Lightmapped_4WayBlend

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Lightmapped_4WayBlend is a material shader available in the following Source engine games: <Counter-Strike: Global Offensive> Counter-Strike: Global Offensive, <Black Mesa (Source)> Black Mesa. It is a shader that blends the vertices of a displacement surface between four different materials. It handles four at once by using mirrored sets of parameters with "2", "3", or "4" in their name.

The first 2 textures can have bumpmaps like WorldVertexTransition. If you want to use an envmap and have masking then you should use the alpha channels of the base textures and $basealphaenvmapmask. This shader does not support $normalmapalphaenvmapmask in <Counter-Strike: Global Offensive>. You can use an $envmapmask texture, but you'll have to hand paint it to match what you want on the blended result.

Being a replacement of the older Multiblend shader, it was introduced to <Counter-Strike: Global Offensive> for the map cs_insertion.

Note:This shader only works on displacements.
Note:This shader is only available in <Counter-Strike: Global Offensive> and <Black Mesa (Source)> as of June 2019.

Warning: This shader does not support $normalmapalphaenvmapmask in <Counter-Strike: Global Offensive>. It does in <Black Mesa (Source)>.

To do: Document if <Black Mesa (Source)>'s version of the shader has any more differences from <Counter-Strike: Global Offensive>'s.
Bug: This shader won't draw the painted blends you put in if Hammer's 3D View is set to "3D Shaded Textured Polygons", remember to set the 3D View back to "3D Textured" when painting your blends.

Example

Lightmapped_4WayBlend
{
    "$basetexture"              "brick_a"
    "$bumpmap"                  "brick_a_normal"
    "$texture1_lumstart"        "0.0"
    "$texture1_lumend"          "0.5"
"$basetexture2" "brick_a" "$ssbump" "1" "$bumpmap2" "brick_a_normal" "$surfaceprop" "concrete" "$texture2_lumstart" "0.0" "$texture2_lumend" "0.5" "$texture2_blendmode" "0" "$texture2_blendstart" "0.8" "$texture2_blendend" "0.9" "$texture2_uvscale" "[1.0 1.0]" "$texture2_bumpblendfactor" "0.7"
"$basetexture3" "brick_a_bottom_grime" "$texture3_blendmode" "0" "$texture3_uvscale" "[2.0 2.0]" "$texture3_lumstart" "0.0" "$texture3_lumend" "0.05" "$texture3_blendstart" "0.8" "$texture3_blendend" "1.0" "$texture3_bumpblendfactor" "0.7"
"$basetexture4" "brick_a_top_grime" "$texture4_blendmode" "0" "$texture4_uvscale" "[2.0 2.0]" "$texture4_lumstart" "0.0" "$texture4_lumend" "0.2" "$texture4_blendstart" "0.90" "$texture4_blendend" "0.99" "$texture4_bumpblendfactor" "0.3"
"$detail" "detail\noise_detail_01" "$detailscale" "[ 32 32 ]" "$detailblendfactor" "0.7" "$detailblendfactor2" "0.4" "$detailblendfactor3" "0.2" "$detailblendfactor4" "0.2"
"$lumblendfactor2" "0.5" "$lumblendfactor3" "0.7" "$lumblendfactor4" "0.4" }

Controlling Blending

The blend tools inside the displacement sculpt window.

The pattern of the blend is defined by Hammer's sculpt window blend tool (shown in the picture on the right). The texture preview in Hammer requires you to set up additional VMT files for each texture to show up in the dialog. Those are not used by the shader itself. The Alpha Blend and Color Blend features of this dialog are disabled when using 4WayBlend, they are only used by the Multiblend material.

The blend can be tuned between being a linear gradient and a more realistic look using the luminance of each basetexture adjusted by parameters. This is done using some simple math in the shader, and avoids requiring extra textures.

Source texture 1
Source texture 2
Source texture 3
Source texture 4
In game example of 4WayBlend.

Luminance Adjust

The lumstart and lumend parameters adjust the luminance value into a usable range with a smoothstep.

luminance = smoothstep( lumstart, lumend, luminanceof(basetexture) )

You can think of this as adjusting the contrast of the luminance. In general, you need more contrast to get a more interesting blend.

Luminance without any adjusting
lumstart = 0.0, lumend = 0.5
lumstart = 0.0, lumend = 0.2
Note:You can invert the result by swapping the lumstart and lumend values. For example, if your texture is of dark tiles with a bright grout, then you probably want to use the inverse luminance so that the tiles drop out after the grout.

Luminance Blending

When blending a given layer, you can choose between using the luminance of that layer or the inverse of blended luminance of the layers below it. This is done with the lumblendfactor parameters.

lumblendfactor = 1.0
lumblendfactor = 0.5
lumblendfactor = 0.0

Vertex Blend Modulate

The resulting luminance is used to modulate the vertex blend value with this formula:

blend = vertexblend * luminance + vertexblend. 

The vertexblend is what you paint using the blend tool in hammer.

Blend without Luminance
Blend with Luminance

Blend Adjust

Finally, the result of that formula is adjusted by another smoothstep with the blendstart and blendend parameters.

blend = smoothstep( blendstart, blendend, blend )

You can think of this as adjusting the sharpness of the blend.

blendstart = 0.75, blendend = 1.0
blendstart = 0.90, blendend = 1.0

Parameters

Most of these parameters have counterparts that can be applied to the first, second, third or fourth layers of a material. For brevity's sake, this will be indicated by 1 to 4 where applicable. Note that a lack of 1 means that, if intended for use with the first layer, there should simply be no number in that place.

$basetexture to $basetexture4 <texture>
See $basetexture. Defines the albedo texture for a given layer.
$surfaceprop to $surfaceprop4 <property>
See $surfaceprop. Defines the type of surface and its properties for a given layer.
$surfacepropalpha <property>
To do: What is this?
$surfacepropalphafilter <float>
To do: What is this?
$bumpmap to $bumpmap4 <texture>
See $bumpmap. Defines the bumpmap for a given layer.
$ssbump <boolean>
See $ssbump. Defines whether or not the bumpmap is self-shadowing.
$basenormalmap2 to $basenormalmap4 <texture> (Only in Black Mesa)
To do: What is the difference between these and $bumpmap2 to $bumpmap4?
$seamless_scale <float>
See $seamless_scale. Mitigates displacement texture stretching across the whole material.
$texture1_lumstart to $texture4_lumstart <normal>
Used with $texture1_lumend to $texture4_lumend to adjust the luminance range used to modulate blending.
$texture1_lumend to $texture4_lumend <normal>
Note:A smoothstep operation is performed on the luminance of the texture, like so: smoothstep(lumstart, lumend, luminanceof(texture)).
$texture1_uvscale to texture4_uvscale <vector2>
Sets the scale of the UV.
Note:Base texture is assumed to be 512x512px, larger textures will be scaled to fit 512x512.
Note:Changing UV scale of the base texture will scale all other textures as well, and can be compensated for by scaling other textures in the opposite direction.
$texture2_blendstart to $texture4_blendstart <normal>
Used with $texture2_blendend to $texture4_blendend to define the blend range in a given layer.
$texture2_blendend to texture4_blendend <normal>
Note:A smoothstep operation is performed on the blend, like so: smoothstep(blendstart, blendend, blend).
$texture2_blendmode to $texture4_blendmode <integer>
Defines the blend mode for a given layer. You can choose between normal blending by setting it to 0, the default, or modulate 2x blending by setting it to 1.
$texture2_bumpblendfactor to $texture4_bumpblendfactor <normal>
Defines how much the $bumpmap is shown for a given layer.
Note:If the material has a $bumpmap to $bumpmap4 defined, then this parameter is ignored. Instead the bumpmaps blend the same as they would in WorldVertexTransition.
$detail <texture>
See $detail. Defines a detail texture for the whole material.
Confirm:Does $detail[2/3/4] exist/can it be used?
$detailblendfactor2 to $detailblendfactor4 <normal>
See $detailblendfactor. Acts as a sort of opacity for the $detail texture specified.
$lumblendfactor2 to $lumblendfactor4 <normal>
Defines luminance value to use for blending for a given layer.
Confirm:Does $lumblendfactor1 exist?
Note:This is choosing between the luminance of the given layer and the inverse of the blended luminance of the layers below it using a lerp: lerp( 1 - blended_lum_of_layers_below, lum_of_current_layer, lumblendfactor )

See also