PBR Renderer: implemented layerd OIT blend

Author: TheMostDiligent

PBR/src/PBR_Renderer.cpp

@@ -1954,8 +1954,8 @@ void PBR_Renderer::CreatePSO(PsoHashMapType&             PsoHashMap,
 
     RefCntAutoPtr<IShader>& pPS = m_PixelShaders[{
         PSOFlags,
-        // Opaque and Blend modes use the same shader
-        Key.GetAlphaMode() == ALPHA_MODE_MASK ? ALPHA_MODE_MASK : ALPHA_MODE_OPAQUE,
+        // Non-OIT blend uses the same shader as opaque
+        (Key.GetAlphaMode() == ALPHA_MODE_BLEND && OITLayerCount == 0) ? ALPHA_MODE_OPAQUE : Key.GetAlphaMode(),
         CULL_MODE_BACK,
         Key,
     }];
@@ -1987,12 +1987,7 @@ void PBR_Renderer::CreatePSO(PsoHashMapType&             PsoHashMap,
         pPS = m_Device.CreateShader(ShaderCI);
     }
 
-    GraphicsPipeline = GraphicsDesc;
-    if (Key.GetType() == RenderPassType::OITLayers)
-    {
-        GraphicsPipeline.DepthStencilDesc.DepthWriteEnable = False;
-    }
-
+    GraphicsPipeline             = GraphicsDesc;
     GraphicsPipeline.InputLayout = InputLayout;
 
     IPipelineResourceSignature* ppSignatures[MAX_RESOURCE_SIGNATURES];
@@ -2018,7 +2013,8 @@ void PBR_Renderer::CreatePSO(PsoHashMapType&             PsoHashMap,
         VERIFY(Key.GetLoadingAnimation() == LoadingAnimationMode::None, "Loading animation must be disabled for OIT Layers render pass");
         VERIFY(Key.GetDebugView() == DebugViewType::None, "Debug view must be disabled for OIT Layers render pass");
 
-        PSOCreateInfo.GraphicsPipeline.BlendDesc = BS_UpdateOITTail;
+        PSOCreateInfo.GraphicsPipeline.BlendDesc           = BS_UpdateOITTail;
+        GraphicsPipeline.DepthStencilDesc.DepthWriteEnable = False;
     }
     else
     {
@@ -2030,7 +2026,15 @@ void PBR_Renderer::CreatePSO(PsoHashMapType&             PsoHashMap,
         else if (AlphaMode == ALPHA_MODE_BLEND)
         {
             VERIFY(!IsUnshaded, "Unshaded mode should use OpaquePSO. The PSOKey's ctor sets the alpha mode to opaque.");
-            GraphicsPipeline.BlendDesc = BS_PremultipliedAlphaBlend;
+            if (OITLayerCount > 0)
+            {
+                PSOCreateInfo.GraphicsPipeline.BlendDesc           = BS_AdditiveBlend;
+                GraphicsPipeline.DepthStencilDesc.DepthWriteEnable = False;
+            }
+            else
+            {
+                GraphicsPipeline.BlendDesc = BS_PremultipliedAlphaBlend;
+            }
         }
         else
         {

Shaders/PBR/private/RenderPBR.psh

@@ -10,6 +10,10 @@
 #   include "Iridescence.fxh"
 #endif
 
+#if NUM_OIT_LAYERS > 0
+#   include "OIT.fxh"
+#endif
+
 #include "VSOutputStruct.generated"
 // struct VSOutput
 // {
@@ -68,6 +72,11 @@ Texture2DArray<float>  g_ShadowMap;
 SamplerComparisonState g_ShadowMap_sampler;
 #endif
 
+#if NUM_OIT_LAYERS > 0
+StructuredBuffer<uint> g_OITLayers;
+Texture2D<float4>      g_OITTail;
+#endif
+
 PBRMaterialTextureAttribs GetDefaultTextureAttribs()
 {
     PBRMaterialTextureAttribs Attribs;
@@ -371,6 +380,39 @@ float4 GetLoadingAnimationColor(float3 WorldPos, float Factor)
 }
 #endif
 
+#if NUM_OIT_LAYERS > 0
+float GetOITTransmittance(float Depth, uint2 Pos)
+{
+    uint D = uint(Depth * 16777215.0);
+    float T = 1.0;
+    
+    uint Offset = GetOITLayerDataOffset(uint2(Pos.xy), uint2(g_Frame.Camera.f4ViewportSize.xy), uint(NUM_OIT_LAYERS));
+
+    uint layer = 0u;
+    while (layer < uint(NUM_OIT_LAYERS))
+    {
+        uint LayerDT = g_OITLayers[Offset + layer];
+        uint LayerD = GetOITLayerDepth(LayerDT);
+        // +1u helps to avoid precision issues.
+        if (D <= LayerD + 1u)
+        {
+            break;
+        }
+        float LayerT = GetOITLayerTransmittance(LayerDT);
+        T *= LayerT;
+        ++layer;
+    }
+    if (layer == uint(NUM_OIT_LAYERS))
+    {
+        float4 Tail = g_OITTail.Load(int3(Pos.xy, 0));
+        // Average contribution of all tail layers.
+        T /= max(255.0 * Tail.x, 1.0);
+    }
+
+    return T;
+}
+#endif
+
 PSOutput main(in VSOutput VSOut,
               in bool     IsFrontFace : SV_IsFrontFace)
 {
@@ -497,6 +539,13 @@ PSOutput main(in VSOutput VSOut,
     if (BasicAttribs.AlphaMode == PBR_ALPHA_MODE_BLEND)
     {
         OutColor.rgb *= BaseColor.a;
+#if NUM_OIT_LAYERS > 0
+        if (BaseColor.a > OIT_OPACITY_THRESHOLD)
+        {
+            float T = GetOITTransmittance(VSOut.ClipPos.z, uint2(VSOut.ClipPos.xy));
+            OutColor.rgb *= T;
+        }
+#endif
     }
 
     // Add highlight color