1.简介
这是一个通过在角色骨骼上绑定虚拟胶囊体拟合出胶囊近似AO环境光遮蔽的效果，
当角色处于阴影中时，CapsuleAO的效果比较明显。当角色在露天环境中，效果较弱。
下面是其他游戏里截图的效果，以做参考：
不同项目有不同的实现，UE4中也有类似实现，叫做Capsule Shadow，这里不多做介绍：
2.CapsuleAO实现尝试
首先用自己的思路实现一下，首先参考了IQ大神的SphereAO：
https://www.shadertoy.com/view/4djSDy
抛开公式的话，其实就是一个点光源的做法，然后把颜色改成黑色加上函数系数进行调节，使其更接近AO的感觉。
这是尝试实现的效果：
实现时要将球体变为胶囊，要在胶囊的长度轴上计算投影。投影完后对投影长度进行Clamp约束，约束后的两个端点
和周围像素进行Distance计算，这样直接就是胶囊的效果了，而不是圆柱。做了个简单的图：
具体见代码。
Shader：
Shader "Unlit/CapsuleAOShader" { Properties { _Adjust("Adjust", float) = 2 _CapsuleRadius("Capsule Radius", float) = 0.3 _DistanceFix("Distance Fix", float) = 0.3 } SubShader { Tags { "RenderType"="Opaque" } Pass { CGPROGRAM #pragma vertex vert #pragma fragment frag #include "UnityCG.cginc" struct appdata { float4 vertex : POSITION; float2 uv : TEXCOORD0; }; struct v2f { float2 uv : TEXCOORD0; float4 vertex : SV_POSITION; float3 wPos : TEXCOORD2; }; float4 _PlanePos; float4 _PlaneNormal; float4 _CapsuleP0; float4 _CapsuleP1; float _Adjust; float _CapsuleRadius; float _DistanceFix; float3 Formula(float3 sphP0, float3 sphP1, float length, float radius, float3 comparePoint) { float3 norm1 = normalize(sphP1 - sphP0); float3 relativeComparePoint = comparePoint-sphP0; float3 projValue = dot(relativeComparePoint, norm1); float x = clamp(projValue, -length, length); float3 projPoint = sphP0 + x * norm1; float3 norm2 = normalize(comparePoint - projPoint); return projPoint + norm2 * radius; } float3 DistanceFix(float3 distancePoint, float wPos, float3 norm, float distanceFix) { return distancePoint + norm * distanceFix; } float Occlusion(float3 pos, float3 nor, float3 sphP0, float3 sphP1) { float3 finalPoint = Formula(sphP0, sphP1, distance(sphP1,sphP0), _CapsuleRadius, pos);/*Add*/ finalPoint = DistanceFix(finalPoint, pos, nor, _DistanceFix);/*Add*/ float3 di = finalPoint - pos; float l = length(di); float nl = dot(nor, di / l); float h = l / 0.5; float h2 = h * h; float k2 = 1.0 - h2 * nl*nl; float res = pow(clamp(0.5*(nl*h + 1.0) / h2, 0.0, 1.0), 1.5); return res; } v2f vert (appdata v) { v2f o = (v2f)0; o.vertex = UnityObjectToClipPos(v.vertex); o.uv = v.uv; o.wPos = mul(unity_ObjectToWorld, v.vertex).xyz; return o; } fixed4 frag (v2f i) : SV_Target { float occ0 = Occlusion(i.wPos, _PlaneNormal.xyz, _CapsuleP0.xyz, _CapsuleP1.xyz); return 1.0 - occ0; } ENDCG } } }
c#部分，控制胶囊的传入，与球体不同；胶囊需要一个长度向量信息表示长度轴的朝向：
using System.Collections; using System.Collections.Generic; using UnityEngine; public class CapsuleAOParamUpdate : MonoBehaviour { public Transform capsuleP0; public Transform capsuleP1; Material mMaterial; private void Update() { mMaterial = GetComponent<MeshRenderer>().sharedMaterial; mMaterial.SetVector("_PlanePos", transform.position); mMaterial.SetVector("_PlaneNormal", transform.up); mMaterial.SetVector("_CapsuleP0", new Vector4(capsuleP0.position.x, capsuleP0.position.y, capsuleP0.position.z, 1f)); mMaterial.SetVector("_CapsuleP1", new Vector4(capsuleP1.position.x, capsuleP1.position.y, capsuleP1.position.z, 1f)); } }
3.Capsule Shadow实现尝试
看了下UE里的实现代码，比较复杂。这部分自己处理比较简单。
先看最终效果(支持非平面表面,光照方向改变,但某些光照角度有一定穿帮感)：
首先，以主光平行光的方向作为投影平面，在shader的frag里得到地面每个像素世界坐标时，
将像素位置，胶囊位置，胶囊方向向量等都投影到平面上进行计算。
大致如下图：
胶囊体需要两个参数，以确定胶囊方向。根据投影后的胶囊方向和地面法线位置，得到叉乘位置，然后可以作为x,y坐标采样贴图。
采样贴图虽然效果好些，但开销较高，所以也可以自己去拟合。
接着混合3个权重信息：
- 对平行光的相反方向做一个点乘处理，防止反方向上也被映射上阴影(FadeDirectionWeight)。
- 对主要投影区域做一个权重系数，让只有被投影地面上有阴影图案(MaskWeight)。
- 将投影前的地面世界空间坐标和投影前的胶囊位置做一个权重，让阴影有一个深到浅的渐变效果(FadeWeight)。
最后将所有权重混合：
return shadowCol * maskWeight * fadeWeight * faceDirectionWeight;
最后上代码。
shader部分：
Shader "Unlit/CapsuleShadowShader" { Properties { _MainShapeTex ("Main Shape Tex (RGB)", 2D) = "white" {} _UvOffset("Uv Offset", vector) = (0.0, 0.0, 0.0, 0.0) _ShadowScaleFactor("Shadow Scale Factor", float) = 1.0 _FadeWeightFactor("Fade Weight Factor", float) = 10.0 _FadeDirectionFactor("Fade Direction Factor", float) = 1.0 } SubShader { Tags { "RenderType"="Opaque" } Pass { CGPROGRAM #pragma vertex vert #pragma fragment frag #include "UnityCG.cginc" struct appdata { float4 vertex : POSITION; float2 uv : TEXCOORD0; }; struct v2f { float2 uv : TEXCOORD0; float4 vertex : SV_POSITION; float3 wPos : TEXCOORD2; }; uniform float4 _LightDirectionVector; uniform float4 _CapsulePos1; uniform float4 _CapsulePos2; uniform float4 _CapsulePos3; uniform float4 _CapsulePos4; uniform float4 _CapsulePos5; uniform float4 _CapsulePos6; uniform float4 _CapsulePos7; uniform float4 _CapsulePos8; uniform float4 _CapsulePos9; uniform float4 _CapsulePos10; uniform float4 _CapsulePos11; uniform float4 _CapsulePos12; uniform float4 _CapsulePos13; uniform float4 _CapsulePos14; sampler2D _MainShapeTex; float4 _UvOffset; float _ShadowScaleFactor; float _FadeWeightFactor; float _FadeDirectionFactor; v2f vert (appdata v) { v2f o = (v2f)0; o.vertex = UnityObjectToClipPos(v.vertex); o.uv = v.uv; o.wPos = mul(unity_ObjectToWorld, v.vertex).xyz; return o; } half3 ProjectOnPlane(half3 vec, half3 planeNormal) { float num = dot(planeNormal, planeNormal); float num2 = dot(vec, planeNormal); return half3(vec.x - planeNormal.x * num2 / num, vec.y - planeNormal.y * num2 / num, vec.z - planeNormal.z * num2 / num); } half CapsuleShadow(float3 capsulePos, float3 capsulePosDirectVec, float3 wPos) { half faceDirectionWeight = max(_FadeDirectionFactor, dot(normalize(capsulePos - wPos), _WorldSpaceLightPos0.xyz)); half fadeDistance = distance(wPos, capsulePos); half fadeWeight = (1.0/distance(wPos, capsulePos)) * _FadeWeightFactor; half3 proj = ProjectOnPlane(wPos, _WorldSpaceLightPos0.xyz); half3 centerProj = ProjectOnPlane(capsulePos, _WorldSpaceLightPos0.xyz); half3 centerVectorProj = ProjectOnPlane(capsulePosDirectVec, _WorldSpaceLightPos0.xyz); half3 dir1 = normalize(centerVectorProj - centerProj); half3 dir2 = normalize(cross(dir1, _WorldSpaceLightPos0.xyz)); half x = dot(proj - centerProj, dir1) * _UvOffset.z + _UvOffset.x; half y = dot(proj - centerProj, dir2) * _UvOffset.w + _UvOffset.y; half shadowCol = tex2D(_MainShapeTex, half2(x, y)).r; half maskWeight = saturate(distance(proj, centerProj) / _ShadowScaleFactor); maskWeight = max(0.4, maskWeight); return shadowCol * maskWeight * fadeWeight * faceDirectionWeight; } fixed4 frag (v2f i) : SV_Target { half col = CapsuleShadow(_CapsulePos1, _LightDirectionVector, i.wPos); col = max(col, CapsuleShadow(_CapsulePos2, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos3, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos4, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos5, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos6, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos7, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos8, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos9, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos10, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos11, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos12, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos13, _LightDirectionVector, i.wPos)); col = max(col, CapsuleShadow(_CapsulePos14, _LightDirectionVector, i.wPos)); return lerp(0.5, 0.0, col); } ENDCG } } }
c#部分:
using System.Collections; using System.Collections.Generic; using UnityEngine; public class CapsuleAOParamUpdate : MonoBehaviour { public Transform capsuleHead; public Transform capsuleBody1; public Transform capsuleBody2; public Transform capsuleBody3; public Transform capsuleLeftArm1; public Transform capsuleLeftArm2; public Transform capsuleLeftArm3; public Transform capsuleRightArm1; public Transform capsuleRightArm2; public Transform capsuleRightArm3; public Transform capsuleLeftLeg1; public Transform capsuleLeftLeg2; public Transform capsuleLeftLeg3; public Transform capsuleRightLeg1; public Transform capsuleRightLeg2; public Transform capsuleRightLeg3; public Transform lightDirectionVector; private Material mMaterial; private void Update() { mMaterial = GetComponent<MeshRenderer>().sharedMaterial; if (capsuleHead) mMaterial.SetVector("_CapsulePos1", capsuleHead.position); if (capsuleBody1) mMaterial.SetVector("_CapsulePos2", capsuleBody1.position); if (capsuleBody2) mMaterial.SetVector("_CapsulePos2", capsuleBody2.position); if (capsuleBody3) mMaterial.SetVector("_CapsulePos2", capsuleBody3.position); if (capsuleLeftArm1) mMaterial.SetVector("_CapsulePos3", capsuleLeftArm1.position); if (capsuleLeftArm2) mMaterial.SetVector("_CapsulePos4", capsuleLeftArm2.position); if (capsuleLeftArm3) mMaterial.SetVector("_CapsulePos5", capsuleLeftArm3.position); if (capsuleRightArm1) mMaterial.SetVector("_CapsulePos6", capsuleRightArm1.position); if (capsuleRightArm2) mMaterial.SetVector("_CapsulePos7", capsuleRightArm2.position); if (capsuleRightArm3) mMaterial.SetVector("_CapsulePos8", capsuleRightArm3.position); if (capsuleLeftLeg1) mMaterial.SetVector("_CapsulePos9", capsuleLeftLeg1.position); if (capsuleLeftLeg2) mMaterial.SetVector("_CapsulePos10", capsuleLeftLeg2.position); if (capsuleLeftLeg3) mMaterial.SetVector("_CapsulePos11", capsuleLeftLeg3.position); if (capsuleRightLeg1) mMaterial.SetVector("_CapsulePos12", capsuleRightLeg1.position); if (capsuleRightLeg2) mMaterial.SetVector("_CapsulePos13", capsuleRightLeg2.position); if (capsuleRightLeg3) mMaterial.SetVector("_CapsulePos14", capsuleRightLeg3.position); mMaterial.SetVector("_LightDirectionVector", lightDirectionVector.position); } }
4.总结
这篇文章以学习为主，就不提供下载工程了。具体使用还需自行开发。
若该方案需要在项目中的落地，我做如下建议：
1.不要一次性在shader里传入所有胶囊，可以分成多个pass来做，也可以放到屏幕blit里去做，或者先画到一张临时RT里。
2.当角色暴露在强光下，基本看不出CapsuleAO效果，当角色在阴影中或处于柔和光照环境下，才会有明显的CapsuleAO表现。
3.也可以只有主角有CapsuleAO效果。