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 and refractive, fogged, normal-mapped 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 here. The surface is a combination of fog colour, animated bump map, and reflection.

Note:When using Portal 2 or Alien Swarm you can actually provide a $basetexture as it is used in Portal 2.

$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 The $dudvmap command is obsolete.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.

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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.)

$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.

Flow

Authoring a flow map

Overall, trying to create a flow map manually is a nightmare. Just working out what colours to paint is hard, and then either it's very difficult to align with the world correctly or you have to worry about seams between brushes. It's just about possible to get flow in a line (fit the water texture to each brush and rotate it to handle curves), but anything complex is out of the question.

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 blending between different water materials (water/sludge etc)

You can also use flow field editor from algoholic.eu website : http://algoholic.eu/another-flow-field-editor-update/

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)