【UE4】指数密度高度雾

https://zhuanlan.zhihu.com/p/76627240
指数密度高度雾总共分为4个板块，完成了其中的两个板块

https://blog.csdn.net/netyeaxi/article/details/87437880

控制台设置

SceneRendering.cpp
FSceneRenderer::PostVisibilityFrameSetup
InitFogConstants();

Common.ush

// also see ConvertToDeviceZ()
// @param DeviceZ value that is stored in the depth buffer (Z/W)
// @return SceneDepth (linear in world units, W)
float ConvertFromDeviceZ(float DeviceZ)
{// Supports ortho and perspective, see CreateInvDeviceZToWorldZTransform()return DeviceZ * View.InvDeviceZToWorldZTransform[0] + View.InvDeviceZToWorldZTransform[1] + 1.0f / (DeviceZ * View.InvDeviceZToWorldZTransform[2] - View.InvDeviceZToWorldZTransform[3]);
}

shader中关于View相关的代码在：SceneView.cpp
L2424

ViewUniformShaderParameters.ScreenToTranslatedWorld = FMatrix(FPlane(1, 0, 0, 0),FPlane(0, 1, 0, 0),FPlane(0, 0, ProjectionMatrixUnadjustedForRHI.M[2][2], 1),FPlane(0, 0, ProjectionMatrixUnadjustedForRHI.M[3][2], 0))* InViewMatrices.GetInvTranslatedViewProjectionMatrix();

L2251

 // to bring NDC (-1..1, 1..-1) into 0..1 UV for BufferSize texturesconst FVector4 ScreenPositionScaleBias(EffectiveViewRect.Width() * InvBufferSizeX / +2.0f,EffectiveViewRect.Height() * InvBufferSizeY / (-2.0f * GProjectionSignY),(EffectiveViewRect.Height() / 2.0f + EffectiveViewRect.Min.Y) * InvBufferSizeY,(EffectiveViewRect.Width() / 2.0f + EffectiveViewRect.Min.X) * InvBufferSizeX);

RenderUtils.cpp
QuadVertex

 virtual void InitRHI() override{// create a static vertex bufferFRHIResourceCreateInfo CreateInfo;VertexBufferRHI = RHICreateVertexBuffer(sizeof(FVector2D) * 4, BUF_Static, CreateInfo);void* VoidPtr = RHILockVertexBuffer(VertexBufferRHI, 0, sizeof(FVector2D) * 4, RLM_WriteOnly);static const FVector2D Vertices[4] ={FVector2D(-1,-1),FVector2D(-1,+1),FVector2D(+1,-1),FVector2D(+1,+1),};FMemory::Memcpy(VoidPtr, Vertices, sizeof(FVector2D) * 4);RHIUnlockVertexBuffer(VertexBufferRHI);}

// FogStruct.ExponentialFogParameters: FogDensity * exp2(-FogHeightFalloff * (CameraWorldPosition.z - FogHeight)) in x, FogHeightFalloff in y, MaxWorldObserverHeight in z, StartDistance in w.
// FogStruct.ExponentialFogParameters2: FogDensitySecond * exp2(-FogHeightFalloffSecond * (CameraWorldPosition.z - FogHeightSecond)) in x, FogHeightFalloffSecond in y, FogDensitySecond in z, FogHeightSecond in w
// FogStruct.ExponentialFogParameters3: FogDensity in x, FogHeight in y, whether to use cubemap fog color in z, FogCutoffDistance in w.

//ExponentialFogParameters

y和雾高度衰减有关
z=65536+HeiFog的z
w=

y=雾高度
w=

w=1-雾最大不透明度

引擎版

复制版

shader

参数设置

// FogStruct.ExponentialFogParameters: FogDensity * exp2(-FogHeightFalloff * (CameraWorldPosition.z - FogHeight)) in x, FogHeightFalloff in y, MaxWorldObserverHeight in z, StartDistance in w.
// FogStruct.ExponentialFogParameters2: FogDensitySecond * exp2(-FogHeightFalloffSecond * (CameraWorldPosition.z - FogHeightSecond)) in x, FogHeightFalloffSecond in y, FogDensitySecond in z, FogHeightSecond in w
// FogStruct.ExponentialFogParameters3: FogDensity in x, FogHeight in y, whether to use cubemap fog color in z, FogCutoffDistance in w.
static const float3 MyFogColor = float3(0.528, 0.646, 1.0);
static const float FogHeightFalloff = 0.001;
//Why not 0 or 1 or 2 .when set FogHeightFalloff value to 2 in editor it set 0.002 actually??Why
//it becomes constance when value=0
static const float GlobalDensity = 0.0003;
//this value is used to control the global fog density//using a special starting distance to limit the inscattering to the distance
static const float DirectionalInscatteringStartDistance=10312;
static const float3 DirectionalInscatteringColor = float3(0.0, 2.594,0.615);
static const float3 InscatterinLightDirection = float3(0.506, 0.863, 0.00);
static const float DirectionalInscatteringStrenthFactor = 8.0;

雾密度计算+积分计算

float CalculateLineIntegralShared(float RayDirectionZ)
{//积分拟合函数//RayDirectionZ 人眼与物体的相对高度//雾效影响程度受到 物体高度的影响。越高的物体，到达人眼雾效消失的越严重，越低的物体，到达人眼以后，雾效会加强。float Falloff = max(-127.0f, FogHeightFalloff * RayDirectionZ); // if it's lower than -127.0, then exp2() goes crazy in OpenGL's GLSL.float LineIntegral = (1.0f - exp2(-Falloff)) / Falloff;float LineIntegralTaylor = log(2.0) - (0.5 * Pow2(log(2.0))) * Falloff; // Taylor expansion around 0//float FogDensity = GlobalDensity * exp2(-FogHeightFalloff * (CameraWorldPosition.z - FogHeight));//we set fogheight to 0//雾密度呈指数变化。//摄像机与雾的相对高度越大，这个密度值越小，且最小为0；相对高度越小，雾密度越大，最高为正无穷。//当摄像机的高度比雾高度小时，雾的密度始终大于1，且变化剧烈；反之，雾密度始终小于1， 且随着高度的增加，逐渐衰减为0//GlobalDensity ，高度雾全局密度，通过这个参数来控制整体的密度，人工干预修正曲线//FogHeightFalloff的引入，是为了缩小高度变化的程度，当衰减值为0时，变化程度缩小最大化，所有高度只有同一个密度值，当那个衰减值为2时，加强了高度对密度的影响程度。float FogDensity = GlobalDensity * exp2(-FogHeightFalloff * (View.WorldCameraOrigin.z-0.0));//abs(Falloff) > FLT_EPSILON2 avoid dvide zero//return RayOriginTerms * (abs(Falloff) > FLT_EPSILON2 ? LineIntegral : LineIntegralTaylor);//RayOriginTerms=FogDensity * exp2(-FogHeightFalloff * (CameraWorldPosition.z - FogHeight)) which is FogStruct.ExponentialFogParameters.xreturn FogDensity * (abs(Falloff) > FLT_EPSILON2 ? LineIntegral : LineIntegralTaylor);}

计算指数高度雾+DirectionalLightInscattering

half4 GetExponentialHeightFog(float3 WorldPositionRelativeToCamera, float ExcludeDistance)
{float3 CameraToReceiver = WorldPositionRelativeToCamera;//const float3 WorldObserverOrigin = View.WorldCameraOrigin.xyz;float CameraToReceiverLengthSqr = dot(CameraToReceiver, CameraToReceiver);float CameraToReceiverLengthInv = rsqrt(CameraToReceiverLengthSqr);float CameraToReceiverLength = CameraToReceiverLengthSqr * CameraToReceiverLengthInv;half3 CameraToReceiverNormalized = CameraToReceiver * CameraToReceiverLengthInv;float RayLength = CameraToReceiverLength;float RayDirectionZ = CameraToReceiver.z;float ExponentialHeightLineIntegralShared = CalculateLineIntegralShared(RayDirectionZ);//RayLength 加上距离的影响float ExponentialHeightLineIntegral = ExponentialHeightLineIntegralShared * RayLength;half MinFogOpacity = 0.0;//设置最小不透明度为0.0 观察低处的影响half ExpFogFactor = max(saturate(exp2(-ExponentialHeightLineIntegral)), 0.5);//Shader type 2:DirectionalLightInscattering--------------------------------------------------------------half3 DirectionalLightInscattering = DirectionalInscatteringColor * pow(saturate(dot(CameraToReceiverNormalized, InscatterinLightDirection)), DirectionalInscatteringStrenthFactor);//距离影响因子float DirExponentialHeightLineIntegral = ExponentialHeightLineIntegralShared * max(RayLength - DirectionalInscatteringStartDistance, 0.0f);// Calculate the amount of light that made it through the fog using the transmission equationhalf DirectionalInscatteringFogFactor = saturate(exp2(-DirExponentialHeightLineIntegral));// Final inscattering from the lighthalf3 DirectionalInscattering = DirectionalLightInscattering * (1 - DirectionalInscatteringFogFactor);//-----------------------------------------------------------------------------------------------------------half3 FogColor = (MyFogColor.xyz) * (1 - ExpFogFactor) + DirectionalInscattering;//return half4(0.0, 0.0, 0.0, 1.0);return half4(FogColor, ExpFogFactor);
}

void MainPS(in float2 UV: TEXCOORD0,in float3 ScreenVector : TEXCOORD1,in float4 Position : SV_POSITION,out float4 OutColor : SV_Target0
)
{float DeviceZ = Texture2DSampleLevel(SceneTexturesStruct.SceneDepthTexture, SceneTexturesStruct_SceneDepthTextureSampler, UV, 0).r;// @param DeviceZ value that is stored in the depth buffer (Z/W)// @return SceneDepth (linear in world units, W)float SceneDepth = ConvertFromDeviceZ(DeviceZ); // Fetch the depth buffer Z / W value, solve for Wbool bIsRendered = (DeviceZ != 0.0);float3 WorldPositionRelativeToCamera = ScreenVector.xyz * SceneDepth;//scale xyz ??float4 HeightFogInscatteringAndOpacity = CalculateHeightFog(WorldPositionRelativeToCamera);float LightShaftMask = Texture2DSample(OcclusionTexture, OcclusionSampler, UV).x;HeightFogInscatteringAndOpacity.xyz *= LightShaftMask;if (!bIsRendered){HeightFogInscatteringAndOpacity.rgb = 0;HeightFogInscatteringAndOpacity.a = 1;}OutColor = float4(HeightFogInscatteringAndOpacity.xyz, HeightFogInscatteringAndOpacity.w);//recompileshaders changed
}

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【UE4】指数密度高度雾

shader

计算指数高度雾+DirectionalLightInscattering

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