URP 渲染实战 / 第 11 章 从零手写 PBR / 案例 11.10
案例 11.10调试视图：把光照拆开看入门
目标：写一个与 MyPBR 共用全部 HLSL 的调试 Shader，单独输出 BRDF 的每一项、光照的每一部分。
Assets/Cookbook/Ch11/MyPBRDebug.shader（节选：debug_frag）
half4 DebugFrag(Varyings i) : SV_Target { MySurface s = MySampleSurface(i.uv); InputData id = MyInitInputData(i, s.normalTS); MyMaterial m = MyInitMaterial(s.albedo, s.metallic, s.perceptualRoughness); int view = (int)_View; // 1~3：只看主光方向上的单项，便于和第 9 章的公式图对照 if (view >= 1 && view <= 3) { Light L = GetMainLight(); float3 N = id.normalWS, V = id.viewDirectionWS, H = SafeNormalize(L.direction + V); float NoV = abs(dot(N, V)) + 1e-5, NoL = saturate(dot(N, L.direction)); float NoH = saturate(dot(N, H)), LoH = saturate(dot(L.direction, H)); if (view == 1) // 归一化的 D：除以峰值 1/(π α²)，范围 0~1 return MyD_GGX(NoH, m.a2) * PI * m.a2 * (NoL > 0); if (view == 2) // G2 = V * 4 NoL NoV，范围 0~1 return MyV_SmithGGXCorrelated(NoV, NoL, m.a2) * 4.0 * NoL * NoV; return half4(MyF_Schlick(m.f0, 1.0, LoH) * (NoL > 0), 1); } MyLightingTerms t = MyComputeLighting(s, m, id); float3 c; switch (view) { case 4: c = t.directSpecular; break; case 5: c = t.directDiffuse; break; case 6: c = t.indirectDiffuse; break; case 7: c = t.indirectSpecular; break; case 8: c = t.directDiffuse + t.directSpecular; break; case 9: c = t.indirectDiffuse + t.indirectSpecular; break; case 10: c = MySamplePrefilteredEnv(reflect(-id.viewDirectionWS, id.normalWS), m.perceptualRoughness, id.positionWS, id.normalizedScreenSpaceUV); break; case 11: { float NoV = saturate(dot(id.normalWS, id.viewDirectionWS)); float2 dfg = MyEnvDFG(NoV, m.perceptualRoughness); c = m.f0 * dfg.x + dfg.y; break; } default: c = t.directDiffuse + t.directSpecular + t.indirectDiffuse + t.indirectSpecular + t.emission; break; } return half4(c, 1); }
vec4 DebugFrag() { MySurface s = MySampleSurface(uv); InputData id = MyInitInputData(s.normalTS); MyMaterial m = MyInitMaterial(s.albedo, s.metallic, s.perceptualRoughness); int view = int(_View); // 1~3：只看主光方向上的单项，便于和第 9 章的公式图对照 if (view >= 1 && view <= 3) { Light L = GetMainLight(); vec3 N = id.normalWS, V = id.viewDirectionWS, H = SafeNormalize(L.direction + V); float NoV = abs(dot(N, V)) + 1e-5, NoL = saturate(dot(N, L.direction)); float NoH = saturate(dot(N, H)), LoH = saturate(dot(L.direction, H)); float lit = NoL > 0.0 ? 1.0 : 0.0; if (view == 1) // 归一化的 D：除以峰值 1/(π α²)，范围 0~1 return vec4(MyD_GGX(NoH, m.a2) * PI * m.a2 * lit); if (view == 2) // G2 = V * 4 NoL NoV，范围 0~1 return vec4(MyV_SmithGGXCorrelated(NoV, NoL, m.a2) * 4.0 * NoL * NoV); return vec4(MyF_Schlick(m.f0, 1.0, LoH) * lit, 1.0); } MyLightingTerms t = MyComputeLighting(s, m, id); vec3 c; switch (view) { case 4: c = t.directSpecular; break; case 5: c = t.directDiffuse; break; case 6: c = t.indirectDiffuse; break; case 7: c = t.indirectSpecular; break; case 8: c = t.directDiffuse + t.directSpecular; break; case 9: c = t.indirectDiffuse + t.indirectSpecular; break; case 10: c = MySamplePrefilteredEnv(reflect(-id.viewDirectionWS, id.normalWS), m.perceptualRoughness, id.positionWS, id.normalizedScreenSpaceUV); break; case 11: { float NoV = saturate(dot(id.normalWS, id.viewDirectionWS)); vec2 dfg = MyEnvDFG(NoV, m.perceptualRoughness); c = m.f0 * dfg.x + dfg.y; break; } default: c = t.directDiffuse + t.directSpecular + t.indirectDiffuse + t.indirectSpecular + t.emission; break; } return vec4(c, 1.0); }
调试视图用一个 _View 浮点属性加运行时分支切换，不产生变体。前三种模式只看主光方向上的单项（图 11-3 就是用它拍的）；之后的模式调用与正式 Shader 完全相同的 MyComputeLighting，只是选择输出哪一部分。这样的调试 Shader 在开发 BRDF 时非常有用：任何一项出错（例如忘了乘 π、NoL 符号反了、环境图 mip 选错），都能在对应视图里一眼看出来。_View 被故意放在 CBUFFER 之外——调试 Shader 不需要 SRP Batcher 兼容，放进去反而要同步修改 MyPBR_Input.hlsl。
第三格值得多看一眼：砖墙地面是电介质，F0 只有 0.04，但远处掠射角的地面反射出了明显的天空颜色——这是菲涅尔效应，DFG 表里 B 项的贡献。很多“手写 PBR”漏掉环境镜面或者只乘 F0 而不乘 DFG，场景远处的地面就会显得“发干”。