【OpenGL】Shader实例分析（十）- 钻石效果

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好久没有写文章了，赶紧补几篇。最近研究了一个玻璃折射的效果（用在钻石上），虽然没有达到最满意的效果，还是先分享出来，待以后有更好的想法再补充。

先看效果吧：

这里面有两个效果，左边是unity的免费插件Gem Shader，右边的是我自己实现的，我将分别介绍这两个效果的实现方法。

一、知识补充：

钻石的图片：

两个shader都使用了CubeMap...

Shader "FX/Diamond"{Properties {_Color ("Color", Color) = (1,1,1,1)_ReflectTex ("Reflection Texture", Cube) = "dummy.jpg" {TexGen CubeReflect}_RefractTex ("Refraction Texture", Cube) = "dummy.jpg" {TexGen CubeReflect}}SubShader {Tags {"Queue" = "Transparent"}// First pass - here we render the backfaces of the diamonds. Since those diamonds are more-or-less// convex objects, this is effectively rendering the inside of themPass {Color (0,0,0,0)Offset  -1, -1Cull FrontZWrite OffSetTexture [_RefractTex] {constantColor [_Color]combine texture * constant, primary}SetTexture [_ReflectTex] {combine previous, previous +- texture}}// Second pass - here we render the front faces of the diamonds.Pass {Fog { Color (0,0,0,0)}ZWrite onBlend One OneSetTexture [_RefractTex] {constantColor [_Color]combine texture * constant}SetTexture [_ReflectTex] {combine texture + previous, previous +- texture}}}// Older cards. Here we remove the bright specular highlightSubShader {// First pass - here we render the backfaces of the diamonds. Since those diamonds are more-or-less// convex objects, this is effectively rendering the inside of themPass {Color (0,0,0,0)Cull FrontSetTexture [_RefractTex] {constantColor [_Color]combine texture * constant, primary}}// Second pass - here we render the front faces of the diamonds.Pass {Fog { Color (0,0,0,0)}ZWrite offBlend One OneSetTexture [_RefractTex] {constantColor [_Color]combine texture * constant}}}// Ancient cards without cubemapping support// We could use a 2D refletction texture, but the chances of getting one of these cards are slim, so we won't bother.SubShader {Pass {Color [_Color]}}}

Shader "stalendp/myDiamondShader" {Properties {_Color ("Color", Color) = (1,1,1,1)_ReflectTex ("Reflection Texture", Cube) = "" { }_RefractTex ("Refraction Texture", Cube) = "" { }}CGINCLUDE          #include "UnityCG.cginc"                             fixed4 _Color;          samplerCUBE _RefractTex;            samplerCUBE _ReflectTex;                       struct v2f {                  half4 pos:SV_POSITION;                  half3 Reflect : TEXCOORD0;             half3 RefractR : TEXCOORD1;        half3 RefractG : TEXCOORD2;        half3 RefractB : TEXCOORD3;        half Ratio : TEXCOORD4;        };                v2f vert(appdata_full v) {    float EtaR = 0.65;float EtaG = 0.67;float EtaB = 0.69;float FresnelPower = 5.0;float F = ((1.0-EtaG) * (1.0-EtaG)) / ((1.0+EtaG) * (1.0+EtaG));float3 i = -normalize(ObjSpaceViewDir(v.vertex)); float3 n = normalize(v.normal); // ??????v2f o;o.Ratio = F + (1.0 - F) * pow((1.0 - dot(-i, n)), FresnelPower) ;o.RefractR = refract(i, n, EtaR);o.RefractG = refract(i, n, EtaG);o.RefractB = refract(i, n, EtaB);o.Reflect = reflect(i, n);o.pos = mul (UNITY_MATRIX_MVP, v.vertex);                   return o;            }                fixed4 frag(v2f i) : COLOR0 {          float3 refractColor, reflectColor;                refractColor.r = float3(texCUBE(_RefractTex, i.RefractR)).r;        refractColor.g = float3(texCUBE(_RefractTex, i.RefractG)).g;        refractColor.b = float3(texCUBE(_RefractTex, i.RefractB)).b;        reflectColor = float3(texCUBE(_ReflectTex, i.Reflect));                   return  2*_Color * pow(fixed4(lerp( _Color * refractColor * 5, reflectColor * 2, i.Ratio), 1), 1.8);        }        ENDCG              SubShader {             Pass {                  CGPROGRAM                  #pragma vertex vert                  #pragma fragment frag                  #pragma fragmentoption ARB_precision_hint_fastest                       ENDCG              }      }      FallBack Off    }

关键词： diamond、crystal、glass、refraction、cubeMap、钻石、水晶、玻璃、折射
参考资料：

1. CubeMap技术相关：http://docs.unity3d.com/Manual/SL-ImplementingTexGen.html

2.［GPU Gems］Environment Mapping Techniques：http://http.developer.nvidia.com/CgTutorial/cg_tutorial_chapter07.html

3.《OpenGL Shading Language 3rd edition》14.1 Refraction ： https://www.scss.tcd.ie/Michael.Manzke/CS7055/GLSL/GLSL-3rdEd-refraction.pdf

4.［GPU Gems］Generic Refraction Simulation：http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter19.html

5. 某个大学的ppt：http://users.ece.gatech.edu/lanterma/mpg08/mpglecture13f08_4up.pdf

6. Fresnel原理：http://www.3drender.com/glossary/fresneleffect.htm

7. AMD关于diamond算法的文章：http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/Gosselin_Gem.pdf

8. CG Shaders - Cubemap Refraction： http://www.artisticexperiments.com/cg-shaders/cg-shaders-cubemap-refraction

9. 水滴折射效果：http://wiki.unity3d.com/index.php?title=RefractionEffect

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