Ray Marching（一）
主要内容：实现世界坐标下摄像机发出的射线向量
通过分形的Noise实现云朵
1.在unity做ray marching的射线
2.Noise与FBM
3.依据ray的旋转角实现天空
4.天空的其他部分
1.RayMarching射线
求出根据相机fieldOfView与近裁剪面的距离求出近裁剪面四个顶点相对与摄像机的相对向量；
再将四个向量值赋予 后期处理的全屏四边形 的四个顶点上；
这四个顶点会通过shader中的插值，求出在每个片元上的ray向量；
2.Noise与FBM
详细请看：https://blog.csdn.net/candycat1992/article/details/50346469 【冯乐乐】
这里我用的是value noise
float Noise(float2 p)
{
float2 pi = floor(p);
float2 pf = p - pi;
float2 w = pf * pf * (3.0 - 2.0 * pf);
return lerp(lerp(Hash12(pi + float2(0.0, 0.0)), Hash12(pi + float2(1.0, 0.0)), w.x),
lerp(Hash12(pi + float2(0.0, 1.0)), Hash12(pi + float2(1.0, 1.0)), w.x),
w.y);
}
FBM（分形后的Noise）这里加了2D的旋转矩阵 ，并加入了时间移动
float FBM( float2 p ,float time)
{
float f = 0.0;
p+=time;
f += 0.50000*Noise( p ); p = mul(float2x2(0.8,-0.6,0.6,0.8),p)*2.01; p+=time;
f += 0.25000*Noise( p ); p = mul(float2x2(0.8,-0.6,0.6,0.8),p)*2.02; p+=time;
f += 0.12500*Noise( p ); p = mul(float2x2(0.8,-0.6,0.6,0.8),p)*2.03; p+=time;
f += 0.06250*Noise( p ); p = mul(float2x2(0.8,-0.6,0.6,0.8),p)*2.04; p+=time;
f += 0.03100*Noise( p ); p = mul(float2x2(0.8,-0.6,0.6,0.8),p)*2.04; p+=time;
return f/0.984375;
}
3.依据ray的旋转角实现天空
先来看一下利用ray向量各个分形，类似2Duv平铺后的情况 frac(ray.xyz)
来用ps剖切下
所以在描绘天空时，应用ray的xz坐标读取Noise
但天空编成了球形，这不是我们我们想要的。下面把天空变为一个旋在头顶的平面
//cloud
float cos0 = dot(normalize(rd),float3(0,1,0));
float cloudNoise = 0;
float s = 0.5;
for(int i=0;i<3;i++){
float height = 2000 + i * 1000;
float3 pos = height/cos0 * rd;
float2 worldXZ = ro.xz + pos.xz;
cloudNoise += s * FBMRTIME(worldXZ/2000 + i * 500 ,(_Time.y / (1+i*2)) /20);
s*=0.5;
}
cloudNoise = smoothstep(0.4, 0.6, cloudNoise);
代码中的循环，是为了制作三层不同高度的云，第一层2000，每向上一层+1000
并且每层云移动速度也有不同
4.天空其他部分
剩下的问题:代码说话
1.颜色
//skycolor
float3 skyColor= float3(0.2,0.5,0.85)*1.1 - rd.y*rd.y*0.5;
skyColor= lerp( skyColor, 0.85*float3(0.7,0.75,0.85), pow( 1.0-max(rd.y,0.0), 4.0 ) );
skyColor+=sunColor;
2.太阳
// sun
float sundot = clamp(dot(rd,lightDir),0.0,1.0);
float3 sunColor= 0.25*float3(1.0,0.7,0.4)*pow( sundot,5.0 );
sunColor += 0.25*float3(1.0,0.8,0.6)*pow( sundot,64.0 );
sunColor += 0.4*float3(1.0,0.8,0.6)*pow( sundot,512.0 );
3.太密了与地面。太密了：偷懒就用远处的雾来遮住；
方法用ray的y分量的值 lerp 天空/雾/地面的颜色；
//skydown
float3 sky =lerp(skyColor ,float3(1.0,0.95,1.0) , cloudNoise );
sky =lerp(skyColor , sky ,smoothstep(-0.1,0.25,rd.y) ) ;
sky =lerp(float3(0.4,0.4,0.4) , sky ,smoothstep(-0.1,0.1,rd.y) );
图片压缩太厉害出现个大白道
码
1.ray向量的后期
c#脚本
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
[ExecuteInEditMode]
[RequireComponent(typeof(Camera))]
public class RayMarch : MonoBehaviour
{
public float MountainHeight;
public Material material;
//public Transform DirLightTransform;
public Vector3 LightDir;
private Camera MyCamera;
private Transform MyCameraTransform;
//如果不支持material就取消勾选
private void Start(){
if(material==null||material.shader==null||!material.shader.isSupported){
enabled=false;
return;
}else{
MyCamera=GetComponent<Camera>();
}
}
void OnEnalbe(){
//让摄像机产生深度纹理
MyCamera.depthTextureMode |=DepthTextureMode.Depth;
}
[ImageEffectOpaque]
void OnRenderImage(RenderTexture src,RenderTexture dest){
if(material!=null){
SetRay();
Graphics.Blit(src,dest,material);
}else{
Graphics.Blit(src,dest);
}
}
private void SetRay(){
Matrix4x4 fourPoint=Matrix4x4.identity; //角度与弧度的转换 Π 与 0
float fov = MyCamera.fieldOfView;
float near =MyCamera.nearClipPlane;
float aspect=MyCamera.aspect;
float halfHeight = near* Mathf.Tan(fov*0.5f*Mathf.Deg2Rad);
float halfRight = halfHeight * aspect;
Vector3 toHeight = MyCamera.transform.up * halfHeight;
Vector3 toRight = MyCamera.transform.right * halfRight;
Vector3 topLeft = MyCamera.transform.forward*near + toHeight - toRight;
float scale= topLeft.magnitude/near;
topLeft*= scale;
Vector3 topRight=MyCamera.transform.forward*near +toHeight +toRight;
topRight*=scale;
Vector3 bottomLeft=MyCamera.transform.forward*near - toHeight -toRight;
bottomLeft*=scale;
Vector3 bottomRight=MyCamera.transform.forward*near -toHeight +toRight;
bottomRight*=scale;
fourPoint.SetRow(0,bottomLeft);
fourPoint.SetRow(1,bottomRight);
fourPoint.SetRow(2,topRight);
fourPoint.SetRow(3,topLeft);
//Vector4 DirLight=DirLightTransform.eulerAngles;
Vector4 DirLight=LightDir;
material.SetMatrix("_FourRay",fourPoint);
material.SetFloat("_MountainHeight",MountainHeight);
material.SetVector("_LightDir",DirLight);
}
}
shader 天空代码写在ProcessRayMarch（）里
Shader "Hidden/RayMarching"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_MountainHeight("MountainHeight",float)=100
_LightDir("LightDir",vector)=(0,1,0,0)
}
SubShader
{
// No culling or depth
Cull Off ZWrite Off ZTest Always
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
#include "RayTemp.cginc"
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};
struct v2f
{
float4 pos : SV_POSITION;
float2 uv : TEXCOORD0;
float4 Ray:TEXCOORD1;
};
sampler2D _MainTex;
float2 _MainTex_TexelSize;
float4x4 _FourRay;
v2f vert (appdata v)
{
v2f o;
o.pos = UnityObjectToClipPos(v.vertex);
o.uv = v.uv;
int index=0;
if( o.uv.x<0.5 && o.uv.y<0.5){
index = 0 ;
}else if( o.uv.x>0.5 && o.uv.y<0.5){
index = 1;
}else if( o.uv.x>0.5 && o.uv.y>0.5){
index = 2;
}else if( o.uv.x<0.5 && o.uv.y>0.5){
index = 3;
}
#if UNITY_UV_STARTS_AT_TOP
if (_MainTex_TexelSize.y < 0)
index = 3 - index;
#endif
o.Ray = _FourRay[index];
return o;
}
fixed4 frag (v2f i) : SV_Target
{
fixed4 sceneCol=tex2D(_MainTex,i.uv);
float3 ro = _WorldSpaceCameraPos;
float3 rd = normalize(i.Ray.xyz);
return ProcessRayMarch(ro,rd,sceneCol);
}
ENDCG
}
}
}
2.天空shader
float4 ProcessRayMarch(float3 ro,float3 rd,float4 sceneCol){
//data
float3 lightDir=normalize( _LightDir.xyz);
float4 finalColor=float4(0,0,0,1);
//sky-------------------------------------------------------------------------------
//cloud
float cos0 = dot(normalize(rd),float3(0,1,0));
float cloudNoise = 0;
float s = 0.5;
for(int i=0;i<3;i++){
float height = 2000 + i * 1000;
float3 pos = height/cos0 * rd;
float2 worldXZ = ro.xz + pos.xz;
cloudNoise += s * FBMRTIME(worldXZ/2000 + i * 500 ,(_Time.y / (1+i*2))/5 );
s*=0.5;
}
cloudNoise = smoothstep(0.4, 0.6, cloudNoise);
// sun
float sundot = clamp(dot(rd,lightDir),0.0,1.0);
float3 sunColor= 0.25*float3(1.0,0.7,0.4)*pow( sundot,5.0 );
sunColor += 0.25*float3(1.0,0.8,0.6)*pow( sundot,64.0 );
sunColor += 0.4*float3(1.0,0.8,0.6)*pow( sundot,512.0 );
//skycolor
float3 skyColor= float3(0.2,0.5,0.85)*1.1 - rd.y*rd.y*0.5;
skyColor= lerp( skyColor, 0.85*float3(0.7,0.75,0.85), pow( 1.0-max(rd.y,0.0), 4.0 ) );
skyColor+=sunColor;
//skydown
float3 sky =lerp(skyColor ,float3(1.0,0.95,1.0) , cloudNoise );
sky =lerp(skyColor , sky ,smoothstep(-0.1,0.25,rd.y) ) ;
sky =lerp(float3(0.4,0.4,0.4) , sky ,smoothstep(-0.1,0.1,rd.y) );
return float4(sky,1.);
}
