【OpenGL】Shader实例分析（五）- 边缘检测

来源：互联网发布：国内餐饮软件排名编辑：程序博客网时间：2024/04/30 09:41

转发请保持地址：http://blog.csdn.net/stalendp/article/details/23139953

这里将介绍基于法线的边缘检测方法，这里的shader是参考官方的：http://wiki.unity3d.com/index.php/Outlined_Diffuse_3；运行效果如下：

代码如下：

Shader "Outlined/Diffuse" { // see http://wiki.unity3d.com/index.php/Outlined_Diffuse_3Properties {_Color ("Main Color", Color) = (.5,.5,.5,1)_OutlineColor ("Outline Color", Color) = (0,0,0,1)_Outline ("Outline width", Range (.002, 0.03)) = .005_MainTex ("Base (RGB)", 2D) = "white" { }} CGINCLUDE#include "UnityCG.cginc" struct appdata {float4 vertex : POSITION;float3 normal : NORMAL;}; struct v2f {float4 pos : POSITION;float4 color : COLOR;}; uniform float _Outline;uniform float4 _OutlineColor; v2f vert(appdata v) {// just make a copy of incoming vertex data but scaled according to normal directionv2f o;o.pos = mul(UNITY_MATRIX_MVP, v.vertex); float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);float2 offset = TransformViewToProjection(norm.xy);o.pos.xy += offset * o.pos.z * _Outline;// following please refer to : http://unitygems.com/noobs-guide-shaders-6-toon-shader/// o.pos = mul( UNITY_MATRIX_MVP, v.vertex + (float4(v.normal,0) * _Outline)); o.color = _OutlineColor;return o;}ENDCG SubShader {//Tags {"Queue" = "Geometry+100" }CGPROGRAM#pragma surface surf Lambert sampler2D _MainTex;fixed4 _Color; struct Input {float2 uv_MainTex;}; void surf (Input IN, inout SurfaceOutput o) {fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;o.Albedo = c.rgb;o.Alpha = c.a;}ENDCG // note that a vertex shader is specified here but its using the one abovePass {Name "OUTLINE"Tags { "LightMode" = "Always" }Cull FrontZWrite OnColorMask RGBBlend SrcAlpha OneMinusSrcAlpha//Offset 50,50 CGPROGRAM#pragma vertex vert#pragma fragment fraghalf4 frag(v2f i) :COLOR { return i.color; }ENDCG}} SubShader {CGPROGRAM#pragma surface surf Lambert sampler2D _MainTex;fixed4 _Color; struct Input {float2 uv_MainTex;}; void surf (Input IN, inout SurfaceOutput o) {fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;o.Albedo = c.rgb;o.Alpha = c.a;}ENDCG Pass {Name "OUTLINE"Tags { "LightMode" = "Always" }Cull FrontZWrite OnColorMask RGBBlend SrcAlpha OneMinusSrcAlpha CGPROGRAM#pragma vertex vert#pragma exclude_renderers gles xbox360 ps3ENDCGSetTexture [_MainTex] { combine primary }}} Fallback "Diffuse"}

原理介绍：

分两个pass进行渲染，第一个渲染边框，第二个渲染实物。

1）边框的渲染

在vertex Shader阶段，吧顶点按照法线的方向进行扩展，这样物体就比原来要膨胀（关于膨胀效果，请参考Surface Shader Example中的Normal Extrusion with Vertex Modifier）。

o.pos = mul(UNITY_MATRIX_MVP, v.vertex);float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);float2 offset = TransformViewToProjection(norm.xy);  //计算法线的方向o.pos.xy += offset * o.pos.z * _Outline; //按照法线的方向进行偏移

效果如下：

边框盖住里原始物体，这里只要设置只渲染背面，就可以达到效果，在渲染边框的Pass中设置“Cull Front”就可以了。

2）渲染实物

略

当然这个只是适用于3d物体，图像的边缘检测，还有canny算法等，以后再补充，这里给个Canny的地址：Canny Edge Detection Tutorial

另外一篇：http://en.wikipedia.org/wiki/Edge_detection; 还有： http://en.wikipedia.org/wiki/Canny_edge_detector

关于图像的边缘检测，可以运用在Deferred shading中的anti-aliasing中

======

相关的文章：http://unitygems.com/noobs-guide-shaders-6-toon-shader/

Silhouette-Outlined Diffuse

OutlinedDiffuse

Lighted Bumped Outline

基于法线的边缘检测

Code Snippet: Edge Detector/Antialiasing Shader

0 0