正文
Geometry Shader 实现 Wireframe 绘制边线的Shader
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最终效果:
参考了一个免费插件
https://assetstore.unity.com/packages/vfx/shaders/directx-11/ucla-wireframe-shader-21897
基础思路======================================
在几何阶段计算每个顶点到第三边的距离,在片元中就可以插值得到每个点到顶点的距离
根据最小的距离只计算是否需要显示,结果就是只绘制边线
基础知识======================================
Geometry 在 Vertex 和 Fragment 之间 可选步骤
根据Vertex传入的顶点参数做一些调整,生成改动后的顶点结构,再调用Fragment着色器
//声明使用的几何着色器函数,类似声明 vertex 和 fragment
#pragma geometry geom
//限制GS输出的最大顶点数
[maxvertexcount(3)]
//第一个时入参 第二个是调整以后的数据
void geom(triangle v2g p[3], inout TriangleStream<g2f> triStream)
{
UCLAGL_geom( p, triStream);
}
入参格式 像fragment类似,传入的是vertex的计算结果 例如
struct v2g
{
float4 pos : POSITION; // vertex position
float2 uv : TEXCOORD0; // vertex uv coordinate
};
不一样的是一次可以处理多个结果
point v2g p[1]
line v2g p[2]
triangle v2g p[3]
返回参数 inout 必须
可以返回3中数据流 PointStream, LineStream, TriangleStream
流中的具体数据类似f2v的数据格式
struct g2f
{
float4 pos : POSITION; // fragment position
float2 uv : TEXCOORD0; // fragment uv coordinate
float3 dist : TEXCOORD1; // distance to each edge of the triangle
};
也是可以返回多个的
inout PointStream<g2f> poiStream
inout LineStream<g2f> linStream
inout PointStream<g2f> poiStream
inout LineStream<g2f> linStream
inout TriangleStream<g2f> triStream
Shader==================================================
Shader "Unlit/WithWireframeShder"
{
Properties
{
_MainColor ("Main Color", Color) = (1,1,1,1)
_LineColor ("Line Color", Color) = (0,0,0,1)
_Thickness ("Thickness", Float) = 1
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 100
//绘制基础颜色
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
float4 _MainColor;
struct appdata
{
float4 vertex : POSITION;
};
struct v2f
{
float4 pos : SV_POSITION;
};
v2f vert (appdata v)
{
v2f o;
o.pos = UnityObjectToClipPos(v.vertex);
return o;
}
fixed4 frag (v2f i) : SV_Target
{
return _MainColor;
}
ENDCG
}
//绘制线框
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma geometry geom
#pragma fragment frag
#include "UnityCG.cginc"
float4 _LineColor;
float _Thickness;
struct appdata
{
float4 vertex : POSITION;
};
struct v2g
{
float4 pos : SV_POSITION;
};
struct g2f
{
float4 pos : POSITION; // fragment position
float3 dist : TEXCOORD1; // distance to each edge of the triangle
};
v2g vert (appdata v)
{
v2g o;
o.pos = UnityObjectToClipPos(v.vertex);
return o;
}
[maxvertexcount(3)]
void geom(triangle v2g p[3], inout TriangleStream<g2f> triStream)
{
//points in screen space
float2 p0 = _ScreenParams.xy * p[0].pos.xy / p[0].pos.w;
float2 p1 = _ScreenParams.xy * p[1].pos.xy / p[1].pos.w;
float2 p2 = _ScreenParams.xy * p[2].pos.xy / p[2].pos.w;
//edge vectors
float2 v0 = p2 - p1;
float2 v1 = p2 - p0;
float2 v2 = p1 - p0;
//area of the triangle
float area = abs(v1.x*v2.y - v1.y * v2.x);
//values based on distance to the edges
float dist0 = area / length(v0);
float dist1 = area / length(v1);
float dist2 = area / length(v2);
g2f pIn;
//add the first point
pIn.pos = p[0].pos;
pIn.dist = float3(dist0,0,0);
triStream.Append(pIn);
//add the second point
pIn.pos = p[1].pos;
pIn.dist = float3(0,dist1,0);
triStream.Append(pIn);
//add the third point
pIn.pos = p[2].pos;
pIn.dist = float3(0,0,dist2);
triStream.Append(pIn);
}
fixed4 frag (g2f input) : SV_Target
{
//find the smallest distance
float val = min( input.dist.x, min( input.dist.y, input.dist.z));
//calculate power to 2 to thin the line
val = exp2( -1/_Thickness * val * val );
//丢弃不在边线上的
if (val < 0.5f) discard;
return _LineColor;
}
ENDCG
}
}
}
