Water in SRB2 is a type of floor over floor. To create water, you need to make both a control sector outside the map and a sector inside the map where the water will appear. The ceiling of the control sector is the surface of the water, and the floor is the bottom. If you're going to create rivers, lakes or pools, the water block itself should be put inside a pit, because if the floor is placed above the floor of the target sector, the water will end up as a literal block of water floating in air. If the Repeat Midtexture flag is checked on the control linedef, it will generate a water ripple on the surface of the water.
The texture used for the control linedef is the texture used on the side of the block. Use a waterfall texture here and the edge of the block will look like falling water. Place another water block next to it at a lower level to create a waterfall. If you're not using the waterfall feature, it's a good idea to use the "No Sides" water types to make it slightly faster to render.
Current linedef types available for water FOFs (the links below contain sample WADs and complete info on how to make water FOFs):
- Linedef type 120: FOF: Water, Opaque
- Linedef type 121: FOF: Water, Translucent
- Linedef type 122: FOF: Water, Opaque, No Sides
- Linedef type 123: FOF: Water, Translucent, No Sides
- Linedef type 124: FOF: Goo Water, Translucent
- Linedef type 125: FOF: Goo Water, Translucent, No Sides
An important point in making water blocks is to use a Colormap. Make a new control sector and select a linedef. Set the control linedef's upper texture to #40A0FFJ. Tag the control linedef to the water's control sector. The colormap is what causes the greenish-blue tint when the player is underwater.
Liquids other than water are made simply by changing the textures and colormap. If the liquid is painful, apply the damage sector effect to the water's control sector.
- Goo water – Use linedef type 124 or linedef type 125 for the goo physics. The official SRB2 maps use #CF7FCFZ for the colormap.
- Lava – Apply Damage (Fire) for the fire damage. An appropriate colormap color would be #FF7F00Z. Unlike other liquids, put #FF7F00Z on both the upper and lower texture of the colormap control linedef to create the fog effect inside the lava.
- Old THZ slime – Damage (Water) is used for slime damage. The old SRB2 maps used #E000E0S for the colormap, but #FF00FFS is also a good option.