Shader教程：屏幕后处理-利用卷积算子计算边缘检测
发表于2018-03-29
卷积操作是使用一个卷积核(kernel)对一张图像中的每个像素进行一系列的操作，再通过简单计算过程可以实现图像处理效果中的边缘检测了。那下面就和大家介绍下利用卷积算子计算边缘检测的代码实现。
代码如下：
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)
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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;
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// 固定参数，求亮度
fixed luminance(fixed4 color) ｛
return 0.2125 * color.r + 0.7154 * color.g + 0.0721 * color.b;
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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];
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half edge = 1 - abs(edgeX) - abs(edgeY);
return edge;
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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);
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ENDCG
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FallBack Off
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