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Fix sampling textures in decals to use custom mip-level

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#3599
This commit is contained in:
Wojtek Figat
2025-08-14 22:14:03 +02:00
parent cb92a2b8cb
commit bf9ca14deb
3 changed files with 72 additions and 12 deletions
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61
Content/Editor/MaterialTemplates/Decal.shader
View File

@@ -13,7 +13,7 @@
META_CB_BEGIN(0, Data)
float4x4 WorldMatrix;
float4x4 InvWorld;
float4x4 SVPositionToWorld;
float4x4 SvPositionToWorld;
@1META_CB_END
// Use depth buffer for per-pixel decal layering
@@ -27,12 +27,63 @@ struct MaterialInput
float3 WorldPosition;
float TwoSidedSign;
float2 TexCoord;
float4 TexCoord_DDX_DDY;
float3x3 TBN;
float4 SvPosition;
float3 PreSkinnedPosition;
float3 PreSkinnedNormal;
};
// Calculates decal texcoords for a given pixel position (sampels depth buffer and projects value to decal space).
float2 SvPositionToDecalUV(float4 svPosition)
{
float2 screenUV = svPosition.xy * ScreenSize.zw;
svPosition.z = SAMPLE_RT(DepthBuffer, screenUV).r;
float4 positionHS = mul(float4(svPosition.xyz, 1), SvPositionToWorld);
float3 positionWS = positionHS.xyz / positionHS.w;
float3 positionOS = mul(float4(positionWS, 1), InvWorld).xyz;
return positionOS.xz + 0.5f;
}
// Manually compute ddx/ddy for decal texture cooordinates to avoid the 2x2 pixels artifacts on the edges of geometry under decal
// [Reference: https://www.humus.name/index.php?page=3D&ID=84]
float4 CalculateTextureDerivatives(float4 svPosition, float2 texCoord)
{
float4 svDiffX = float4(1, 0, 0, 0);
float2 uvDiffX0 = texCoord - SvPositionToDecalUV(svPosition - svDiffX);
float2 uvDiffX1 = SvPositionToDecalUV(svPosition + svDiffX) - texCoord;
float2 dx = dot(uvDiffX0, uvDiffX0) < dot(uvDiffX1, uvDiffX1) ? uvDiffX0 : uvDiffX1;
float4 svDiffY = float4(0, 1, 0, 0);
float2 uvDiffY0 = texCoord - SvPositionToDecalUV(svPosition - svDiffY);
float2 uvDiffY1 = SvPositionToDecalUV(svPosition + svDiffY) - texCoord;
float2 dy = dot(uvDiffY0, uvDiffY0) < dot(uvDiffY1, uvDiffY1) ? uvDiffY0 : uvDiffY1;
return float4(dx, dy);
}
// Computes the mipmap level for a specific texture dimensions to be sampled at decal texture cooordinates.
// [Reference: https://hugi.scene.org/online/coding/hugi%2014%20-%20comipmap.htm]
float CalculateTextureMipmap(MaterialInput input, float2 textureSize)
{
float2 dx = input.TexCoord_DDX_DDY.xy * textureSize;
float2 dy = input.TexCoord_DDX_DDY.zw * textureSize;
float d = max(dot(dx, dx), dot(dy, dy));
return (0.5 * 0.5) * log2(d); // Hardcoded half-mip rate reduction to avoid artifacts when decal is moved over dither texture
}
float CalculateTextureMipmap(MaterialInput input, Texture2D t)
{
float2 textureSize;
t.GetDimensions(textureSize.x, textureSize.y);
return CalculateTextureMipmap(input, textureSize);
}
float CalculateTextureMipmap(MaterialInput input, TextureCube t)
{
float2 textureSize;
t.GetDimensions(textureSize.x, textureSize.y);
return CalculateTextureMipmap(input, textureSize);
}
// Transforms a vector from tangent space to world space
float3 TransformTangentVectorToWorld(MaterialInput input, float3 tangentVector)
{
@@ -116,7 +167,6 @@ Material GetMaterialPS(MaterialInput input)
}
// Input macro specified by the material: DECAL_BLEND_MODE
#define DECAL_BLEND_MODE_TRANSLUCENT 0
#define DECAL_BLEND_MODE_STAIN 1
#define DECAL_BLEND_MODE_NORMAL 2
@@ -153,7 +203,7 @@ void PS_Decal(
float2 screenUV = SvPosition.xy * ScreenSize.zw;
SvPosition.z = SAMPLE_RT(DepthBuffer, screenUV).r;
float4 positionHS = mul(float4(SvPosition.xyz, 1), SVPositionToWorld);
float4 positionHS = mul(float4(SvPosition.xyz, 1), SvPositionToWorld);
float3 positionWS = positionHS.xyz / positionHS.w;
float3 positionOS = mul(float4(positionWS, 1), InvWorld).xyz;
@@ -166,8 +216,9 @@ void PS_Decal(
materialInput.TexCoord = decalUVs;
materialInput.TwoSidedSign = 1;
materialInput.SvPosition = SvPosition;
// Build tangent to world transformation matrix
materialInput.TexCoord_DDX_DDY = CalculateTextureDerivatives(materialInput.SvPosition, materialInput.TexCoord);
// Calculate tangent-space
float3 ddxWp = ddx(positionWS);
float3 ddyWp = ddy(positionWS);
materialInput.TBN[0] = normalize(ddyWp);

4
Source/Engine/Graphics/Materials/DecalMaterialShader.cpp
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@@ -16,7 +16,7 @@
PACK_STRUCT(struct DecalMaterialShaderData {
Matrix WorldMatrix;
Matrix InvWorld;
Matrix SVPositionToWorld;
Matrix SvPositionToWorld;
});
DrawPass DecalMaterialShader::GetDrawModes() const
@@ -67,7 +67,7 @@ void DecalMaterialShader::Bind(BindParameters& params)
0, 0, 1, 0,
-1.0f, 1.0f, 0, 1);
const Matrix svPositionToWorld = offsetMatrix * view.IVP;
Matrix::Transpose(svPositionToWorld, materialData->SVPositionToWorld);
Matrix::Transpose(svPositionToWorld, materialData->SvPositionToWorld);
}
// Bind constants

19
Source/Engine/Tools/MaterialGenerator/MaterialGenerator.Textures.cpp
View File

@@ -34,7 +34,6 @@ MaterialValue* MaterialGenerator::sampleTextureRaw(Node* caller, Value& value, B
const bool isArray = texture->Type == MaterialParameterType::GPUTextureArray;
const bool isVolume = texture->Type == MaterialParameterType::GPUTextureVolume;
const bool isNormalMap = texture->Type == MaterialParameterType::NormalMap;
const bool canUseSample = CanUseSample(_treeType);
MaterialGraphBox* valueBox = parent->GetBox(1);
// Check if has variable assigned
@@ -63,6 +62,16 @@ MaterialValue* MaterialGenerator::sampleTextureRaw(Node* caller, Value& value, B
// Check if hasn't been sampled during that tree eating
if (valueBox->Cache.IsInvalid())
{
bool canUseSample = CanUseSample(_treeType);
String mipLevel = TEXT("0");
const auto layer = GetRootLayer();
if (layer && layer->Domain == MaterialDomain::Decal && _treeType == MaterialTreeType::PixelShader)
{
// Decals use computed mip level due to ddx/ddy being unreliable
canUseSample = false;
mipLevel = String::Format(TEXT("CalculateTextureMipmap(input, {})"), texture->ShaderName);
}
// Check if use custom UVs
String uv;
MaterialGraphBox* uvBox = parent->GetBox(0);
@@ -94,10 +103,10 @@ MaterialValue* MaterialGenerator::sampleTextureRaw(Node* caller, Value& value, B
// Sample texture
if (isNormalMap)
{
const Char* format = canUseSample ? TEXT("{0}.Sample({1}, {2}).xyz") : TEXT("{0}.SampleLevel({1}, {2}, 0).xyz");
const Char* format = canUseSample ? TEXT("{0}.Sample({1}, {2}).xyz") : TEXT("{0}.SampleLevel({1}, {2}, {3}).xyz");
// Sample encoded normal map
const String sampledValue = String::Format(format, texture->ShaderName, sampler, uv);
const String sampledValue = String::Format(format, texture->ShaderName, sampler, uv, mipLevel);
const auto normalVector = writeLocal(VariantType::Float3, sampledValue, parent);
// Decode normal vector
@@ -123,12 +132,12 @@ MaterialValue* MaterialGenerator::sampleTextureRaw(Node* caller, Value& value, B
}
else*/
{
format = canUseSample ? TEXT("{0}.Sample({1}, {2})") : TEXT("{0}.SampleLevel({1}, {2}, 0)");
format = canUseSample ? TEXT("{0}.Sample({1}, {2})") : TEXT("{0}.SampleLevel({1}, {2}, {3})");
}
}
// Sample texture
String sampledValue = String::Format(format, texture->ShaderName, sampler, uv, _ddx.Value, _ddy.Value);
String sampledValue = String::Format(format, texture->ShaderName, sampler, uv, mipLevel);
valueBox->Cache = writeLocal(VariantType::Float4, sampledValue, parent);
}
}