%alphatexture

%alphatexture is an internal material shader parameter available in Garry's Mod and Mapbase.

Used on static props when the prop is flagged for texture shadows and compiling VRAD with -textureshadows. The alpha channel of the specified VTF will be used instead of $basetexture, even if $alphatest and $translucent are absent.

Tip:As this parameter is only used by VRAD, the VTF mentioned does not need to be shipped with the map if it is unused elsewhere.

Code:See this GitHub PR for how to add this to a custom VRAD.
The source code for Mapbase 8.0 includes this implementation.

Syntax

"VertexLitGeneric"
{
    $basetexture "models/props_custom/myprop_base"
    %alphatexture "models/props_custom/myprop_alpha"
}

Potential usecases

%alphatexture is most useful for materials that are translucent enough for light to pass through, but are opaque to the human eye. Common materials that would exhibit this behavior are:

• Foliage such as leaves and grass
• Curtains, awnings, and umbrellas
• Paper

This parameter can be useful in certain other niche instances:

• Making the shadows for a given prop less dark, which can be useful if it uses $halflambert (or $phong without $phongdisablehalflambert).
• When $detailblendmode 4 is used, as the shadows would then make more sense to be cast from $detail
• When $additive is used, as no alpha channel will be present and neither $translucent nor $alphatest are used
• When a shader such as Refract is used, as no alpha channel will be present and neither $translucent nor $alphatest are used, and $basetexture won't be used as the diffuse
• If a shader such as Wireframe is used, as $basetexture will not be present
• When $alpha is used, as VRAD doesn't account for it
• For creating a sharp high-resolution texture shadow without bloating the map's filesize, as the shadow-casting texture does not need to be shipped with the map.

Workaround for other versions of VRAD

If mapping for a game that does not have an SDK that includes the source code to compile your own version of VRAD (ex: ), it is still possible to simulate the effect of %alphatexture by creating a separate $translucent material to use in VRAD only, and setting the alpha texture to that material's $basetexture. To avoid needing to swap VMTs every time the map is being compiled, the -insert_search_path parameter can be used with VRAD, which should take priority over the search paths declared in gameinfo.txt.