refactor: consolidate PBR direct lighting calculations

package/Shaders/Common/PBR.hlsli

@@ -384,6 +384,114 @@ namespace PBR
 		}
 	}
 
+	/**
+	 * @brief Calculates and accumulates PBR direct lighting contributions for a single light source
+	 *
+	 * This function handles the core PBR lighting calculation that is identical across all call sites.
+	 * It processes diffuse, specular, transmission, and coat lighting components for a given light
+	 * and accumulates the results into the provided output variables.
+	 *
+	 * @note This function is designed to be called multiple times per pixel (once per light source)
+	 *       and accumulates results rather than returning them. All output parameters are modified in-place.
+	 *
+	 * @param[in] lightColor The RGB color of the light source (should be in linear space)
+	 * @param[in] lightMultiplier Combined multiplier for light intensity (includes shadows, attenuation, etc.)
+	 * @param[in] parallaxShadow Parallax occlusion mapping shadow factor (1.0 = no shadow)
+	 * @param[in] N Surface normal vector in world space
+	 * @param[in] N_coat Coat layer normal vector in world space (used for two-layer materials)
+	 * @param[in] V_refracted View direction after refraction through coat layer
+	 * @param[in] V Original view direction in world space
+	 * @param[in] L_refracted Light direction after refraction through coat layer
+	 * @param[in] L Original light direction in world space
+	 * @param[in] surfaceProperties PBR material properties (roughness, metallic, F0, etc.)
+	 * @param[in] tbnMatrix Transpose of the tangent-bitangent-normal matrix
+	 * @param[in] texCoord Texture coordinates (used for feature texture sampling)
+	 * @param[in,out] diffuseAccumulator Accumulated diffuse lighting contribution (modified in-place)
+	 * @param[in,out] coatDiffuseAccumulator Accumulated coat layer diffuse lighting (modified in-place)
+	 * @param[in,out] transmissionAccumulator Accumulated transmission/translucency contribution (modified in-place)
+	 * @param[in,out] specularAccumulator Accumulated specular lighting contribution (modified in-place, automatically gated by interior status)
+	 *
+	 * @return PBR::LightProperties The calculated light properties, useful for additional effects like wetness
+	 *
+	 * @par Example Usage:
+	 * @code
+	 * // For directional light
+	 * PBR::LightProperties lightProperties = PBR::ProcessPBRDirectLight(
+	 *     dirLightColor,
+	 *     dirLightColorMultiplier * dirDetailShadow,
+	 *     parallaxShadow,
+	 *     N,                    // Surface normal
+	 *     N_coat,               // Coat normal
+	 *     V_refracted,          // Refracted view direction
+	 *     V,                    // View direction
+	 *     L_refracted,          // Refracted light direction
+	 *     L,                    // Light direction
+	 *     pbrSurfaceProperties,
+	 *     tbnMatrix,
+	 *     texCoord,
+	 *     lightsDiffuseColor,
+	 *     coatLightsDiffuseColor,
+	 *     transmissionColor,
+	 *     specularColorPBR);
+	 *
+	 * // Additional effects using the returned light properties
+	 * if (waterRoughnessSpecular < 1.0) {
+	 *     specularColorPBR += PBR::GetWetnessDirectLightSpecularInput(
+	 *         wetnessNormal, V, L,
+	 *         lightProperties.CoatLightColor, waterRoughnessSpecular) * wetnessGlossinessSpecular;
+	 * }
+	 * @endcode
+	 *
+	 * @par Features Supported:
+	 * - Standard PBR lighting (diffuse + specular)
+	 * - Two-layer materials (coat layer)
+	 * - Transmission/translucency effects
+	 * - Interior/exterior lighting adjustments (specular automatically disabled in interiors)
+	 * - Feature texture sampling
+	 *
+	 * @par Performance Notes:
+	 * - Function is marked as @c inline for optimal performance
+	 * - Designed to be called in tight loops for multiple light sources
+	 * - Accumulates results to minimize memory bandwidth
+	 *
+	 * @see PBR::GetDirectLightInput
+	 * @see PBR::InitLightProperties
+	 * @see PBR::SurfaceProperties
+	 */
+	inline LightProperties ProcessPBRDirectLight(
+		float3 lightColor,
+		float lightMultiplier,
+		float parallaxShadow,
+		float3 N,
+		float3 N_coat,
+		float3 V_refracted,
+		float3 V,
+		float3 L_refracted,
+		float3 L,
+		SurfaceProperties surfaceProperties,
+		float3x3 tbnMatrix,
+		float2 texCoord,
+		inout float3 diffuseAccumulator,
+		inout float3 coatDiffuseAccumulator,
+		inout float3 transmissionAccumulator,
+		inout float3 specularAccumulator)
+	{
+		LightProperties lightProperties = InitLightProperties(lightColor, lightMultiplier, parallaxShadow);
+		float3 dirDiffuseColor, coatDirDiffuseColor, dirTransmissionColor, dirSpecularColor;
+
+		GetDirectLightInput(
+			dirDiffuseColor, coatDirDiffuseColor, dirTransmissionColor, dirSpecularColor,
+			N, N_coat, V_refracted, V,
+			L_refracted, L, lightProperties, surfaceProperties, tbnMatrix, texCoord);
+
+		diffuseAccumulator += dirDiffuseColor;
+		coatDiffuseAccumulator += coatDirDiffuseColor;
+		transmissionAccumulator += dirTransmissionColor;
+		specularAccumulator += dirSpecularColor * !SharedData::InInterior;
+
+		return lightProperties;
+	}
+
 	float3 GetWetnessDirectLightSpecularInput(float3 N, float3 V, float3 L, float3 lightColor, float roughness)
 	{
 		const float wetnessStrength = 1;