Note: if you've never used BSP before, I suggest that you review some of my General BSP tutorials to get a feel for using the editor. These tutorials for Quake-specific items will be geared to people who are already comfortable with BSP.

Remember when I told you that all Quake brushes were solid? Well, that's true except for 3 cases: Water, Lava and Slime. These are the only types of brushes that the player can actually be inside (for a brief period anyway). This lesson will show you how to use create these liquid brushes. It's really not hard, so this will be a fairly short lesson. Be sure you have a map file from a previous lesson available. If you don't have one, you can use this file.

Liquid Brushes are created in the same way as normal brushes. They become liquid when you assign a liquid texture to them. In the QUAKE101.wad file, the liquid textures are: *LAVA1, *LAVA2, *SLIME1, *SLIME2, *WATER0, *WATER1, *WATER2. There is also a *WATER3 texture available in Quake, but for some reason it's not included in QUAKE101.wad. Simply by applying one of these textures to a brush, you make it liquid. Pretty easy, huh? Actually, the *TELEPORT texture is treated as a liquid texture by Quake also; just in case you were wondering...

Let's add a pit to our map and I'll show you how to make a liquid brush. Easy as it is, there are a couple of things to look out for. Start out in the Top View and draw a new brush from (-832, -64) to (-448, -192). Switch to the Front View and drag the bottom of your brush to -80 on the Z axis. Drag the top of the brush to 8. Now since we want to make a hole in the floor for our pit, subtract this brush from the world, but don't delete it.

Once you've subtracted the brush, drag the top of this new brush down so that it is level with the floor of the room (0 on the Z axis). While it's still selected, let's go ahead and apply a texture to this brush. I've chosen 'WALL3_4' for a texture. That way when we make this brush into a pit, it will look like it was dug out of the rock under our room. Select the top face of the brush and apply 'FLOOR01_5' to the top face only. That way it will blend in with the rest of the floor.

Now let's hollow out our pit. In the Top view, draw a new brush from (-824, -72) to (-456, -184). Switch to the Front view again and set the top of the brush at 8 and the bottom at -72. Once you've gotten the brush positioned correctly, go ahead and subtract it, but again, don't delete it. After the brush is subtracted, drag the top edge down to -8 and apply '*LAVA1' for a texture.

We're ready to compile our map. Go ahead and compile your map and run it in Quake. Here's what you should see:

Of course, you can make a slime brush the same way we just made our lava brush; just select one of the slime textures instead of the one we used. We could do that here, but let's change the texture to '*WATER0' instead. That will make our pit into a swimming pool. Go ahead and change the texture on this brush and while we're at it, let's add a light down in the water, so we can see where we're swimming. Make a couple of light entities (I gave mine a 150 value) and space them throughout the water. Now, recompile your map and take a look. This time it looks a little more inviting:

There are two views: One from above and one from underwater. Notice that the floor texture of the room is also the floor of our pit. This is because it was the texture of the top face of the brush we used to carve the pit. It carried over to this brush automatically.

All right, now remember in the last lesson, we learned how to use the 'trigger_push' entity to make a wind tunnel? Well, we can use this same entity to make a current in our pit. This would be great to simulate an underground river. Let's do that now. In the Top view, draw a brush from (-816, -80) to (-464, -176). In the Front view, set the top of the brush at -64 and the bottom at -72. Now make this entity into a 'trigger_push' entity. Set the angle to 180 and assign a key/value pair of 'speed' '7'. That's pretty slow, but we don't want the player to be shooting the rapids after all do we? Any faster and the player can't move against the current. As it is, the player can move, but it's a struggle.

Re-compile your map and jump into the pit. The current will carry you across the room, but you can swim against the current if you want. When you're done playing, jump out of the water to leave the pit. Pretty cool!

Well that wraps up this lesson. See, I told you this would be a short one. Before we finish up, though, there is one more thing you need to know about liquid brushes. As you know in Quake, you can set the texture of each face on a brush individually. However, this doesn't apply to liquid brushes. They must have all faces the same texture or QBSP will generate an error and your map won't compile. If you ever see a message complaining about 'mixed faces' in QBSP, this is probably the cause.