Tooltexture

Used to blend texture previews in Hammer.

In Hammer and in-game, the material is scaled down to the size of the tooltexture. Unfortunately, you can't make the preview smaller to save space. You'll need one as large as the material you want to display.

The texture to the left

WorldVertexTransition
{
$basetexture    dirt/blend1_mountain_dirt_a1
$basetexture2   dirt/blend2_mountain_dirt_a1
%tooltexture    preview/blend_mountain_dirt_a1
$bumpmap        dirt/blend_mountain_dirt_a1-ssbump
$ssbump         1
%detailtype     desert1
$detail         dirt/blend_mountain_dirt_a1_DM
$surfaceprop    dirt
$surfaceprop2   rock
}

Without a tooltexture, Hammer will only show your first $basetexture, making it impossible to see the blend without compiling.