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feat(extended translucency): "scattering volume" material #1350

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feat(extended translucency): "scattering volume" material #1350

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8 changes: 7 additions & 1 deletion features/Extended Translucency/Shaders/ExtendedTranslucency/ExtendedTranslucency.hlsli
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,8 @@ namespace ExtendedTranslucency
static const uint RimLight = 1;
static const uint IsotropicFabric = 2;
static const uint AnisotropicFabric = 3;
static const uint Disabled = 4; // Any value >= 4
static const uint ScatteringVolume = 4;
static const uint Disabled = 5; // Any value >= 5
}

bool IsValidMaterial(uint Material)
Expand Down Expand Up @@ -41,6 +42,11 @@ namespace ExtendedTranslucency
return a0 * (length(cross(v, t)) + length(cross(v, b))) / (abs(dot(v, n)) + 0.001) - a0 * a0;
}

float GetViewDependentAlphaScatteringVolume(float alpha, float3 view, float3 normal)
{
return 1.0 - pow(1.0 - alpha, dot(view, normal));
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@ArcEarth ArcEarth Aug 8, 2025

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The distance a ray of light traveled in a sphere is 2R*cos(theta), which scatters light at exp(k*2R*cos(theta)) where k is a absorbing factor. k can be deduced from the input alpha, assuming its the transparency when viewing from its normal direction.
And the math turns out to be this simple...

}

float SoftClamp(float alpha, float limit)
{
// soft clamp [alpha,1] and remap the transparency
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6 changes: 5 additions & 1 deletion package/Shaders/Lighting.hlsl
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Expand Up @@ -3205,7 +3205,7 @@ PS_OUTPUT main(PS_INPUT input, bool frontFace : SV_IsFrontFace)

[branch] if (ExtendedTranslucency::IsValidMaterial(AlphaMaterialModel))
{
if (alpha >= 0.0156862754 && alpha < 1.0) {
if (alpha >= 0.0156862754 && alpha <= 1.0 - 0.0156862754) {
float originalAlpha = alpha;
alpha = alpha * (1.0 - AlphaMaterialReduction);
[branch] if (AlphaMaterialModel == ExtendedTranslucency::MaterialModel::AnisotropicFabric)
Expand All @@ -3220,6 +3220,10 @@ PS_OUTPUT main(PS_INPUT input, bool frontFace : SV_IsFrontFace)
{
alpha = ExtendedTranslucency::GetViewDependentAlphaFabric1D(alpha, viewDirection, worldNormal.xyz);
}
else if (AlphaMaterialModel == ExtendedTranslucency::MaterialModel::ScatteringVolume)
{
alpha = ExtendedTranslucency::GetViewDependentAlphaScatteringVolume(alpha, viewDirection, worldNormal.xyz);
}
else
{
alpha = ExtendedTranslucency::GetViewDependentAlphaNaive(alpha, viewDirection, worldNormal.xyz);
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6 changes: 4 additions & 2 deletions src/Features/ExtendedTranslucency.cpp
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Expand Up @@ -90,6 +90,7 @@ void ExtendedTranslucency::DrawSettings()
"1 - Rim Edge",
"2 - Isotropic Fabric, Glass, ...",
"3 - Anisotropic Fabric",
"4 - Scattering Volume",
};

static constexpr int AlphaModeSize = static_cast<int>(std::size(AlphaModeNames));
Expand All @@ -104,7 +105,8 @@ void ExtendedTranslucency::DrawSettings()
" - Disabled: No anisotropic transluency, flat alpha.\n"
" - Rim Edge: Naive rim light effect with no physics model, the edge of the geometry is always opaque even its full transparent.\n"
" - Isotropic Fabric: Imaginary fabric weaved from threads in one direction, respect normal map, also works well for layer of glass panels.\n"
" - Anisotropic Fabric: Common fabric weaved from tangent and birnormal direction, ignores normal map.\n");
" - Anisotropic Fabric: Common fabric weaved from tangent and birnormal direction, ignores normal map.\n"
" - Scattering Volume: A **volumn** (instead of a layer) of light scattering or absoring material, it fade the geometry out at its edge instead of strength them like other material.\n");
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@Pentalimbed Pentalimbed Aug 12, 2025 •
edited
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Spelling and grammar mistakes:

  • volumn - volume
  • absoring - absorbing
  • what does "fade the geometry out at its edge instead of strength(en?) them" mean? It becomes more transparent towards the edges instead of the other way around?

I suggest you put your texts through a spell checker or LLM

}
if (ImGui::Checkbox("Skinned Mesh Only", &settings.SkinnedOnly)) {
changed = true;
Expand Down Expand Up @@ -160,7 +162,7 @@ std::pair<std::string, std::vector<std::string>> ExtendedTranslucency::GetFeatur
return {
"Extended Translucency provides realistic rendering of thin fabric and other translucent materials.\n"
"This feature supports multiple material models for different types of translucent surfaces.",
{ "Multiple translucency material models (rim edge, isotropic/anisotropic fabric)",
{ "Multiple translucency material models (rim edge, isotropic/anisotropic fabric, scattering volume)",
"Realistic fabric translucency with directional light transmission",
"Per-material override support via NIF extra data",
"Configurable transparency and softness controls",
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1 change: 1 addition & 0 deletions src/Features/ExtendedTranslucency.h
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Expand Up @@ -32,6 +32,7 @@ struct ExtendedTranslucency final : Feature
RimLight = 1, // Similar effect like rim light
IsotropicFabric = 2, // 1D fabric model, respect normal map
AnisotropicFabric = 3, // 2D fabric model alone tangent and binormal, ignores normal map
ScatteringVolume = 4, // Fade out at the edge, models a ball of fog (light decays in exponential on distance)

DescriptorUseDefault = 0, // In ExtraFeatureDescriptor, 0 means 'UseDefault' instead of 'Disabled'
DescriptorDisabled = 7, // In ExtraFeatureDescriptor, value >= 5 means 'Disabled'
Expand Down
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