【风宇冲】Unity3D教程宝典之Shader篇：第二十七讲Geometry Shaders

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                       Shader第二十七讲 GeometryShaders

本文
Geometry Shader简称为g
Vertex Shader简称为v
Fragment Shader简称为f

Geometry Shader是继Vertex Shader和Fragment Shader之后，由Shader Model4（第四代显卡着色架构）正式引入的第三个着色器。  性能差因为不像V和F那样高度并行.

 Geometry Shader是vertex和pixel之间的一个optional的stage.
V的功能是处理顶点，G是处理图元，最后光栅化后传给F. 通俗理解：G是用来处理三角形的
V的输出 传给 G 作为输入，G 处理完成后，G的输出 传给 F作为输入
G输出的是最后的齐次裁剪空间，也就是经过mvp。


使用步骤：
(1)  使用声明
#pragma geometry GS_Main

(2) 函数
【设置输出最大顶点数量】
函数前添加[maxvertexcount(4)]

【输入】的图元
必须添加以下前缀之一，例如添加Point就是指这个三角形被当作一个point读取第一个点。（注意如果处理一个quad,2个三角形，所以实际上只有2个点，而不是全部4个顶点）
point line triangle lineadj triangleadj
【输出】必须加inout前缀， triStream.Append(pIn);
PointStream
LineStream
TriangleStream

1.                 [maxvertexcount(11)]
2.                 void GS_Main(triangle GS_INPUT p[3], inout TriangleStream triStream)
3.                 {
4.                     for(int i=0;i<<font face="Consolas"> 3;i++)
5.                     {
6.                         FS_INPUT f;
7.                         f.pos = p[i].pos;
8.                         f.tex0 = p[i].tex0;
9.                         triStream.Append(f);
10.                     }
11.                     triStream.RestartStrip();
12.                 }

[例：不处理]

本例实现的效果和普通的Vertex/Fragment Shader效果一样。

1. Shader "Custom/0same" 
2. {
3.     Properties 
4.     {
5.           _MainTex ("Particle Texture", 2D) = "white" {}
6.     }
7.     SubShader 
8.     {
9.         Pass
10.         {
11.             Tags { "RenderType"="Opaque" }
12.         
13.             CGPROGRAM
14.                 #pragma target 5.0
15.                 #pragma vertex VS_Main
16.                 #pragma fragment FS_Main
17.                 #pragma geometry GS_Main
18.                 #include "UnityCG.cginc" 
19.                 sampler2D   _MainTex;              
20.                 float4      _MainTex_ST;   
21.                 struct GS_INPUT
22.                 {
23.                     float4    pos        : POSITION;
24.                     float3    normal    : NORMAL;
25.                     float2  tex0    : TEXCOORD0;
26.                 };
27.                 struct FS_INPUT
28.                 {
29.                     float4    pos        : SV_POSITION;
30.                     float2  tex0    : TEXCOORD0;
31.                 };
32.                 //step1
33.                 GS_INPUT VS_Main(appdata_base v)
34.                 {
35.                     GS_INPUT output = (GS_INPUT)0;
36.                     output.pos =  mul(UNITY_MATRIX_MVP,v.vertex);
37.                     output.tex0 = TRANSFORM_TEX(v.texcoord,_MainTex);
38.                     output.normal = v.normal;
39.                     return output;
40.                 }
41.                 //step2
42.                 [maxvertexcount(11)]
43.                 void GS_Main(triangle GS_INPUT p[3], inout TriangleStream triStream)
44.                 {
45.                     for(int i=0;i <<font face="Consolas"> 3;i++)
46.                     {
47.                         FS_INPUT f;
48.                         f.pos = p[i].pos;
49.                         f.tex0 = p[i].tex0;
50.                         triStream.Append(f);
51.                     }
52.                     triStream.RestartStrip();
53.                 }
54.                 //step3
55.                 float4 FS_Main(FS_INPUT i) : COLOR
56.                 {
57.                     fixed4 col = tex2D(_MainTex, i.tex0);   
58.                     return col;
59.                 }
60.             ENDCG
61.         }
62.     } 
63. }
64. 
    

[例一：显示模型顶点]

1. Shader "Custom/ShowDots" 
2. {
3.     Properties 
4.     {
5.     }
6.     SubShader 
7.     {
8.         Pass
9.         {
10.             Tags { "RenderType"="Opaque" }
11.             LOD 200
12.         
13.             CGPROGRAM
14.                 #pragma target 5.0
15.                 #pragma vertex VS_Main
16.                 #pragma fragment FS_Main
17.                 #pragma geometry GS_Main
18.                 #include "UnityCG.cginc" 
19.                 struct GS_INPUT
20.                 {
21.                     float4    pos        : POSITION;
22.                     float3    normal    : NORMAL;
23.                     float2  tex0    : TEXCOORD0;
24.                 };
25.                 struct FS_INPUT
26.                 {
27.                     float4    pos        : POSITION;
28.                     float2  tex0    : TEXCOORD0;
29.                 };
30.                 //step1
31.                 GS_INPUT VS_Main(appdata_base v)
32.                 {
33.                     GS_INPUT output = (GS_INPUT)0;
34.                     output.pos =  mul(_Object2World, v.vertex);
35.                     output.normal = v.normal;
36.                     output.tex0 = float2(0, 0);
37.                     return output;
38.                 }
39.                 //step2
40.                 [maxvertexcount(4)]
41.                 void GS_Main(point GS_INPUT p[1], inout PointStream triStream)
42.                 {
43.                     float4 v = float4(p[0].pos.x,p[0].pos.y,p[0].pos.z,1.0f);
44.                     //can move up a little bit
45.                     //    v = v + float4(0,1,0,0);
46.                     float4x4 vp = mul(UNITY_MATRIX_MVP, _World2Object);
47.                     FS_INPUT pIn;
48.                     pIn.pos = mul(vp, v);
49.                     pIn.tex0 = float2(0.0f, 0.0f);
50.                     triStream.Append(pIn);
51.                 }
52.                 //step3
53.                 float4 FS_Main(FS_INPUT input) : COLOR
54.                 {
55.                     return float4(1,1,1,1);
56.                 }
57.             ENDCG
58.         }
59.     } 
60. }

因为每个三角形只读一个点，如果改成如下，就每个点都显示了。

Shader "Custom/1ShowPoints2" 
{
    Properties 
    {
    }

    SubShader 
    {
        Pass
        {
            Tags { "RenderType"="Opaque" }
        
            CGPROGRAM
                #pragma target 5.0
                #pragma vertex VS_Main
                #pragma fragment FS_Main
                #pragma geometry GS_Main
                #include "UnityCG.cginc" 

                struct GS_INPUT
                {
                    float4    pos        : POSITION;
                    float3    normal    : NORMAL;
                    float2  tex0    : TEXCOORD0;
                };

                struct FS_INPUT
                {
                    float4    pos        : POSITION;
                    float2  tex0    : TEXCOORD0;
                };


                //step1
                GS_INPUT VS_Main(appdata_base v)
                {
                    GS_INPUT output = (GS_INPUT)0;

                    output.pos =  v.vertex;
                    output.normal = v.normal;
                    output.tex0 = float2(0, 0);
                    return output;
                }

                //step2
                [maxvertexcount(11)]
                void GS_Main(triangle GS_INPUT p[3], inout PointStream triStream)
                {
                    for(int i=0;i<<fontface="Consolas"> 3;i++)
                    {
                        float4 v = float4(p[i].pos.x,p[i].pos.y,p[i].pos.z,1.0f);
                        float4x4 vp = mul(UNITY_MATRIX_MVP, _World2Object);
                        FS_INPUT pIn;
                        pIn.pos = mul(UNITY_MATRIX_MVP, v);
                        pIn.tex0 = float2(0.0f, 0.0f);
                        triStream.Append(pIn);
                    }
                }

                //step3
                float4 FS_Main(FS_INPUT input) : COLOR
                {
                    return float4(1,1,1,1);
                }
            ENDCG
        }
    } 
}

[例二：模型每个顶点显示一个公告板]

Shader "Custom/2Billboard" 
{
    Properties 
    {
        _SpriteTex ("Base (RGB)", 2D) = "white" {}
        _Size ("Size", Range(0, 3)) = 0.5
    }

    SubShader 
    {
        Pass
        {
            Tags { "RenderType"="Opaque" }
            LOD 200
        
            CGPROGRAM
                #pragma target 5.0
                #pragma vertex VS_Main
                #pragma fragment FS_Main
                #pragma geometry GS_Main
                #include "UnityCG.cginc" 

                struct GS_INPUT
                {
                    float4    pos        : POSITION;
                    float3    normal    : NORMAL;
                    float2  tex0    : TEXCOORD0;
                };

                struct FS_INPUT
                {
                    float4    pos        : POSITION;
                    float2  tex0    : TEXCOORD0;
                };

                float _Size;
                float4x4 _VP;
                Texture2D _SpriteTex;
                SamplerState sampler_SpriteTex;

                GS_INPUT VS_Main(appdata_base v)
                {
                    GS_INPUT output = (GS_INPUT)0;

                    output.pos =  mul(_Object2World, v.vertex);
                    output.normal = v.normal;
                    output.tex0 = float2(0, 0);

                    return output;
                }

                [maxvertexcount(4)]
                void GS_Main(point GS_INPUT p[1], inout TriangleStream triStream)
                {
                    float3 up = float3(0, 1, 0);
                    float3 look = _WorldSpaceCameraPos - p[0].pos;
                    look.y = 0;
                    look = normalize(look);
                    float3 right = cross(up, look);
                    
                    float halfS = 0.5f * _Size;
                            
                    float4 v[4];
                    v[0] = float4(p[0].pos + halfS * right - halfS * up, 1.0f);
                    v[1] = float4(p[0].pos + halfS * right + halfS * up, 1.0f);
                    v[2] = float4(p[0].pos - halfS * right - halfS * up, 1.0f);
                    v[3] = float4(p[0].pos - halfS * right + halfS * up, 1.0f);

                    float4x4 vp = mul(UNITY_MATRIX_MVP, _World2Object);
                    FS_INPUT pIn;
                    pIn.pos = mul(vp, v[0]);
                    pIn.tex0 = float2(1.0f, 0.0f);
                    triStream.Append(pIn);

                    pIn.pos =  mul(vp, v[1]);
                    pIn.tex0 = float2(1.0f, 1.0f);
                    triStream.Append(pIn);

                    pIn.pos =  mul(vp, v[2]);
                    pIn.tex0 = float2(0.0f, 0.0f);
                    triStream.Append(pIn);

                    pIn.pos =  mul(vp, v[3]);
                    pIn.tex0 = float2(0.0f, 1.0f);
                    triStream.Append(pIn);
                }

                float4 FS_Main(FS_INPUT input) : COLOR
                {
                    return _SpriteTex.Sample(sampler_SpriteTex, input.tex0);
                }

            ENDCG
        }
    } 
}

[例三：输出金字塔]

1. Shader "Custom/3Pyramid" 
2. {
3.     Properties
4.     {
5.         _MainTex ("Particle Texture", 2D) = "white" {}
6.         _Explode ("Explode factor", Range(0.0, 4.0)) = 1.0
7.     }
8.    
9.     SubShader
10.     {
11.         Pass
12.         {          
13.             CGPROGRAM
14.                 #pragma target 5.0
15.            
16.                 #pragma vertex vert
17.                 #pragma geometry geom
18.                 #pragma fragment frag
19.            
20.                 #include "UnityCG.cginc"
21.                    
22.                 sampler2D   _MainTex;              
23.                 float4      _MainTex_ST;           
24.                 float       _Explode;
25.                 float4x4    _ViewMatrix;
26.                                
27.                 struct VS_INPUT
28.                 {
29.                     float4 Pos  : POSITION;        
30.                     float3 Norm : NORMAL;          
31.                     float2 Tex  : TEXCOORD0;        
32.                 };
33.  
34.                 // GEOMETRY
35.                 struct GSPS_INPUT
36.                 {                          
37.                     float4 Pos  : SV_POSITION;
38.                     float3 Norm : TEXCOORD0;
39.                     float2 Tex  : TEXCOORD1;
40.                 };
41.                                
42.                 // Vertex Shader
43.                 GSPS_INPUT vert( VS_INPUT input )
44.                 {
45.                     GSPS_INPUT output = (GSPS_INPUT)0;
46.                    
47.                     output.Pos  = input.Pos;  // mul( float4(input.Pos,1), _Object2World);  // mul( float4(input.Pos,1), World );
48.                     output.Norm = input.Norm; // mul(input.Norm, (float3x3)_Object2World ); // mul( input.Norm, (float3x3)World );
49.                     output.Tex  = TRANSFORM_TEX(input.Tex, _MainTex);  // input.Tex;
50.                                    
51.                     return output;
52.                 }
53.  
54.                 // Geometry Shader
55.                 [maxvertexcount(12)]
56.                 void geom( triangle GSPS_INPUT input[3], inout TriangleStream outStream )
57.                 {
58.                     GSPS_INPUT output;
59.  
60.                     // Calculate the face normal
61.                     float3 faceEdgeA = input[1].Pos - input[0].Pos;
62.                     float3 faceEdgeB = input[2].Pos - input[0].Pos;
63.                     float3 faceNormal = normalize( cross(faceEdgeA, faceEdgeB) );
64.                     float3 ExplodeAmt = faceNormal*_Explode;
65.                    
66.                     // Calculate the face center                 
67.                     float3 centerPos = (input[0].Pos.xyz + input[1].Pos.xyz + input[2].Pos.xyz)/3.0;
68.                     float2 centerTex = (input[0].Tex + input[1].Tex + input[2].Tex)/3.0;
69.                     centerPos += faceNormal*_Explode;                  
70.                
71.                     // Output the pyramid          
72.                     for( int i=0; i<<fontface="Consolas"> 3; i++ )
73.                     {
74.                         output.Pos = input[i].Pos + float4(ExplodeAmt,0);                                                  
75.                         output.Pos = mul(UNITY_MATRIX_MVP, output.Pos);
76.                         output.Norm = input[i].Norm;
77.                         output.Tex = input[i].Tex;
78.                         outStream.Append( output );
79.                        
80.                         int iNext = (i+1)%3;
81.                         output.Pos = input[iNext].Pos + float4(ExplodeAmt,0);
82.                         output.Pos = mul(UNITY_MATRIX_MVP, output.Pos);
83.                         output.Norm = input[iNext].Norm;
84.                         output.Tex = input[iNext].Tex;
85.                         outStream.Append( output );
86.                        
87.                         output.Pos = float4(centerPos,1) + float4(ExplodeAmt,0);
88.                         output.Pos = mul(UNITY_MATRIX_MVP, output.Pos);                  
89.                         output.Norm = faceNormal;
90.                         output.Tex = centerTex;
91.                         outStream.Append( output );
92.                        
93.                         outStream.RestartStrip();
94.                     }
95.                    
96.                     for( int i=2; i>=0; i-- )
97.                     {
98.                         output.Pos = input[i].Pos + float4(ExplodeAmt,0);
99.                         output.Pos = mul(UNITY_MATRIX_MVP, output.Pos);
100.                         output.Norm = -input[i].Norm;
101.                         output.Tex = input[i].Tex;
102.                         outStream.Append( output );
103.                     }
104.                     outStream.RestartStrip();
105.                 }
106.                
107.                
108.                 // FRAG
109.                 fixed4 frag (GSPS_INPUT i ) : COLOR0
110.                 {                  
111.                     fixed4 col = tex2D(_MainTex, i.Tex);   
112.                     return col;
113.                 }      
114.             ENDCG          
115.         }
116.     }
117.     Fallback Off
118. }

参考：

http://forum.unity3d.com/threads/geometry-shaders.156553/

http://forum.unity3d.com/threads/is-it-possible-to-use-geometry-shader-with-surface-shaders.164905/

http://msdn.microsoft.com/en-us/library/windows/desktop/bb205122(v=vs.85).aspx

http://blog.csdn.net/pizi0475/article/details/7795429