Water (shader)

Left 4 Dead 2 introduced flowing water.

Real-time reflection of entities in Episode Two.

Water is one of the Source engine's most complex shaders. It creates animated, real-time reflective & refractive, fogged, normal-mapped, and flowing water.

Special behaviour

Expensive and cheap

Water materials fall into two groups: expensive and cheap. Expensive water reflects and refracts the world in real-time, while cheap water uses an $envmap and does not refract. Users can disable expensive water rendering through their video options, so always place env_cubemaps.

Above and below

Water actually requires two materials: one for above the surface and one for below. These materials are independent of each other, but of course for proper effect need to correlate in most areas.

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Water can flow in arbitrary directions. It's very tricky to create a flow map by hand however, and the tool Valve use internally is unreleased.

Shader parameters

Textures

Tip:There is no $basetexture before Portal 2, The surface is a combination of fog colour, animated bump map, and reflection.

$abovewater <bool>

Whether this material is used for above or below the water’s surface.

$bottommaterial <material>

Required field. This is the material (not texture) to use when underneath the water’s surface. The bottom material must have $reflecttexture and $abovewater disabled, but can otherwise do whatever it wants.

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Applies a screen overlay when the camera is underwater. Generally used with effects\water_warp01. Requires $abovewater to be 0.

$bumpmap <texture>

$normalmap <texture>

A Du/dv map for DirectX 8 rendering ($bumpmap), and a bump map for DirectX 9 and above ($normalmap). These should be animated unless the water is to be perfectly still.

Note:The $normalmap command is unique to the Water shader, and uses a normal map. A du/dv map is used for $bumpmap when using the Water shader. The $dudvmap command is obsolete.

Tip:Use $bumptransform with the TextureScroll proxy to move the normal map.

$dudvframe <int>

$bumpframe <int>

Frame to start the animated du/dv map and bump map on, respectively. Somewhat confusingly, $bumpframe affects $normalmap, which should be pointing to a bump map.

Fog

$fogcolor <RGB matrix>

This is the color of the water’s volumetric fog. Generally this value should match the color used in the bottom material.

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Allows the fog to receive lightmaps, so that static objects can cast shadows onto the water. Must be enabled when the map is compiled.

$fogenable <bool>

Enable volumetric fog for the water.

$fogend <float>

This is the distance in inches from the eye at which water fog ends.

$fogstart <float>

This is the distance in inches from the eye at which water fog starts.

Warning:Must be 0 for edge fading to work properly.

Reflection/Refraction

$envmap <env_cubemap / texture>

Provides reflections for cheap water. See $envmap

$forcecheap <bool>

Make this water cheap regardless of the water_lod_control entity's or user's settings. This will disable real-time reflection and instead use $envmap. Refraction is assumed to be opaquely the water fog color.

$forceexpensive <bool>

This forces the water to render itself as expensive, regardless of the map's water_lod_control or the user's settings.

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Makes this water reflect the skybox material in addition to other reflections.

$reflectamount <float>

This is the amount of warp for the reflection. Higher values produce more visible reflections.

$reflectentities <bool>

Make the water reflect entities. By default, no entities are reflected.

$reflecttexture <texture>

Texture to use for reflection. For real-time reflections, use _rt_WaterReflection.

Tip:Specify $refracttexture without $reflecttexture to get real-time refraction on $envmap reflections.

$reflecttint <RGB matrix>

This is the color tint for the real-time reflection and environment map.

$refractamount <float>

This is the amount of warp for the refraction. Higher values produce more warping.

$refracttexture <texture>

Texture to use for refraction. For real-time refractions, use _rt_WaterRefraction.

Tip:Specify $refracttexture without $reflecttexture to get real-time refraction on $envmap reflections.

$refracttint <RGB matrix>

This is the color of the refraction.

Warning:It is recommended that you set this to white or something close to white so that edge transitions work properly on DX9.

Flowing water

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If $scroll1 is defined and X is not zero, two more instances of the normal map will be drawn in such a way that they are merged together. The first layer is 7x larger and rotated 45°; the second is 2x larger and rotated 90°. The parameters specify the speed and direction that the extra layers will move. (Valve's materials usually contain a third number, but it doesn't have any apparent effect and is most likely obsolete.)

Basetexture Flow

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Used to create the floating debris and sludge inside test chambers.

Todo: Better explanation

Authoring a flow map

Directions of water flow depend on the red and green channels of the flow map.

Overall, trying to create a flow map manually is a nightmare. Painting the flowmap, fitting it into the world, and painting foam, is extremely difficult.

But if you do want to give it a try, flow direction is read from the red and green channels of the flow map. 50% tone means no movement.

The texture scale of any faces using a water texture with a flow map appear to have a direct correlation on the flow map. The fewer water faces or planes you use the easier the process of authoring a custom flow map will be (selecting all of your water faces and using 'treat as one' when using the fit scaling may also be an option)

Red channel

X axis

Green channel

Y axis

Alpha channel

In Portal 2, Controls basetexture blend (water/sludge)

There are now tools to assist in painting flowmaps.

Flow field editor from algoholic.eu : http://algoholic.eu/another-flow-field-editor-update/

Flowmap generator (paid): http://www.superpositiongames.com/products/flowmap-generator

Creating flowmaps using Houdini (UDK) : https://www.dropbox.com/s/ii2x077vj64lyhl/Water%20Flow%20For%20UDK.pdf

Other

%compilewater <bool>

This is needed to make a map using the material compile properly.

$surfaceprop water

Tells the physics system that the surface is water. See $surfaceprop.

%tooltexture <texture>

Defines the texture Hammer will display in the material browser.

WaterLOD proxy

This connects the water_lod_control entity in a level to the water’s internal parameters. This must be declared in the material for the LOD mechanisms to work properly.

See also

• Adding Water (in Hammer)
• Creating a Waterfall Material
• Making a wall of water
• True reflections under CSS (French)