Water (shader)

Water reflecting entities in real-time in Episode Two.

Left 4 Dead 2 introduced flowing water.

It creates water that realistically reflects and refracts the world, and that can flow throughout a map.

Tip:Water does not need to use the Water shader! If a less realistic effect is desired, or the water volume is oddly shaped, other shaders can be used, such as LightmappedGeneric or Refract. The method for creating the materials is the same.

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_cubemap entities throughout a map.
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 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

Flowing water

$scroll1 "[<normal X> <normal Y>]" (in all games since )
$scroll2 "[<normal X> <normal Y>]" (in all games since ): 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.)

Flow maps

$flowmap $flow_normaluvscale $flow_worlduvscale $flow_uvscrolldistance $flow_timeintervalinseconds $flow_timescale $flow_bumpstrength $flow_noise_texture $flow_noise_scale $flow_debug

Basetexture Flow

$basetexture $color_flow_uvscale $color_flow_timescale $color_flow_timeintervalinseconds $color_flow_uvscrolldistance $color_flow_lerpexp $color_flow_displacebynormalstrength

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 flow map, 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 blending from onwards.

There are now tools to assist in painting flowmaps.: Flow field editor from algoholic.eu : http://algoholic.eu/another-flow-field-editor-update/ ^{[dead link]}; 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 ^{[dead link]}

Other

%compilewater $surfaceprop %tooltexture

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.

Water (shader)

Contents

Special behaviour

Shader parameters

Textures

Fog

Reflection