Water (shader)

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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.
Flow Mapping
Water can flow in arbitrary directions. It's very tricky to create a flow map by hand however, and the tool Valve used internally hasn't been released.

Shader parameters


Tip:There is no $basetexture, The surface is a combination of fog colour, animated bump map, reflection and refraction.
$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.
$underwateroverlay <material> (New with Source 2007)
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 The $dudvmap command is obsolete.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.


$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.
$lightmapwaterfog <bool> (New with Left 4 Dead 2)
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.


$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.
$reflect2dskybox (New with Portal 2)
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

Size/angle of $scroll1 and $scroll2
$scroll1 "[<normal X> <normal Y>]" (New with Source 2007)
$scroll2 "[<normal X> <normal Y>]" (New with Source 2007)
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.)


$flowmap  <texture>
This is a texture that defines flow velocity by skewing and scrolling the $normalmap. This effect isn't limited to the water shader, It was first used for the purple Vortigaunt warp effect seen in Episode 1 and 2. For the preservation of sanity Valve generate theirs with Houdini
L4d2 flowmap user.jpg L4d2 flowmap tex.jpg L4d2 flowmap dev.jpg
See a clip of the effect on YouTube. For a detailed description of how it all works see Alex Vlachos' SIGGRAPH 2010 paper.
$flow_normaluvscale  <float>
The number of world units covered by the normal map before it repeats. Typically in the 100s.
$flow_worlduvscale  <float>
The number of times the flow map fits into the material. Face texture scale affects this.
$flow_uvscrolldistance  <float>
How far along the flow map the normal map should be distorted. Higher values lead to more distortion.
$flow_timeintervalinseconds  <float>
Time needed for the normal map to cross the $flow_uvscrolldistance.
$flow_timescale  <float>
Modifies flow speed without affecting the amount of distortion.
$flow_bumpstrength  <normal>
How rough surface of the water is. Going above 1 is not recommended.
$flow_noise_texture  <texture>
A treatment texture used to break up repetition of the normal map.
$flow_noise_scale  <float>
How many times to fit the noise texture into the normal map. Typically around 0.01.
$flow_debug  <boolean>
Replaces the water surface with a literal rendering of the flow map.
Bug: Although the flow map will show up in Hammer, it may not be in the correct place! Don't rely on Hammer's view for alignment.

Basetexture Flow

$bastexture <texture> (New with Portal 2)
Used to create the floating debris and sludge inside test chambers.
$color_flow_uvscale  <float>
The number of world units covered by the basetexture before it repeats. Typically in the 100s.
$color_flow_timeintervalinseconds  <float>
Time needed for the normal map to cross the $color_flow_uvscrolldistance.
$color_flow_uvscrolldistance  <float>
How far along the flow map the normal map should be distorted. Higher values lead to more distortion.
$color_flow_lerpexp  <float>
How sharp the transition between repeats, should be 1.
To do: Better explanation
$color_flow_displacebynormalstrength  <float>
How much the normalmap effects the basetexture. around 0.01

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


%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