Unity中Shader裁剪空间推导（在Shader中使用）

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前言

在上一篇文章中，我们推导得出了 透视相机到裁剪空间的转化矩阵

• Unity中Shader裁剪空间推导（透视相机到裁剪空间的转化矩阵）

我们在正交矩阵Shader的基础上，继续测试

• Unity中Shader裁剪空间推导（在Shader中实现）

在这篇文章中，我们在Shader中使用该矩阵测试一下。

• OpenGL
  $\left[\begin{array}{cccc}\frac{2n}{w}& 0& 0& 0\\ 0& \frac{2n}{h}& 0& 0\\ 0& 0& \frac{n+f}{n-f}& \frac{2nf}{n-f}\\ 0& 0& -1& 0\end{array}\right]$
• DirectX
  $\left[\begin{array}{cccc}\frac{2n}{w}& 0& 0& 0\\ 0& \frac{2n}{h}& 0& 0\\ 0& 0& \frac{n}{f-n}& \frac{nf}{f-n}\\ 0& 0& -1& 0\end{array}\right]$

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一、在Shader中使用转化矩阵

1、在顶点着色器中定义转化矩阵

• OpenGL：

M_clipP = float4x4
(
2n/w,0,0,0,
0,2n/h,0,0,
0,0,(n+f)/(n-f),(2nf)/(n-f),
0,0,-1,0
);

• DirectX：

M_clipP = float4x4
(
2n/w,0,0,0,
0,2n/h,0,0,
0,0,n/(f-n),(n*f)/(f-n),
0,0,-1,0
);

2、用 UNITY_NEAR_CLIP_VALUE 区分平台矩阵

• 1为OpenGL
• -1为DirectX

3、定义一个枚举用于区分当前是处于什么相机

[Enum(OrthoGraphic,0,Perspective,1)]_CameraType(“CameraType”,Float) = 0

• 在手动转化矩阵时使用三目运算符来决定使用哪一个矩阵

float4x4 M_clip = _CameraType ? M_clipP : M_clipO;
o.vertexCS = mul(M_clip,float4(vertexVS,1));

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二、我们在DirectX平台下，看看效果

1、正交相机下

2、透视相机下

3、最终代码

//平移变换
//缩放变换
//旋转变换（四维）
//视图空间矩阵
//正交相机视图空间 -> 裁剪空间
Shader "MyShader/URP/P3_7_6"
{Properties{[Header(MainTexx)]_MainTex("MainTex",2D) = "white"{}[Header(Transtion)]_Translate("Translate(XYZ)",Vector) = (0,0,0,0)_Scale("Scale(XYZ)",Vector)= (1,1,1,1)_Rotation("Rotation(XYZ)",Vector) = (0,0,0,0)[Header(View)]_ViewPos("View Pos",vector) = (0,0,0,0)_ViewTarget("View Target",vector) = (0,0,0,0)[Header(Camera)]_CameraParams("Size(X),Near(Y),Far(Z) Ratio(W)",Vector) = (0,0,0,1.777)[Enum(OrthoGraphic,0,Perspective,1)]_CameraType("CameraType",Float) = 0}SubShader{Tags{"PenderPipeline"="UniversalPipeline""RenderType"="Opaque""Queue"="Geometry"}Pass{HLSLPROGRAM#pragma vertex vert#pragma fragment frag#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"struct Attribute{float4 vertexOS : POSITION;float2 uv : TEXCOORD0;};struct Varying{float4 vertexCS : SV_POSITION;float2 uv : TEXCOORD0;};CBUFFER_START(UnityPerMaterial)float4 _Translate;float4 _Scale;float4 _Rotation;float4 _ViewPos;float4 _ViewTarget;float4 _CameraParams;float _CameraType;CBUFFER_ENDTEXTURE2D(_MainTex);SAMPLER(sampler_MainTex);Varying vert (Attribute v){Varying o;o.uv = v.uv;//平移变换float4x4 M_Translate = float4x4(1,0,0,_Translate.x,0,1,0,_Translate.y,0,0,1,_Translate.z,0,0,0,1);v.vertexOS = mul(M_Translate,v.vertexOS);//缩放交换float4x4 M_Scale = float4x4(_Scale.x,0,0,0,0,_Scale.y,0,0,0,0,_Scale.z,0,0,0,0,1);v.vertexOS = mul(M_Scale,v.vertexOS);//旋转变换float4x4 M_rotateX = float4x4(1,0,0,0,0,cos(_Rotation.x),sin(_Rotation.x),0,0,-sin(_Rotation.x),cos(_Rotation.x),0,0,0,0,1);float4x4 M_rotateY = float4x4(cos(_Rotation.y),0,sin(_Rotation.y),0,0,1,0,0,-sin(_Rotation.y),0,cos(_Rotation.y),0,0,0,0,1);float4x4 M_rotateZ = float4x4(cos(_Rotation.z),sin(_Rotation.z),0,0,-sin(_Rotation.z),cos(_Rotation.z),0,0,0,0,1,0,0,0,0,1);v.vertexOS = mul(M_rotateX,v.vertexOS);v.vertexOS = mul(M_rotateY,v.vertexOS);v.vertexOS = mul(M_rotateZ,v.vertexOS);//观察空间矩阵推导//P_view = [W_view] * P_world//P_view = [V_world]^-1 * P_world//P_view = [V_world]^T * P_worldfloat3 ViewZ = normalize(_ViewPos.xyz - _ViewTarget.xyz);float3 ViewY = float3(0,1,0);float3 ViewX = cross(ViewZ,ViewY);ViewY = cross(ViewX,ViewZ);float4x4 M_viewTemp = float4x4(ViewX.x,ViewX.y,ViewX.z,0,ViewY.x,ViewY.y,ViewY.z,0,ViewZ.x,ViewZ.y,ViewZ.z,0,0,0,0,1);float4x4 M_viewTranslate = float4x4(1,0,0,-_ViewPos.x,0,1,0,-_ViewPos.y,0,0,1,-_ViewPos.z,0,0,0,1);float4x4 M_view = mul(M_viewTemp,M_viewTranslate);float3 vertexWS = TransformObjectToWorld(v.vertexOS.xyz);//世界空间转化到观察空间float3 vertexVS = mul(M_view,float4(vertexWS,1)).xyz;//相机参数float h = _CameraParams.x * 2;float w = h * _CameraParams.w;float n = _CameraParams.y;float f = _CameraParams.z;//正交相机投影矩阵//P_Clip = [M_Clip] * P_viewfloat4x4 M_clipO;if(UNITY_NEAR_CLIP_VALUE==-1){//OpenGLM_clipO = float4x4(2/w,0,0,0,0,2/h,0,0,0,0,2/(n - f),(n + f) / (n - f),0,0,0,1);}if(UNITY_NEAR_CLIP_VALUE==1){//DirectXM_clipO = float4x4(2/w,0,0,0,0,2/h,0,0,0,0,1/(f-n),f/(f-n),0,0,0,1);}//透视相机投影矩阵float4x4 M_clipP;if(UNITY_NEAR_CLIP_VALUE==-1){//OpenGLM_clipP = float4x4(2*n/w,0,0,0,0,2*n/h,0,0,0,0,(n+f)/(n-f),(2*n*f)/(n-f),0,0,-1,0);}if(UNITY_NEAR_CLIP_VALUE==1){//DirectXM_clipP = float4x4(2*n/w,0,0,0,0,2*n/h,0,0,0,0,n/(f-n),(n*f)/(f-n),0,0,-1,0);}//手动将观察空间下的坐标转换到裁剪空间下float4x4 M_clip = _CameraType ? M_clipP : M_clipO;o.vertexCS = mul(M_clip,float4(vertexVS,1));//观察空间 转化到 齐次裁剪空间//o.vertexCS = TransformWViewToHClip(vertexVS);//o.vertexCS = TransformObjectToHClip(v.vertexOS.xyz);return o;}half4 frag (Varying i) : SV_Target{float4 mainTex = SAMPLE_TEXTURE2D(_MainTex,sampler_MainTex,i.uv);return mainTex;}ENDHLSL}}
}