【Shader】屏幕后处理-利用卷积算子计算边缘检测

Shader "Edge Detection" {
Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_EdgeOnly ("Edge Only", Float) = 1.0
_EdgeColor ("Edge Color", Color) = (0, 0, 0, 1)
_BackgroundColor ("Background Color", Color) = (1, 1, 1, 1)
}
SubShader {
Pass {
ZTest Always
Cull Off
ZWrite Off

CGPROGRAM

#include "UnityCG.cginc"

#pragma vertex vert
#pragma fragment fragSobel

sampler2D _MainTex;
uniform half4 _MainTex_TexelSize;
fixed _EdgeOnly;
fixed4 _EdgeColor;
fixed4 _BackgroundColor;

struct v2f {
float4 pos : SV_POSITION;
half2 uv[9] : TEXCOORD0;
};

v2f vert(appdata_img v) {
v2f o;
// 顶点投影坐标
o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
// uv坐标
half2 uv = v.texcoord;

// 纹素值*Sobel算子
o.uv[0] = uv + _MainTex_TexelSize.xy * half2(-1, -1);
o.uv[1] = uv + _MainTex_TexelSize.xy * half2(0, -2);
o.uv[2] = uv + _MainTex_TexelSize.xy * half2(1, -1);
o.uv[3] = uv + _MainTex_TexelSize.xy * half2(-2, 0);
o.uv[4] = uv + _MainTex_TexelSize.xy * half2(0, 0);
o.uv[5] = uv + _MainTex_TexelSize.xy * half2(2, 0);
o.uv[6] = uv + _MainTex_TexelSize.xy * half2(-1, 1);
o.uv[7] = uv + _MainTex_TexelSize.xy * half2(0, 1);
o.uv[8] = uv + _MainTex_TexelSize.xy * half2(1, 1);

return o;
}

// 固定参数，求亮度
fixed luminance(fixed4 color) {
return  0.2125 * color.r + 0.7154 * color.g + 0.0721 * color.b;
}

half Sobel(v2f i) {
const half Gy[9] = {-1,  0,  1,
-2,  0,  2,
-1,  0,  1};

const half Gx[9] = {-1, -2, -1,
0,  0,  0,
1,  2,  1};

half texColor;
half edgeX = 0;
half edgeY = 0;
for (int it = 0; it < 9; it++) {
texColor = luminance(tex2D(_MainTex, i.uv[it]));
edgeX += texColor * Gx[it];
edgeY += texColor * Gy[it];
}

half edge = 1 - abs(edgeX) - abs(edgeY);

return edge;
}

fixed4 fragSobel(v2f i) : SV_Target {
// edge值越小，表示越可能是边缘点
half edge = Sobel(i);

// i.uv[4]是0，0偏移，等同于UV坐标
// 边缘+彩色
fixed4 withEdgeColor = lerp(_EdgeColor, tex2D(_MainTex, i.uv[4]), edge);

// 边缘
fixed4 onlyEdgeColor = lerp(_EdgeColor, _BackgroundColor, edge);

// 边缘彩色混合
return lerp(withEdgeColor, onlyEdgeColor, _EdgeOnly);
}

ENDCG
}
}
FallBack Off
}