【OpenGL】Shader技巧集合

这篇文章将收集unity中使用shader的相关技巧和特效，会不断地更新内容。关于在Unity中使用shader的介绍，请参考《【OpenGL】使用Unity来学习OpenGL》 常用的内置uniform iResolution ＝》_ScreenParams iGlobalTime = _Time.y glFragCoord = f loat4 sp:WPOS

这篇文章将收集unity中使用shader的相关技巧和特效，会不断地更新内容。关于在Unity中使用shader的介绍，请参考《【OpenGL】使用Unity来学习OpenGL》

常用的内置uniform

iResolution ＝》_ScreenParams

iGlobalTime => _Time.y

glFragCoord => float4 sp:WPOS  // 需要 #pragma target 3.0， 另外的方式请见下面

vec2 => float2

mix => lerp

mod => fmod

texture2D => tex2D

textureCube => texCUBE

mat2=>float2x2

fract=>frac

========

关于glFragCoord， 可以使用另外一种方式计算（支持3.0之前的）参考官方例子

o.scrPos = ComputeScreenPos(o.pos);

float2 wcoord = (i.scrPos.xy/i.scrPos.w);

-------

float2 wcoord = sp.xy/_ScreenParams.xy;

关于数学的Shader：https://www.shadertoy.com/view/ldlSD2    https://www.shadertoy.com/view/ldlSWj

很好的一个教程：http://ogldev.atspace.co.uk/index.html

Deferred Shading 原理: http://ogldev.atspace.co.uk/www/tutorial35/tutorial35.html 

关于Stencil Buffer 的理解：http://www.cnblogs.com/mikewolf2002/archive/2012/05/15/2500867.html

更多文章：1）http://docs.unity3d.com/Manual/SL-Stencil.html

2) http://answers.unity3d.com/questions/590800/how-to-cullrender-to-through-a-window.html

Stencil Shadow Volume : http://ogldev.atspace.co.uk/www/tutorial40/tutorial40.html

http://en.wikipedia.org/wiki/Shadow_volume

镜面反射的实现原理：

ftp://ftp.sgi.com/sgi/opengl/contrib/blythe/advanced99/notes/node158.html

其它镜面反射：

http://en.wikibooks.org/wiki/Cg_Programming/Unity/Mirrors

在unity cg中可以使用[HideInInspector]来隐藏uniform属性，这样就可以用作自定义常量。

Physically Based Rendering:   Tutorial: Physically Based Rendering, And you can too!

边缘检测：1) http://www.codeproject.com/Articles/94817/Pixel-Shader-for-Edge-Detection-and-Cartoon-Effect

2) http://coding-experiments.blogspot.hk/2010/06/edge-detection.html

3) http://en.wikipedia.org/wiki/Edge_detection

Cg函数表：http://http.developer.nvidia.com/CgTutorial/cg_tutorial_appendix_e.html

heat effect : http://forum.unity3d.com/threads/50132-Heat-Distortion,   http://www.cnblogs.com/geoffyange/archive/2013/06/06/3122570.html

skin shading in unity: http://www.altdevblogaday.com/2011/12/31/skin-shading-in-unity3d/

http://http.developer.nvidia.com/GPUGems3/gpugems3_ch14.html

http://gamedev.stackexchange.com/questions/31308/algorithm-for-creating-spheres

RenderMan University: http://renderman.pixar.com/view/renderman-university

一些shader的例子：

Shader "stalendp/shaderTest02" { //see https://www.shadertoy.com/view/4sj3zy
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 3.0
			
			#include "UnityCG.cginc"

			sampler2D _MainTex;
		
			//Variable declarations
			
			struct myvars {
				float3 bgColor;
				float sphereScale;
				float sphereShine;
				float3 sphereDiff;
				float3 sphereSpec;
				float2 specPoint;
			};

			float4 vert(appdata_base v) : POSITION {
				return mul(UNITY_MATRIX_MVP, v.vertex);
			}
			
			float4 frag(float4 sp:WPOS): COLOR {
				myvars mv;
				mv.bgColor = float3(0.6, 0.5, 0.6);
				mv.sphereScale = 0.7;
				mv.sphereShine = 0.5;
				mv.sphereDiff = float3(0.5, 0.0, 0.5);
				mv.sphereSpec = float3(1.0, 1.0, 1.0);
				mv.specPoint = float2(0.2, -0.1);
			
				// creates shader pixel coordinates
				float2 uv = sp.xy/_ScreenParams.xy;
				// sets the position of the camera
				float2 p = uv * 2.5 - float2(1.0, 1.0);
				p.x *= _ScreenParams.x / _ScreenParams.y;
				
				// Rotates the sphere in a circle
				p.x += cos(-_Time.y) *0.35;
				p.y += sin(-_Time.y) * 0.35;
				
				// Rotates the specular point with the sphere
				mv.specPoint.x += cos(-_Time.y) * 0.35;
				mv.specPoint.y += sin(-_Time.y) * 0.35;
				
				//Sets the radius of the sphere to the middle of the screen
				float radius = length(p);//sqrt(dot(p, p));
	
				float3 col = mv.bgColor;
	
				//Sets the initial dark shadow around the edge of the sphere
				float f = smoothstep(mv.sphereScale * 0.7, mv.sphereScale, length(p + mv.specPoint));
				col -= lerp(col, float3(0.0,0.0,0.0), f) * 0.2;
				
				//Only carries out the logic if the radius of the sphere is less than the scale
				if(radius <br>
<br>


<pre class="brush:php;toolbar:false">Shader "Custom/shaderTest03" {  // https://www.shadertoy.com/view/Xdf3DS
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
	
		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 3.0
			
			#include "UnityCG.cginc"

			sampler2D _MainTex;

			
			struct myvars {
				float k;
				float f;
				float threshold;

				float3 colour;
				float3 normal;

				float3 lightPos;
				float3 lightColour;
				float3 ambient;
				float shinyness;
				float diffuseFactor;
				float4 fragCoord;
			};
			

			float2 center ( float2 border , float2 _offset , float2 vel, myvars mv) {
				float2 c = _offset + vel * _Time * 0.5;
				c = fmod ( c , 2. - 4. * border );
				if ( c.x > 1. - border.x ) c.x = 2. - c.x - 2. * border.x;
				if ( c.x  1. - border.y ) c.y = 2. - c.y - 2. * border.y;
				if ( c.y  b )
					return 0.0;
				if ( r >= b/3.0 ) {
					float rb = 1.0 - r/b;
					return (3.0*mv.k)/2.0 * rb * rb;
				}
				if ( r >= 0.0 && r <br>
<pre class="brush:php;toolbar:false">Shader "stalendp/shaderTest04" { //see https://www.shadertoy.com/view/Xsf3R8
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 3.0
			
			#include "UnityCG.cginc"

			sampler2D _MainTex;
			
			struct Ray {
				float3 org;
				float3 dir;
			};
			
			float rayPlaneIntersect( Ray ray, float4 plane ) {
				float f = dot( ray.dir, plane.xyz );
				
				float t = -( dot( ray.org, plane.xyz ) + plane.w );
				t /= f;
				
				return t;
			}
			
			float3 shade( float3 pos, float3 nrm, float4 light ) {
				float3 toLight = light.xyz - pos;
				float toLightLen = length( toLight );
				toLight = normalize( toLight );
					
				float diff = dot( nrm, toLight );
				float attn = 1.0 - pow( min( 1.0, toLightLen / light.w ), 2.0 );
				float comb = 2.0 * diff * attn;
				
				return float3( comb, comb, comb );
			}


			float4 vert(appdata_base v) : POSITION {
				return mul(UNITY_MATRIX_MVP, v.vertex);
			}
			
			float4 frag(float4 sp:WPOS): COLOR {
			
				// gl_FragCoord: location (0.5, 0.5) is returned 
				// for the lower-left-most pixel in a window
				
				// XY of the normalized device coordinate
				// ranged from [-1, 1]
				float2 ndcXY = -1.0 + 2.0 * sp.xy / _ScreenParams.xy;
				
				// aspect ratio
				float aspectRatio = _ScreenParams.x / _ScreenParams.y;
				
				// scaled XY which fits the aspect ratio
				float2 scaledXY = ndcXY * float2( aspectRatio, 1.0 );
				
				// camera XYZ in world space
				float3 camWsXYZ = float3( 0.0, 1.0, 0.0 );
				camWsXYZ.z += 10.0 * cos( _Time.y );
				
				// construct the ray in world space
				Ray ray;
				ray.org = camWsXYZ;
				ray.dir = float3( scaledXY, -2.0 ); // OpenGL is right handed
				
				// define the plane in world space
				float4 plane = float4( 0.0, 1.0, 0.0, 0.0 );
				
				float t = rayPlaneIntersect( ray, plane );
				
				// define the point light in world space (XYZ, range)
				float4 lightWs = float4( 0.0, 5.0, -5.0, 10.0 );
				
				if ( t >= 0.0 )
				{
					float3 sceneWsPos = ray.org + t * ray.dir;
					float3 sceneWsNrm = plane.xyz;
					float2 sceneUV = sceneWsPos.xz / 4.0;
					
					float4 sceneBase = tex2D( _MainTex, sceneUV );		
					float3 sceneShade = shade( sceneWsPos, sceneWsNrm, lightWs );
					
					return float4( sceneShade * sceneBase.xyz, 1.0 );
				}
			
				return float4( 0.0, 0.0, 0.0, 1.0 );
			}
			
			ENDCG
		}
	} 
	FallBack "Diffuse"
}

Shader "stalendp/shaderTest04" { //see https://www.shadertoy.com/view/MdB3Dw
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 3.0
			
			#include "UnityCG.cginc"
			
			#define USE_ANALYTICAL_MBLUR

			sampler2D _MainTex;
	
			// intersect a MOVING sphere
			float2 iSphere( in float3 ro, in float3 rd, in float4 sp, in float3 ve, out float3 nor )
			{
			    float t = -1.0;
				float s = 0.0;
				nor = float3(0.0);
				
				float3  rc = ro - sp.xyz;
				float A = dot(rc,rd);
				float B = dot(rc,rc) - sp.w*sp.w;
				float C = dot(ve,ve);
				float D = dot(rc,ve);
				float E = dot(rd,ve);
				float aab = A*A - B;
				float eec = E*E - C;
				float aed = A*E - D;
				float k = aed*aed - eec*aab;
					
				if( k>0.0 )
				{
					k = sqrt(k);
					float hb = (aed - k)/eec;
					float ha = (aed + k)/eec;
					
					float ta = max( 0.0, ha );
					float tb = min( 1.0, hb );
					
					if( ta 0.0 )
				{
					t = -b - sqrt(k);
					nor = normalize( (ro+rd*t) - sp.xyz );
				}

				return t;
			}

			float3 getPosition( float time ) { return float3(     2.5*sin(8.0*time), 0.0,      1.0*cos(8.0*time) ); }
			float3 getVelocity( float time ) { return float3( 8.0*2.5*cos(8.0*time), 0.0, -8.0*1.0*sin(8.0*time) ); }


			float4 vert(appdata_base v) : POSITION {
				return mul(UNITY_MATRIX_MVP, v.vertex);
			}
			
			float4 frag(float4 sp:WPOS): COLOR {
				float2 q = sp.xy / _ScreenParams.xy;
				float2 p = -1.0 + 2.0*q;
				p.x *= _ScreenParams.x/_ScreenParams.y;	

				// camera
				float3  ro = float3(0.0,0.0,4.0);
			    float3  rd = normalize( float3(p.xy,-2.0) );
				
			    // sphere	
				
				// render
				float3  col = float3(0.0);
				
				#ifdef USE_ANALYTICAL_MBLUR
							
			    //---------------------------------------------------	
			    // render with analytical motion blur
			    //---------------------------------------------------	
				float3  ce = getPosition( _Time.y );
				float3  ve = getVelocity( _Time.y );
			    	
				col = float3(0.25) + 0.3*rd.y;
				float3 nor = float3(0.0);
				float3 tot = float3(0.25) + 0.3*rd.y;
			    float2 res = iSphere( ro, rd, float4(ce,1.0), ve/24.0, nor );
				float t = res.x;
				if( t>0.0 )
				{
					float dif = clamp( dot(nor,float3(0.5703)), 0.0, 1.0 );
					float amb = 0.5 + 0.5*nor.y;
					float3  lcol = dif*float3(1.0,0.9,0.3) + amb*float3(0.1,0.2,0.3);
					col = lerp( tot, lcol, res.y );
				}
				
				#else
				
			    //---------------------------------------------------	
			    // render with brute force sampled motion blur
			    //---------------------------------------------------	
				
			    #define NUMSAMPLES 32
				float3 tot = float3(0.0);
				for( int i=0; i<numsamples i float fi="float(i)/float(NUMSAMPLES);" float3 ce="getPosition(" _time.y nor="float3(0.0);" tmp="float3(0.25)" t="iSphere(" ro rd float4 if>0.0 )
			        {
			            float dif = clamp( dot(nor,float3(0.5703)), 0.0, 1.0 );
			            float amb = 0.5 + 0.5*nor.y;
			            tmp = dif*float3(1.0,0.9,0.3) + amb*float3(0.1,0.2,0.3);
			        }
			        col += tmp;
				}		
				col /= float(NUMSAMPLES);
					
			    #endif
				
				col = pow( clamp(col,0.0,1.0), float3(0.45) );

				return float4( col, 1.0 );
			}
			
			ENDCG
		}
	} 
	FallBack "Diffuse"
}
</numsamples>

Shader "stalendp/shaderTest05" { //see https://www.shadertoy.com/view/XsB3DW
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		_CubeDiffuse ("Cubemap Diffuse Map", CUBE) = "" {}
		vv1("vv1", float) = -1.0
		vv2("vv2", float) = 2.0
	}
	SubShader {
		Pass {
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 3.0
			//下面防止编译错误：instruction limit of 1024 exceed;
			#pragma glsl  
			
			#include "UnityCG.cginc" 
			
			#define MAX_STEPS 64
			#define MAX_REFLECTIONS 4
			#define PI 3.1415926536

			sampler2D _MainTex;
			samplerCUBE _CubeDiffuse;
			float vv1, vv2;
	
			struct Ray {
				float3 o;
				float3 d;
			};
			struct Sphere {
				float3 o;
				float r;
			};
			struct Box {
				float3 o;
				float3 s;
			};
			struct Torus {
				float3 o;
				float2 s;
			};
						
			float2 rotate2d(in float2 v, in float a) {
				float sinA = sin(a);
				float cosA = cos(a);
				return float2(v.x * cosA - v.y * sinA, v.y * cosA + v.x * sinA);	
			}

			float sdSphere(in float3 p, in Sphere s) {
				return length(p-s.o)-s.r;
			}
			float sdBox(in float3 p, in Box b) {
				float3 d = abs(p-b.o) - b.s;
				return min(max(d.x,max(d.y,d.z)),0.0) +
					length(max(d,0.0));
			}
			float sdTorus(in float3 p, in Torus t) {
				p -= t.o;
				float2 q = float2(length(p.xz)-t.s.x,p.y);
				return length(q)-t.s.y;
			}
			float world(in float3 p) {
				float ti = fmod(_Time.y,10.);
				if(ti > 2.) {
					Sphere s0 = Sphere(float3(0),1.);
					Box b0 = Box(float3(0),float3(.8));
					if(ti <br>
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