Water

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Water reflecting entities in real-time in Episode Two.

Water is a material shader available in all Source games. It creates water that realistically reflects and refracts the world, and that can flow throughout a map.

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

Textures

Note:In games before <Alien Swarm>, there is no $basetexture. The surface is a combination of fog color, animated bump map, reflection and refraction.
$abovewater <boolean>
Whether this material is used for above or below the water’s surface.
$bottommaterial <material>
Required parameter. This is the material (not texture) to use when underneath the water’s surface. The bottom material must have $reflecttexture, $abovewater and $envmap disabled, but can otherwise do whatever it wants.
$underwateroverlay <material> (New with Half-Life 2: Episode Two / Source 2007)
Applies a refracting screen overlay when the camera is underwater. Generally used with effects\water_warp01. Requires $abovewater to be 0.
$bumpmap <texture> (DX8)
$normalmap <texture>
A Du/dv map for DirectX 8 rendering ($bumpmap), and a bump map for DirectX 9 and above ($normalmap). These should be animated unless the water is to be perfectly still or you're using a flowmap, which makes an animated bump map redundant.
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 The $dudvmap command is obsolete.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 in pre-2006 engine branches.
$dudvframe <integer>
$bumpframe <integer>
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.
$bumptransform <matrix>
Transforms the bump map texture.
The default position is "center .5 .5 scale 1 1 rotate 0 translate 0 0".
  1. center defines the point of rotation. Only useful if rotate is being used.
  2. scale fits the texture into the material the given number of times. '2 1' is a 50% scale in the X axis.
  3. rotate rotates the texture counter-clockwise in degrees. Accepts any number, including negatives.
  4. translate shifts the texture by the given numbers. '.5' will shift it half-way.
Note:All values must be included!
Bug: Scaling the texture may cause odd issues where the Texture Lock tool in Hammer will not actually lock the texture in place.
Bug: Rotating textures applied on brushes will rotate around the map origin (confirm: Orangebox engine only?). A fix for this is to change the center position in the VMT to the brush's origin.
$scale <vector2>
To do: What does this do?
$flashlighttint <float> (New with Left 4 Dead 2)
Confirm:How much projected textures should tint the water?
$waterdepth <float> (New with Counter-Strike: Global Offensive)
To do: What does this do exactly? Seems like it's related to $waterblendfactor, Found in liquids/nuke_water.vmt. Found in 2006/2007 code, does it do anything there?
$depth_feather <integer> (New with Counter-Strike: Global Offensive)
To do: What does this do exactly? Found in liquids/nuke_water.vmt.

Fog

$fogcolor <RGB matrix>
Color of the water’s volumetric fog. Generally this value should match the color used in the bottom material.
$fogenable <boolean>
Enable volumetric fog for the water.
$fogstart <float>
Distance in inches from the eye at which water fog starts.
Warning: Must be 0 for edge fading to work properly.
$fogend <float>
Distance in inches from the eye at which water fog ends.
$lightmapwaterfog <boolean> (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.

Reflection

$reflecttexture <texture>
Texture to use for reflection. For real-time reflections, use _rt_WaterReflection.
$envmap <[[env_cubemap / texture]]>
See $envmap. Provides reflections for cheap water.
Note:Don't use this on underwater materials.
$envmapframe <integer>
The frame to start an animated cubemap on.
$forceenvmap <boolean> (New with Portal 2)
Forces the water to use $envmap for reflections.
$forcecheap <boolean>
Force the water to render itself as cheap, regardless of the map's water_lod_control entity settings or the user's settings. This will disable real-time reflection and instead use $envmap. Refraction is assumed to be opaquely the water fog color.
$forceexpensive <boolean>
Force the water to render itself as expensive, regardless of the map's water_lod_control entity settings or the user's settings.
$cheapwaterstartdistance <float>
Distance from the eye in inches that the shader should start transitioning to a cheaper water shader.
$cheapwaterenddistance <float>
Distance from the eye in inches that the shader should finish transitioning to a cheaper water shader.
$reflectskyboxonly <boolean> (New with Left 4 Dead 2)
Make the water reflect only the skybox.
$reflect2dskybox <boolean> (New with Portal 2)
Make the water reflect the skybox material in addition to other reflections.
$reflect3dskybox <boolean> (New with Counter-Strike: Global Offensive)
Make the water reflect the 3D skybox in addition to other reflections. Added in the Danger Zone update and used on dz_blacksite.
Note:Requires a sky_camera entity to be placed in the map, otherwise this might cause crashes.
$reflectentities <boolean>
Make the water reflect entities. By default, no entities are reflected.
$reflectonlymarkedentities <boolean> (New with Portal 2)
Make the water reflect only entities and static props with "Render in Fast Reflections" enabled.
$reflectamount <float>
Amount of warp for the reflection. Higher values produce more visible reflections.
$reflecttint <RGB matrix>
Color tint for the real-time reflection and environment map.
$reflectblendfactor <float>
To do: What does this do?
$nofresnel <boolean> (New with Half-Life 2: Episode One / Source 2006)
Disable the fresnel on the water's reflection.
Bug: Does not do anything in any engine branch.
$forcefresnel <float> (New with Alien Swarm)
Force this amount of fresnel on the water. Higher values usually cause the water to appear brighter.
Bug: Does not work properly in <Insurgency><Day of Infamy>.
$basereflectance <float>
To do: What is this?
$maxreflectance <float>
To do: What is this?

Refraction

$refract <boolean> (New with Left 4 Dead 2)
Whether the material should refract at all.
$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.
$refractamount <float>
Amount of warp for the refraction. Higher values produce more warping.
$refracttint <RGB matrix>
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.
$blurrefract <boolean> (New with Half-Life 2: Episode Two / Source 2007) (DX9+)
Blurs the refraction when underwater.
Warning: Underwater materials only; this will cause buggy behavior on any material with $abovewater set to 1.
$pseudotranslucent <boolean> (New with Portal 2)
Make the water translucent. This is a cheap substitute for refractive water; do not use this when refraction is enabled.
$waterblendfactor <normal> (New with Portal 2)
How translucent the water should be when $pseudotranslucent is enabled. At 0, the water is completely transparent, while at 1 the water is completely opaque.
Size/angle of $scroll1 and $scroll2

Flowing water

$scroll1 "[<normal X> <normal Y>]" (New with Half-Life 2: Episode One / Source 2006)
$scroll2 "[<normal X> <normal Y>]" (New with Half-Life 2: Episode One / Source 2006)
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.)

Flowmaps

A flowmap texture.
The flowmap texture in-engine, shown with $flow_debug 1.
The result in-engine.
$flowmap <texture> (New with Left 4 Dead 2)
Texture that defines flow velocity by skewing and scrolling the $normalmap. Valve generates their flowmaps with Houdini.
Video of the effect. For technical details, see Alex Vlachos' SIGGRAPH 2010 paper and Valve's GDC 2011 paper.
$flow_normaluvscale <float> (New with Left 4 Dead 2)
The number of world units covered by the normal map before it repeats. Typically in the 100s.
$flow_worlduvscale <float> (New with Left 4 Dead 2)
The number of times the flow map fits into the material. Face texture scale affects this.
$flow_uvscrolldistance <float> (New with Left 4 Dead 2)
How far along the flow map the normal map should be distorted. Higher values lead to more distortion.
$flow_timeintervalinseconds <float> (New with Left 4 Dead 2)
Time needed for the normal map to cross the $flow_uvscrolldistance.
$flow_timescale <float> (New with Left 4 Dead 2)
Modifies flow speed without affecting the amount of distortion.
$flow_bumpstrength <normal> (New with Left 4 Dead 2)
How rough the surface of the water is.
$flow_noise_texture <texture> (New with Left 4 Dead 2)
A treatment texture used to break up repetition of the normal map.
$flow_noise_scale <float> (New with Left 4 Dead 2)
How many times to fit the noise texture into the normal map. Typically around 0.01.
$flow_debug <boolean> (New with Left 4 Dead 2)
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

$basetexture <texture> (New with Alien Swarm)
A "sludge layer", used in [Portal 2] for the sludge and debris in test chambers. The alpha channel of the $basetexture acts as a mask for the reflection; darker values are more reflective, while lighter values are less reflective.
Note:From [Portal 2] onwards, the opacity of the $basetexture is controlled by the alpha channel of the flowmap.
$color_flow_uvscale <float> (New with Alien Swarm)
The number of world units covered by the base texture before it repeats. Typically in the 100s.
$color_flow_timescale <float> (New with Alien Swarm)
Modifies flow speed without affecting the amount of distortion.
$color_flow_timeintervalinseconds <float> (New with Alien Swarm)
Time needed for the base texture to cross the $color_flow_uvscrolldistance.
$color_flow_uvscrolldistance <float> (New with Alien Swarm)
How far along the flow map the base texture should be distorted. Higher values lead to more distortion.
$color_flow_lerpexp <float> (New with Alien Swarm)
How sharp the transition should be between repeats, should be 1.
To do: Better explanation
$color_flow_displacebynormalstrength <float> (New with Portal 2)
How much the normal map affects the base texture. Uses extremely low values, usually 0.01 or less.

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
Controls $basetexture blend from [Portal 2] onwards.
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 <boolean>
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