portals
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are not allowed to have one side completely against a solid brush (partially is
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okay, including partially inside solid). If the compiler detects this, it
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will ignore the portal and issue a warning.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Portals
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are not allowed the T-junction with other portals. The portal whose face is
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touching the edge of the other perpendicular portal must have its face split
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along the edge it shares with that portal. </p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'> </span></p>
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<p class=MsoNormal style='text-autospace:none'>An
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example of placing 2 portals to cull geometry around a corner: The diagonal
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portals here each share 1 edge exactly on the inside corner of this hallway.
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Cell number 1 can not see the portal face which divides cell 2 from cell 3.
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Since it can not see this portal, it does not draw the triangles inside cell 3. </p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'> </span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>############</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># 2 /<2F><> 3</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># /</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># /########</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># / #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>#/ #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># 1 #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'> </span></p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>Another
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example. Position 4 can see through the portal into the cell where position 5
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is, however... frustum culling keeps the observer at position 4 from drawing
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the object at position 5.</p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'><EFBFBD><EFBFBD><EFBFBD><EFBFBD> 4</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'> </span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>##########-------##########</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'># <20>5<EFBFBD><35><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> #</span></p>
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<p class=MsoNormal style='text-autospace:none'>
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<span style='font-size:10.0pt;
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'>#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> #</span></p>
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<p class=MsoNormal style='text-autospace:none'> </p>
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</div>
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</body>
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</html> |