$blendmodulatetexture

Without vs With. The technique was first used in Day of Defeat's snow maps, such as Kalt.

The green channel of DOD's ground\snowblendtexture.

A custom blend modulation mask (all channels) side-by-side its affected texture rendered in-game.

Template:Shaderparam It changes the transition between the textures from a smooth, linear gradient to one "stamped" with a pattern.

You should use $blendmodulatetexture wherever possible, as the improvement in visual quality is immense!

Caveats

• Incompatible with $normalmapalphaenvmapmask (use $envmapmask instead).
• In Source 2006/2007 and Team Fortress 2, incompatible with $basetexturetransform and $detail.
• In Source 2006, incompatible with $envmaptint and $envmapmask.
• In Alien Swarm, modulation textures are not aligned correctly. Use $blendmasktransform "center .5 .5 scale 1 -1 rotate 90 translate 0 0" to fix them up.

In some cases, textures will blend as if $blendmodulatetexture were not used:

• Does not display when viewed through water.
  Todo: Only in earlier games?
• Does not display when illuminated with player's flashlight in Half-Life 2. This is fixed in Mapbase.
• Does not display in the Hammer Editor in most games. Counter-Strike: Global Offensive and Mapbase are known exceptions.
  Todo: Does it show up in the editors of any other games?

Parameters

$blendmodulatetexture $blendmasktransform

Blend Modulation Textures

Tip:The best way to create a modulation texture is to import the two albedos to an image editor as layers, and create an alpha channel there by hand.

Only two colour channels are read from the texture:

Green

Biases in favor of $basetexture; high-value areas will be the most resistant to modulation. 128 is normal.

The idea is to paint noise and patterns into this channel, so that the edge between the two textures becomes irregular. Valve's snow texture (see right) has lots of ragged edges in the green channel, and even some bootprints. There are also lines painted along the edges of the albedo's bricks that give them a tendency to have snow along their edges.

Red

Sharpens. 0 makes the transition binary, 255 effectively disables modulation.

The red channel of Valve's snow modulation texture is a constant 99, which produces a fairly sharp falloff. Using different values in different places has the potential to produce a more complex effect.

There is not always a need for the texture to be high resolution - high frequency blends can be produced from low-res textures.