Unity中Shader裁剪空间推导（在Shader中使用）

---

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

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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));

---

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_END
            
            TEXTURE2D(_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_world
                float3 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_view
                float4x4 M_clipO;
                if(UNITY_NEAR_CLIP_VALUE==-1)
                {
                    //OpenGL
                    M_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)
                {
                    //DirectX
                    M_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)
                {
                    //OpenGL
                    M_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)
                {
                    //DirectX
                    M_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
        }
    }
}