Shader学习22——相交高亮扫描效果

实现方式和原理参考这篇

image.png
简单概况一下原理就是：获取当前顶点在屏幕的深度值z，如果跟场景中其他物体的深度z差距小于某个值则改变颜色。
最终效果：
Mar-29-2021 13-19-05.gif

代码如下：

Shader "Custom/相交高亮"
{
    Properties
    {
        _Color ("Main Tint", Color) = (1,1,1,1)
        _Threshold ("Threshold", Range(0, 1)) = 1
        _HighlightColor("HighlightColort", Color) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
        Pass {
            Tags { "LightMode"="ForwardBase" }
            Blend SrcAlpha OneMinusSrcAlpha 

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            
            fixed4 _Color;
            sampler2D _CameraDepthTexture;
            fixed _Threshold;
            fixed4 _HighlightColor;

            struct a2v{
                float4 vertex : POSITION; 
            };

            struct v2f{
                float4 pos : SV_POSITION;
                float4 projPos : TEXCOORD0; 
            };

            v2f vert(a2v v){
                v2f o;
                o.pos = UnityObjectToClipPos ( v.vertex );

                //ComputeScreenPos传入Clip Space坐标pos, 最终输出xy在[0, 1]之间, z值为Camera Space深度的结果
                o.projPos = ComputeScreenPos ( o.pos );
                //计算eye space的深度值
                o.projPos.z = COMPUTE_EYEDEPTH(o.projPos.z);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target {
                //unity提供了内置的纹理_CameraDepthTexture存储的是屏幕深度信息
                float sceneZ = LinearEyeDepth (tex2Dproj(_CameraDepthTexture, UNITY_PROJ_COORD(i.projPos)));
                float partZ = i.projPos.z;
                //如果两个顶点之间的Z值差小于_Threshold，则lerp颜色
                float diff = min ( (abs(sceneZ - partZ)) / _Threshold, 1);
                float4 finalColor = lerp(_HighlightColor, _Color, diff);
                return finalColor;
            }       
            ENDCG
        }
    }
    FallBack "Transparent/VertexLit"
}