88 lines
4.1 KiB
HLSL
88 lines
4.1 KiB
HLSL
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// Main Physically Based BRDF
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//
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half4 BRDF1_ATG_PBS (half3 diffColor, half3 specColor, half oneMinusReflectivity, half smoothness,
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half3 normal, half3 viewDir,
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UnityLight light, UnityIndirect gi,
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// added:
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half specularIntensity)
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{
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half perceptualRoughness = SmoothnessToPerceptualRoughness (smoothness);
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half3 halfDir = Unity_SafeNormalize (light.dir + viewDir);
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// NdotV should not be negative for visible pixels, but it can happen due to perspective projection and normal mapping
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// In this case normal should be modified to become valid (i.e facing camera) and not cause weird artifacts.
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// but this operation adds few ALU and users may not want it. Alternative is to simply take the abs of NdotV (less correct but works too).
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// Following define allow to control this. Set it to 0 if ALU is critical on your platform.
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// This correction is interesting for GGX with SmithJoint visibility function because artifacts are more visible in this case due to highlight edge of rough surface
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// Edit: Disable this code by default for now as it is not compatible with two sided lighting used in SpeedTree.
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// This will be defined by the Unity BRDF
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// #define UNITY_HANDLE_CORRECTLY_NEGATIVE_NDOTV 0
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#if UNITY_HANDLE_CORRECTLY_NEGATIVE_NDOTV
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// The amount we shift the normal toward the view vector is defined by the dot product.
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half shiftAmount = dot(normal, viewDir);
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normal = shiftAmount < 0.0f ? normal + viewDir * (-shiftAmount + 1e-5f) : normal;
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// A re-normalization should be applied here but as the shift is small we don't do it to save ALU.
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//normal = normalize(normal);
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half nv = saturate(dot(normal, viewDir)); // TODO: this saturate should no be necessary here
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#else
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half nv = abs(dot(normal, viewDir)); // This abs allow to limit artifact
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#endif
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half nl = saturate(dot(normal, light.dir));
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half nh = saturate(dot(normal, halfDir));
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half lv = saturate(dot(light.dir, viewDir));
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half lh = saturate(dot(light.dir, halfDir));
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// Diffuse term
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half diffuseTerm = DisneyDiffuse(nv, nl, lh, perceptualRoughness) * nl;
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// Specular term
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// HACK: theoretically we should divide diffuseTerm by Pi and not multiply specularTerm!
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// BUT 1) that will make shader look significantly darker than Legacy ones
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// and 2) on engine side "Non-important" lights have to be divided by Pi too in cases when they are injected into ambient SH
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half roughness = PerceptualRoughnessToRoughness(perceptualRoughness);
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#if UNITY_BRDF_GGX
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half V = SmithJointGGXVisibilityTerm (nl, nv, roughness);
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half D = GGXTerm (nh, roughness);
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#else
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// Legacy
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half V = SmithBeckmannVisibilityTerm (nl, nv, roughness);
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half D = NDFBlinnPhongNormalizedTerm (nh, PerceptualRoughnessToSpecPower(perceptualRoughness));
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#endif
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half specularTerm = V*D * UNITY_PI; // Torrance-Sparrow model, Fresnel is applied later
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# ifdef UNITY_COLORSPACE_GAMMA
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specularTerm = sqrt(max(1e-4h, specularTerm));
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# endif
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// specularTerm * nl can be NaN on Metal in some cases, use max() to make sure it's a sane value
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specularTerm = max(0, specularTerm * nl);
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// surfaceReduction = Int D(NdotH) * NdotH * Id(NdotL>0) dH = 1/(roughness^2+1)
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half surfaceReduction;
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# ifdef UNITY_COLORSPACE_GAMMA
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surfaceReduction = 1.0-0.28*roughness*perceptualRoughness; // 1-0.28*x^3 as approximation for (1/(x^4+1))^(1/2.2) on the domain [0;1]
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# else
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surfaceReduction = 1.0 / (roughness*roughness + 1.0); // fade \in [0.5;1]
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# endif
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// To provide true Lambert lighting, we need to be able to kill specular completely.
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specularTerm *= any(specColor) ? 1.0 : 0.0;
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// Grass
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half3 specular = specularTerm * FresnelTerm(specColor, lh) * specularIntensity;
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half grazingTerm = saturate(smoothness + (1-oneMinusReflectivity));
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half3 color = diffColor * (gi.diffuse + light.color * diffuseTerm)
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+ specular * light.color //* FresnelTerm (specColor, lh)
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+ surfaceReduction * gi.specular * FresnelLerp (specColor, grazingTerm, nv);
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return half4(color, specular.r /*1*/);
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}
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