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 Model 4（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
#pragmageometryGS_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);
PointStreamLineStreamTriangleStream
[maxvertexcount(11)]
voidGS_Main(triangleGS_INPUTp[3],inoutTriangleStreamtriStream)
{
for(inti=0;i <3;i++)
{
FS_INPUTf;
f.pos=p[i].pos;
f.tex0=p[i].tex0;
triStream.Append(f);
}
triStream.RestartStrip();
}
[例：不处理]
本例实现的效果和普通的Vertex/Fragment Shader效果一样。
Shader"Custom/0same"
{
Properties
{
_MainTex("ParticleTexture",2D)="white"{}
}
SubShader
{
Pass
{
Tags{"RenderType"="Opaque"}
CGPROGRAM
#pragmatarget5.0
#pragmavertexVS_Main
#pragmafragmentFS_Main
#pragmageometryGS_Main
#include"UnityCG.cginc"
sampler2D_MainTex;
float4_MainTex_ST;
structGS_INPUT
{
float4pos:POSITION;
float3normal:NORMAL;
float2tex0:TEXCOORD0;
};
structFS_INPUT
{
float4pos:SV_POSITION;
float2tex0:TEXCOORD0;
};
//step1
GS_INPUTVS_Main(appdata_basev)
{
GS_INPUToutput=(GS_INPUT)0;
output.pos=mul(UNITY_MATRIX_MVP,v.vertex);
output.tex0=TRANSFORM_TEX(v.texcoord,_MainTex);
output.normal=v.normal;
returnoutput;
}
//step2
[maxvertexcount(11)]
voidGS_Main(triangleGS_INPUTp[3],inoutTriangleStreamtriStream)
{
for(inti=0;i<3;i++)
{
FS_INPUTf;
f.pos=p[i].pos;
f.tex0=p[i].tex0;
triStream.Append(f);
}
triStream.RestartStrip();
}
//step3
float4FS_Main(FS_INPUTi):COLOR
{
fixed4col=tex2D(_MainTex,i.tex0);
returncol;
}
ENDCG
}
}
}
[例一：显示模型顶点]
Shader"Custom/ShowDots"
{
Properties
{
}
SubShader
{
Pass
{
Tags{"RenderType"="Opaque"}
LOD200
CGPROGRAM
#pragmatarget5.0
#pragmavertexVS_Main
#pragmafragmentFS_Main
#pragmageometryGS_Main
#include"UnityCG.cginc"
structGS_INPUT
{
float4pos:POSITION;
float3normal:NORMAL;
float2tex0:TEXCOORD0;
};
structFS_INPUT
{
float4pos:POSITION;
float2tex0:TEXCOORD0;
};
//step1
GS_INPUTVS_Main(appdata_basev)
{
GS_INPUToutput=(GS_INPUT)0;
output.pos=mul(_Object2World,v.vertex);
output.normal=v.normal;
output.tex0=float2(0,0);
returnoutput;
}
//step2
[maxvertexcount(4)]
voidGS_Main(pointGS_INPUTp[1],inoutPointStreamtriStream)
{
float4v=float4(p[0].pos.x,p[0].pos.y,p[0].pos.z,1.0f);
//canmoveupalittlebit
//v=v+float4(0,1,0,0);
float4x4vp=mul(UNITY_MATRIX_MVP,_World2Object);
FS_INPUTpIn;
pIn.pos=mul(vp,v);
pIn.tex0=float2(0.0f,0.0f);
triStream.Append(pIn);
}
//step3
float4FS_Main(FS_INPUTinput):COLOR
{
returnfloat4(1,1,1,1);
}
ENDCG
}
}
}
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
#pragmatarget5.0
#pragmavertexVS_Main
#pragmafragmentFS_Main
#pragmageometryGS_Main
#include"UnityCG.cginc"
structGS_INPUT
{
float4pos:POSITION;
float3normal:NORMAL;
float2tex0:TEXCOORD0;
};
structFS_INPUT
{
float4pos:POSITION;
float2tex0:TEXCOORD0;
};
//step1
GS_INPUTVS_Main(appdata_basev)
{
GS_INPUToutput=(GS_INPUT)0;
output.pos=v.vertex;
output.normal=v.normal;
output.tex0=float2(0,0);
returnoutput;
}
//step2
[maxvertexcount(11)]
voidGS_Main(triangleGS_INPUTp[3],inoutPointStreamtriStream)
{
for(inti=0;i<3;i++)
{
float4v=float4(p[i].pos.x,p[i].pos.y,p[i].pos.z,1.0f);
float4x4vp=mul(UNITY_MATRIX_MVP,_World2Object);
FS_INPUTpIn;
pIn.pos=mul(UNITY_MATRIX_MVP,v);
pIn.tex0=float2(0.0f,0.0f);
triStream.Append(pIn);
}
}
//step3
float4FS_Main(FS_INPUTinput):COLOR
{
returnfloat4(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"}
LOD200
CGPROGRAM
#pragmatarget5.0
#pragmavertexVS_Main
#pragmafragmentFS_Main
#pragmageometryGS_Main
#include"UnityCG.cginc"
structGS_INPUT
{
float4pos:POSITION;
float3normal:NORMAL;
float2tex0:TEXCOORD0;
};
structFS_INPUT
{
float4pos:POSITION;
float2tex0:TEXCOORD0;
};
float_Size;
float4x4_VP;
Texture2D_SpriteTex;
SamplerStatesampler_SpriteTex;
GS_INPUTVS_Main(appdata_basev)
{
GS_INPUToutput=(GS_INPUT)0;
output.pos=mul(_Object2World,v.vertex);
output.normal=v.normal;
output.tex0=float2(0,0);
returnoutput;
}
[maxvertexcount(4)]
voidGS_Main(pointGS_INPUTp[1],inoutTriangleStreamtriStream)
{
float3up=float3(0,1,0);
float3look=_WorldSpaceCameraPos-p[0].pos;
look.y=0;
look=normalize(look);
float3right=cross(up,look);
floathalfS=0.5f*_Size;
float4v[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);
float4x4vp=mul(UNITY_MATRIX_MVP,_World2Object);
FS_INPUTpIn;
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);
}
float4FS_Main(FS_INPUTinput):COLOR
{
return_SpriteTex.Sample(sampler_SpriteTex,input.tex0);
}
ENDCG
}
}
}
[例三：输出金字塔]
Shader"Custom/3Pyramid"
{
Properties
{
_MainTex("ParticleTexture",2D)="white"{}
_Explode("Explodefactor",Range(0.0,4.0))=1.0
}
SubShader
{
Pass
{
CGPROGRAM
#pragmatarget5.0
#pragmavertexvert
#pragmageometrygeom
#pragmafragmentfrag
#include"UnityCG.cginc"
sampler2D_MainTex;
float4_MainTex_ST;
float_Explode;
float4x4_ViewMatrix;
structVS_INPUT
{
float4Pos:POSITION;
float3Norm:NORMAL;
float2Tex:TEXCOORD0;
};
//GEOMETRY
structGSPS_INPUT
{
float4Pos:SV_POSITION;
float3Norm:TEXCOORD0;
float2Tex:TEXCOORD1;
};
//VertexShader
GSPS_INPUTvert(VS_INPUTinput)
{
GSPS_INPUToutput=(GSPS_INPUT)0;
output.Pos=input.Pos;//mul(float4(input.Pos,1),_Object2World);//mul(float4(input.Pos,1),World);
output.Norm=input.Norm;//mul(input.Norm,(float3x3)_Object2World);//mul(input.Norm,(float3x3)World);
output.Tex=TRANSFORM_TEX(input.Tex,_MainTex);//input.Tex;
returnoutput;
}
//GeometryShader
[maxvertexcount(12)]
voidgeom(triangleGSPS_INPUTinput[3],inoutTriangleStreamoutStream)
{
GSPS_INPUToutput;
//Calculatethefacenormal
float3faceEdgeA=input[1].Pos-input[0].Pos;
float3faceEdgeB=input[2].Pos-input[0].Pos;
float3faceNormal=normalize(cross(faceEdgeA,faceEdgeB));
float3ExplodeAmt=faceNormal*_Explode;
//Calculatethefacecenter
float3centerPos=(input[0].Pos.xyz+input[1].Pos.xyz+input[2].Pos.xyz)/3.0;
float2centerTex=(input[0].Tex+input[1].Tex+input[2].Tex)/3.0;
centerPos+=faceNormal*_Explode;
//Outputthepyramid
for(inti=0;i<3;i++)
{
output.Pos=input[i].Pos+float4(ExplodeAmt,0);
output.Pos=mul(UNITY_MATRIX_MVP,output.Pos);
output.Norm=input[i].Norm;
output.Tex=input[i].Tex;
outStream.Append(output);
intiNext=(i+1)%3;
output.Pos=input[iNext].Pos+float4(ExplodeAmt,0);
output.Pos=mul(UNITY_MATRIX_MVP,output.Pos);
output.Norm=input[iNext].Norm;
output.Tex=input[iNext].Tex;
outStream.Append(output);
output.Pos=float4(centerPos,1)+float4(ExplodeAmt,0);
output.Pos=mul(UNITY_MATRIX_MVP,output.Pos);
output.Norm=faceNormal;
output.Tex=centerTex;
outStream.Append(output);
outStream.RestartStrip();
}
for(inti=2;i>=0;i--)
{
output.Pos=input[i].Pos+float4(ExplodeAmt,0);
output.Pos=mul(UNITY_MATRIX_MVP,output.Pos);
output.Norm=-input[i].Norm;
output.Tex=input[i].Tex;
outStream.Append(output);
}
outStream.RestartStrip();
}
//FRAG
fixed4frag(GSPS_INPUTi):COLOR0
{
fixed4col=tex2D(_MainTex,i.Tex);
returncol;
}
ENDCG
}
}
FallbackOff
}