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A '''visleaf''', or merely a leaf, is one of many visleafs &mdash;think of them as sections&mdash; in which a map is divided during the compiling process. Each leaf is a volume that contains a section of geometry that is drawn together. When '''any''' part of a leaf is visible from the current leaf, all of the geometry in the leaf is considered for rendering by the engine. You can view the current leaf in the engine by typing <code>mat_leafvis 1</code> at the developer console. A red wireframe box will be drawn showing the current leaf. As you move around in the level, the box will redraw each time a new leaf is entered. Another way of visualizing leaves is to use the [[glview]] (<code>glview.exe</code>) command-line tool.
A '''visleaf''', or merely a leaf, is one of many visleaves &mdash;think of them as sections&mdash; in which a map is divided during the compiling process. Each leaf is a volume that contains a section of geometry that is drawn together. When '''any''' part of a leaf is visible from the current leaf, '''all of the geometry in the leaf is considered for rendering by the engine'''. Calculating which leaves can see which is a large portion of [[|Vvis|VVIS]]' purpose.


=How are leafs created?=
You can view the current leaf in the engine by typing <code>mat_leafvis 1</code> at the developer console. A red wireframe box will be drawn showing the current leaf. As you move around in the level, the box will redraw each time a new leaf is entered. Another way of visualizing visleaves is to use the [[glview]] (<code>glview.exe</code>) command-line tool.


First, we'll take a look at an example level. We have a level with a few rooms in it:
==See also==


[[Image:Room1.JPG | an example map]]
*[[Optimization (Geometry)#Visibility]]
*[[Controlling Geometry Visibility and Compile Times]]


This level is run through [[vbsp|VBSP]] (<code>vbsp.exe</code>) and it will divide the level into leafs. Each leaf starts, and ends at a plane where a brush begins. Like below:
[[Image:Room2.JPG | another example map]]
Leafs, just like brushes, can't be [[concave]]. They can have any size (up to 1024 units, more on that later) and shape, as long as it's not concave.
Notice how there are no entities in this room. I left them out to illustrate leafs are in no way affected by entities, not even brush-based entities, or [[displacement]]s. That's exactly why tieing brushes to entities reduces visleafs: the less brushes in your level, the less leafs have to be made. If in our example all the middle walls wouldn't exist, we would only have one visleaf in our level.
{{Note|If your map has leaks, VBSP will not be able to divide your level into leafs. For more information, see [[leak]].}}
{{Note|VBSP always cuts your level up along the center lines (as shown by the two green lines in the editor) and every 1024 units (as shown by red-brown lines). If you look very careful in the first pics, you can see a green center line cutting through the middle of the red leaf, so in reality this leaf would be cut in two, not that that would have changed anything for our example though.}}
When your leaves are made, VBSP will write their data into a portalfile (<code>mapname.prt</code>).
Now, once our map is cut up into leafs, [[vvis|VVis]] (<code>vvis.exe</code>) will do it's job: It will read the portalfile made by VBSP into it's memory and it will try to figure out which leafs can see which ones. In our example, VVis would create a table like below:
# green can see blue and red
# blue can see green and red
# red can see all other leafs
# yellow can see purple and red
# purple can see yellow and red
If VVis can draw a straight line from one leaf to the other, the leafs are thought to see each other. This line can pass everything, apart from world-brushes.
All this data is stored into the mapfile, ready to be used by the game. Note that this process may take very long, if your map has a lot of leafs. Therefore, it's best to keep the amount of leafs as low as possible, yet still effective. One big leaf in your level would be low, but not effective: The entire map would be drawn at the same time.
So, what did we gain?
Well, you can see in the list above, that apart from the red leaf, all other leafs have been optimized: The engine will not render the entire game when the player is in those leafs.
If you ever want to cut up leafs at certain planes, be sure to read up on hinting using hint brushes. Careful planning on the placement of leafs can increase the speed of your map enormously, which is explained in detail in the [[Hint brush]] article.


[[Category:Level Design]]
[[Category:Level Design]]
[[Category:Glossary]]
[[Category:Glossary]]

Revision as of 11:03, 4 January 2008

A visleaf, or merely a leaf, is one of many visleaves —think of them as sections— in which a map is divided during the compiling process. Each leaf is a volume that contains a section of geometry that is drawn together. When any part of a leaf is visible from the current leaf, all of the geometry in the leaf is considered for rendering by the engine. Calculating which leaves can see which is a large portion of [[|Vvis|VVIS]]' purpose.

You can view the current leaf in the engine by typing mat_leafvis 1 at the developer console. A red wireframe box will be drawn showing the current leaf. As you move around in the level, the box will redraw each time a new leaf is entered. Another way of visualizing visleaves is to use the glview (glview.exe) command-line tool.

See also

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