unity绘制虚线 geometry shader

Posted 2023-03-30

参考技术A 绘制虚线其实简单。绘制线段，然后通过线段的uv坐标，设置虚线贴图就行。

或者用shader判断uv坐标决定好不要绘制线段的某一部分。

但是这样还是免不了要在CPU中计算好顶点和UV。如果线条数量很多（曲线），要经常更新线条。而且要修改条线的粗细，虚线的密度。那么为什么不把要显示的东西交给GPU呢？

CPU端直接用两个点就好了，也减少了CPU的计算量和额外的数据存储。

绘制线条的抗锯齿效果比绘制三角形抗锯齿效果要差一些

Shader "Unlit/geoline"



    Properties

   

        _MainTex ("Texture", 2D) = "white"

        _LineColor("LineColor", color) = (0,1,0,1)//颜色

        _LineWidth("LineWidth",float) = 10//线宽

        _SingleSegmentLength("SingleSegmentLength",float) = 500//线段单元长度

        _SolidRatio("SolidRatio",float) = 0.5//绘制实线部分比率

   

    SubShader

   

        Cull Off

        Blend SrcAlpha OneMinusSrcAlpha

        Tags "Queue"="Transparent"

        LOD 100

        Pass

       

            CGPROGRAM

            #pragma vertex vert

            #pragma geometry geo//几何着色器入口

            #pragma fragment frag

            // make fog work

            //#pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata

           

                float4 vertex : POSITION;

                float2 uv : TEXCOORD0;

            ;

            struct v2f

           

                float2 uv : TEXCOORD0;

                //UNITY_FOG_COORDS(1)

                float4 vertex : SV_POSITION;

            ;

            sampler2D _MainTex;

            float4 _MainTex_ST;

            float _LineWidth;

            float _SingleSegmentLength;

            float _SolidRatio;

            float4 _LineColor;

            [maxvertexcount(30)]//产生最大的顶点数，append到triStream的次数应该小于此。最大好像是64

            void geo(line appdata l[2], inout TriangleStream<v2f> triStream)

            

                v2f pIn;

                v2f v[4];//先生成四个点，构造两个三角形

                float4 a = l[0].vertex;

                float4 b = l[1].vertex;

                float len = distance(b, a);

                float3 dir0 = normalize(b - a);

                float3 dir2 = normalize(cross(dir0, float3(0, 0, 1)));//加宽的方向

                float2 dir3 = dir2.xy * 0.5 * _LineWidth;

                v[0].vertex = UnityObjectToClipPos(a + float4(dir3, 0, 0));

                //使用的原来的世界坐标空间计算，完了后再映射为视图空间。如果是在顶点着色进行UnityObjectToClipPos后，坐标空间就是屏幕坐标了。

                //屏幕坐标经过投影变换。如果在vertex shader 计算UnityObjectToClipPos。a, b点的坐标x,y,z就不是均匀。垂直于线段的向量dir2就不对。

                v[0].uv = float2(0.0f, 1.0f) * float2(len / _SingleSegmentLength, 1.0f);

                v[1].vertex = UnityObjectToClipPos(b + float4(dir3, 0, 0));

                v[1].uv = float2(1.0f, 1.0f) * float2(len / _SingleSegmentLength, 1.0f);

                v[2].vertex = UnityObjectToClipPos(b + float4(-dir3, 0, 0));

                v[2].uv = float2(1.0f, 0.0f) * float2(len / _SingleSegmentLength, 1.0f);

                v[3].vertex = UnityObjectToClipPos(a + float4(-dir3, 0, 0));

                v[3].uv = float2(0.0f, 0.0f) * float2(len / _SingleSegmentLength, 1.0f);

                triStream.Append(v[0]);

                triStream.Append(v[1]);

                triStream.Append(v[2]);

                triStream.RestartStrip();//重置三角形计数，提交三角形

                triStream.Append(v[2]);

                triStream.Append(v[3]);

                triStream.Append(v[0]);

                triStream.RestartStrip();

                //最后倒下角，美化一下。这里可选。

                v2f va[3];

                v2f vb[3];

                float pi = 3.1415926;

                float points = 3;

                float segs = points + 1;

                for (int i = 1;i <= points;i++)

                

                    float2 rot = normalize(-dir0 * sin(i / segs * pi) + dir2 * cos(i / segs * pi));

                    va[i - 1].vertex = UnityObjectToClipPos(a + float4(rot * 0.5 * _LineWidth, 0, 0));

                    va[i - 1].uv = float2(0, dot(rot, dir2)) * float2(len / _SingleSegmentLength, 1.0f);

                

                for (int i = 1;i <= points;i++)

                

                    float2 rot = normalize(dir0 * sin(i / segs * pi) + -dir2 * cos(i / segs * pi));

                    vb[i - 1].vertex = UnityObjectToClipPos(b + float4(rot * 0.5 * _LineWidth, 0, 0));

                    vb[i - 1].uv = float2(1, dot(rot, dir2)) * float2(len / _SingleSegmentLength, 1.0f);

                

                for (int i = 0;i < points;i++)

                

                    triStream.Append(v[3]);

                    triStream.Append(va[i]);

                    if (i - 1 < 0)

                        triStream.Append(v[0]);

                    else

                        triStream.Append(va[i - 1]);

                    triStream.RestartStrip();

                    triStream.Append(v[1]);

                    triStream.Append(vb[i]);

                    if (i - 1 < 0)

                        triStream.Append(v[2]);

                    else

                        triStream.Append(vb[i - 1]);

                    triStream.RestartStrip();

                

           

            v2f vert (appdata v)

           

                v2f o;

                o.vertex = v.vertex;

                //o.vertex = UnityObjectToClipPos(v.vertex);

                //o.uv = TRANSFORM_TEX(v.uv, _MainTex);

                //UNITY_TRANSFER_FOG(o,o.vertex);

                return o;

           

            fixed4 frag (v2f i) : SV_Target

           

                // sample the texture

                //fixed4 col = tex2D(_MainTex, i.uv);

                fixed4 col = float4(0, 1, 0, 0);

                float m = fmod(i.uv.x, 1);

                if (m < _SolidRatio)

                

                    col = _LineColor;

                

                // apply fog

                //UNITY_APPLY_FOG(i.fogCoord, col);

                return col;

           

            ENDCG