内置shader辅助函数定义在UnityCG.cginc文件中
顶点转换函数：
| Function: |
Description: |
| float4 UnityObjectToClipPos(float3 pos) |
Transforms a point from object space to the camera’s clip space in homogeneous coordinates. This is the equivalent of mul(UNITY_MATRIX_MVP, float4(pos, 1.0)), and should be used in its place. homogeneous coordinates：齐次坐标 等价于：mul(UNITY_MATRIX_MVP, float4(pos, 1.0)), |
| float3 UnityObjectToViewPos(float3 pos) |
Transforms a point from object space to view space. This is the equivalent of mul(UNITY_MATRIX_MV, float4(pos, 1.0)).xyz, and should be used in its place. 等价于：mul(UNITY_MATRIX_MV, float4(pos, 1.0)). |
Generic helper functions（定义在UnityCG.cginc文件中）
| Function: |
Description: |
| float3 WorldSpaceViewDir (float4 v) |
Returns world space direction (not normalized) from given object space vertex position towards the camera .(参数是object space下的顶点坐标，取得world space下指向摄像机的方向，即视角方向) |
| float3 ObjSpaceViewDir (float4 v) |
Returns object space direction (not normalized) from given object space vertex position towards the camera. （同上，不过取到的视角方向是在object space上的） |
| float2 ParallaxOffset (half h, half height, half3 viewDir) |
calculates UV offset for parallax normal mapping. 为视差法线贴图计算UV偏移 |
| fixed Luminance (fixed3 c) |
Converts color to luminance (grayscale). 将颜色转换为亮度（灰度） |
| fixed3 DecodeLightmap (fixed4 color) |
Decodes color from Unity lightmap (RGBM or dLDR depending on platform). 从烘焙贴图解码,烘焙贴图生成的是EXR格式的HDR贴图，根据不同平台返回RGBM或dLDR |
| float4 EncodeFloatRGBA (float v) |
Encodes [0..1) range float into RGBA color, for storage in low precision render target. 把float编码到RGBA8 |
| float DecodeFloatRGBA (float4 enc) |
Decodes RGBA color into a float.上面方法的反编 |
| float2 EncodeFloatRG (float v) |
Encodes [0..1) range float into a float2. 编码 [0.0,1.0)float--> float2 |
| float DecodeFloatRG(float2 enc) |
Decodes a previously-encoded RG float. float2解码--> [0.0,1.0) |
| float2 EncodeViewNormalStereo (float3 n) |
Encodes view space normal into two numbers in 0..1 range. 视空间法线(float3)编码到float2 |
| float3 DecodeViewNormalStereo (float4 enc4) |
Decodes view space normal from enc4.xy. 上面方法的解码,只使用参数的xy值 |
Forwardrendering helper functions in UnityCG.cginc
These functions are only useful when using forward rendering(ForwardBase or ForwardAdd pass types).
仅用于前向渲染
| Function: |
Description: |
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Computes world space direction (not normalized) to light, given object space vertex position. 参数是object space下的顶点坐标，取得world space下指向光源的方向 |
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Computes object space direction (not normalized) to light, given object space vertex position. 参数是object space下的顶点坐标，取得object space下指向光源的方向 |
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Computes illumination from four point lights, with light data tightly packed into vectors. Forward rendering uses this to compute per-vertex lighting. 正向渲染中，最多有4个点光源会以逐顶点渲染的方式被计算。 |
Vertex-lithelper functions in UnityCG.cginc
These functionsare only useful when using per-vertex lit shaders (“Vertex” pass type).
仅用于per-vertex lit shaders
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Description: |
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Computes illumination from four per-vertex lights and ambient, given object space position & normal. 参数为顶点跟法线，根据四个逐顶点光源跟环境光计算光照 |
mul（UNITY_MATRIX_MVP,v）跟ComputeScreenPos的区别
一个是model position->projection position 投影坐标
一个是projection position->screen position...屏幕坐标
投影坐标系->屏幕坐标系这是最简单的。2D坐标变换。也不多说。
使用例子：
o.position = mul(UNITY_MATRIX_MVP, v.vertex);
o.proj0 = ComputeScreenPos(o.position);
COMPUTE_EYEDEPTH(o.proj0.z);
有关深度的一些方法整理：
UNITY_TRANSFER_DEPTH(o):计算eye space的深度值，并写入变量o(float2)。
当需要渲染到一张深度贴图时，在vertex shader中使用该函数。
UNITY_OUTPUT_DEPTH(i): returns eye space depth from i (which must be a float2). Use it in a fragment programwhen rendering into a depth texture.
示例，制作深度贴图用：
Shader"Render Depth" {
SubShader{
Tags { "RenderType"="Opaque"}
Pass {
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include"UnityCG.cginc"
structv2f {
float4 pos : SV_POSITION;
float2 depth : TEXCOORD0;
}
v2fvert (appdata_base v) {
v2f o;
o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
UNITY_TRANSFER_DEPTH(o.depth);
return o;
}
half4frag(v2f i) : SV_Target {
UNITY_OUTPUT_DEPTH(i.depth);
}
ENDCG
}
}
}
COMPUTE_EYEDEPTH(o):computes eye spacedepth of the vertex and outputs it in o. Use it in a vertexprogram when not rendering into adepth texture
实现代码#define COMPUTE_EYEDEPTH(o) o =-mul( UNITY_MATRIX_MV, v.vertex ).z设置o为当前顶点视空间的z值，在vertex 函数中使用
DECODE_EYEDEPTH(i):given high precision value from depth texture i, returns corresponding eye space depth. This macro just returnsi*FarPlane on Direct3D. On platforms withnative depth textures it linearizes and expands the value to match camera’s range.
返回深度纹理值在眼空间的深度。i为从深度纹理中取样得到的值
z-buffer值不是线性的。
opengl 中是一个 0-1的值。0近1远，
directx中是一个-1到1 的值
Linear01Depth参数是0-1的深度值，可得最后计算结果为z/f;就是说，是将[0, f]映射到[0,1]空间，若要映射[n, f]到[0, 1]则是(z-n)/(f-n)。
LinearEyeDepth中参数是0-1的深度值，可得最后计算结果为z。很明显，LinearEyeDepth是将经过透视投影变换的深度值还原了。DECODE_EYEDEPTH跟该函数实现一样