feat(cloud shadows): add inner cloud shadowing

features/Cloud Shadows/Shaders/CloudShadows/CloudShadows.hlsli

@@ -1,6 +1,7 @@
 namespace CloudShadows
 {
-	TextureCube<float> CloudShadowsTexture : register(t25);
+	TextureCube<float> VolumetricCloudShadowsTexture : register(t25);
+	TextureCube<float> CloudShadowsTexture : register(t26);
 
 	const static float CloudHeight = (2e3f / 1.428e-2) * 0.25;
 	const static float PlanetRadius = (6371e3f / 1.428e-2);

package/Shaders/Common/SharedData.hlsli

@@ -141,7 +141,8 @@ namespace SharedData
 	struct CloudShadowsSettings
 	{
 		float Opacity;
-		float3 pad0;
+		float InnerCloudShadowOpacity;
+		float2 pad0;
 	};
 
 	struct LODBlendingSettings

package/Shaders/Sky.hlsl

@@ -243,6 +243,36 @@ PS_OUTPUT main(PS_INPUT input)
 	psout.Color.xyz = Color::Sky(input.Color.xyz) * baseColor.xyz + yyy;
 #		endif
 
+#		if defined(CLOUD_SHADOWS) && defined(CLOUDS)
+	if (baseColor.w > 0.0 && SharedData::cloudShadowsSettings.InnerCloudShadowOpacity > 0.0) {
+		float3 viewDir = normalize(input.WorldPosition.xyz);
+		float rayStep = 1.0 / 32.0;
+		float rayPos = rayStep * 0.5;
+		float4 rayShadow = 0.0;
+
+		float3 PoissonDisc[] = {
+			float3(0.460921f, 0.615192f, 0.887539f),
+			float3(0.757347f, 0.911008f, 0.189581f),
+			float3(0.548753f, 0.145482f, 0.0548723f),
+			float3(0.90051f, 0.157048f, 0.623493f)
+		};
+
+		[unroll] for (int i = 0; i < 4; i++)
+		{
+			float3 raySample = normalize(lerp(viewDir, SharedData::DirLightDirection.xyz, rayPos) + (PoissonDisc[i] * 2.0 - 1.0) * 0.01);
+
+			if (raySample.z < 0.0)
+				rayShadow[i] += -raySample.z;
+			else
+				rayShadow[i] = max(rayShadow[i], CloudShadows::VolumetricCloudShadowsTexture.SampleLevel(SampBaseSampler, raySample, 0).x);
+
+			rayPos += rayStep;
+		}
+
+		psout.Color.xyz *= (1.0 - saturate(dot(rayShadow, 0.25)) * SharedData::cloudShadowsSettings.InnerCloudShadowOpacity);
+	}
+#		endif
+
 #	else
 	psout.Color = float4(0, 0, 0, 1.0);
 #	endif  // OCCLUSION

src/Features/CloudShadows.cpp

@@ -2,14 +2,19 @@
 
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(
 	CloudShadows::Settings,
-	Opacity)
+	Opacity,
+	InnerCloudShadowOpacity)
 
 void CloudShadows::DrawSettings()
 {
-	ImGui::SliderFloat("Opacity", &settings.Opacity, 0.0f, 1.0f, "%.1f");
+	ImGui::SliderFloat("Opacity", &settings.Opacity, 0.0f, 1.0f, "%.2f");
 	if (auto _tt = Util::HoverTooltipWrapper()) {
-		ImGui::Text(
-			"Higher values make cloud shadows darker.");
+		ImGui::Text("Controls how dark cloud shadows appear on terrain and objects.");
+	}
+
+	ImGui::SliderFloat("Inner Cloud Shadow Opacity", &settings.InnerCloudShadowOpacity, 0.0f, 1.0f, "%.2f");
+	if (auto _tt = Util::HoverTooltipWrapper()) {
+		ImGui::Text("Controls shadowing applied within the clouds themselves. Higher values make the underside of clouds darker.");
 	}
 }
 
@@ -118,6 +123,8 @@ void CloudShadows::ReflectionsPrepass()
 		ID3D11ShaderResourceView* srv = texCubemapCloudOccCopy->srv.get();
 		context->PSSetShaderResources(25, 1, &srv);
 		context->CSSetShaderResources(25, 1, &srv);
+		context->PSSetShaderResources(26, 1, &srv);
+		context->CSSetShaderResources(26, 1, &srv);
 	}
 }
 
@@ -129,9 +136,15 @@ void CloudShadows::EarlyPrepass()
 
 	auto context = globals::d3d::context;
 
+	// t25 = VolumetricCloudShadowsTexture: use previous-frame copy so there is no D3D11 hazard
+	ID3D11ShaderResourceView* copySrv = texCubemapCloudOccCopy->srv.get();
+	context->PSSetShaderResources(25, 1, &copySrv);
+	context->CSSetShaderResources(25, 1, &copySrv);
+
+	// t26 = CloudShadowsTexture: live cubemap for terrain ground shadows.
 	ID3D11ShaderResourceView* srv = texCubemapCloudOcc->srv.get();
-	context->PSSetShaderResources(25, 1, &srv);
-	context->CSSetShaderResources(25, 1, &srv);
+	context->PSSetShaderResources(26, 1, &srv);
+	context->CSSetShaderResources(26, 1, &srv);
 }
 
 void CloudShadows::SetupResources()
@@ -168,6 +181,12 @@ void CloudShadows::SetupResources()
 			rtvDesc.Format = texDesc.Format;
 			DX::ThrowIfFailed(device->CreateRenderTargetView(texCubemapCloudOccCopy->resource.get(), &rtvDesc, cubemapCloudOccCopyRTVs + i));
 		}
+
+		// Clear copy cubemap so EarlyPrepass doesn't bind uninitialized data on the first frame.
+		auto context = globals::d3d::context;
+		float black[4] = { 0, 0, 0, 0 };
+		for (int i = 0; i < 6; ++i)
+			context->ClearRenderTargetView(cubemapCloudOccCopyRTVs[i], black);
 	}
 	{
 		D3D11_BLEND_DESC blendDesc = {};

src/Features/CloudShadows.h

@@ -9,8 +9,10 @@ struct CloudShadows : Feature
 	struct alignas(16) Settings
 	{
 		float Opacity = 0.8f;
-		float pad[3];
+		float InnerCloudShadowOpacity = 0.5f;
+		float pad[2];
 	};
+	STATIC_ASSERT_ALIGNAS_16(Settings);
 
 	Settings settings;