http://docs.unity3d.com/Manual/SL-SurfaceShaders.html

一：surface shader是啥

Writing shaders that interact with lighting is complex. There are different light types, different shadow options, different rendering paths (forward and deferred rendering), and the shader should somehow handle all that complexity.

Surface Shaders in Unity is a code generation approach that makes it much easier to write lit shaders than using low levelvertex/pixel shader programs. Note that there are no custom languages, magic or ninjas involved in Surface Shaders; it just generates all the repetitive code that would have to be written by hand. You still write shader code in Cg / HLSL.

就是说直接写shader太复杂，为了提高效率，使用了surface shader，“using low levelvertex/pixel shader programs”，surface shader不是一种定义的语言，只是VS PS的上层，surface shader编译后还是会转化为相应的vs ps的。从u3d编辑器的"show generated code"中也可以看出来。

同样的，输入输出，“Standard output structure of surface shaders is this:”

标准的输出是：

struct SurfaceOutput
{fixed3 Albedo;  // diffuse colorfixed3 Normal;  // tangent space normal, if writtenfixed3 Emission;half Specular;  // specular power in 0..1 rangefixed Gloss;    // specular intensityfixed Alpha;    // alpha for transparencies
};

　　u3d5中又新加了SurfaceOutputStandard和SurfaceOutputStandardSpecular输出

二：编译指令：

和其他shader一样，也是在“CGPROGRAM..ENDCG block”块内部的，区别是：

• It must be placed inside SubShader block, not inside Pass. Surface shader will compile into multiple passes itself.
• It uses #pragma surface ... directive to indicate it’s a surface shader.

　　1.置在SubShader内，surface shader会自动编译进多pass

　　2.使用#pragma surface指令来告知俺是surface shader;#pragma surface surfaceFunction lightModel [optionalparams]

三：输入结构：

The input structure Input generally has any texture coordinates needed by the shader. Texture coordinates must be named “uv” followed by texture name (or start it with “uv2” to use second texture coordinate set).

纹理坐标名必须使用 uv开头，后面跟上纹理名

• float3 viewDir - will contain view direction, for computing Parallax effects, rim lighting etc.
• float4 with COLOR semantic - will contain interpolated per-vertex color.
• float4 screenPos - will contain screen space position for reflection or screenspace effects.
• 已经定义好了屏幕坐标...不要在WVP了...
• float3 worldPos - will contain world space position.
• float3 worldRefl - will contain world reflection vector if surface shader does not write to o.Normal. See Reflect-Diffuse shader for example.
• float3 worldNormal - will contain world normal vector if surface shader does not write to o.Normal.
• float3 worldRefl; INTERNAL_DATA - will contain world reflection vector if surface shader writes to o.Normal. To get the reflection vector based on per-pixel normal map, use WorldReflectionVector (IN, o.Normal). See Reflect-Bumped shader for example.
• float3 worldNormal; INTERNAL_DATA - will contain world normal vector if surface shader writes to o.Normal. To get the normal vector based on per-pixel normal map, use WorldNormalVector (IN, o.Normal).

总结：surface shader为了快速开发。预先定义好了output和input结构；一些常见光源。