Unity Standard surface structure doc
https://docs.unity3d.com/Manual/SL-SurfaceShaders.html
Surface Shader input structure
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).
Additional values that can be put into Input structure:
float3 viewDir- contains view direction, for computing Parallax effects, rim lighting etc.float4withCOLORsemantic - contains interpolated per-vertex color.float4 screenPos- contains screen space position for reflection or screenspace effects. Note that this is not suitable for GrabPass; you need to compute custom UV yourself usingComputeGrabScreenPosfunction.float3 worldPos- contains world space position.float3 worldRefl- contains world reflection vector if surface shader does not write to o.Normal. See Reflect-Diffuse shader for example.float3 worldNormal- contains world normal vector if surface shader does not write to o.Normal.float3 worldRefl; INTERNAL_DATA- contains world reflection vector if surface shader writes to o.Normal. To get the reflection vector based on per-pixel normal map, useWorldReflectionVector (IN, o.Normal). See Reflect-Bumped shader for example.float3 worldNormal; INTERNAL_DATA- contains world normal vector if surface shader writes to o.Normal. To get the normal vector based on per-pixel normal map, useWorldNormalVector (IN, o.Normal).
Surface Shaders and DirectX 11 HLSL syntax
Currently some parts of surface shader compilation pipeline do not understand DirectX 11-specific HLSL syntax, so if you’re using HLSL features like StructuredBuffers, RWTextures and other non-DX9 syntax, you have to wrap it into a DX11-only preprocessor macro.
See Platform Specific Differences and Using HLSL pages for details.
How it works
You define a “surface function” that takes any UVs or data you need as input, and fills in output structure SurfaceOutput. SurfaceOutput basically describes properties of the surface (it’s albedo color, normal, emission, specularity etc.). You write this code in HLSL.
Surface Shader compiler then figures out what inputs are needed, what outputs are filled and so on, and generates actual vertex&pixel shaders, as well as rendering passes to handle forward and deferred rendering.
Standard output structure of surface shaders is this:
struct SurfaceOutput
{
fixed3 Albedo; // diffuse color
fixed3 Normal; // tangent space normal, if written
fixed3 Emission;
half Specular; // specular power in 0..1 range
fixed Gloss; // specular intensity
fixed Alpha; // alpha for transparencies
};
In Unity 5, surface shaders can also use physically based lighting models. Built-in Standard and StandardSpecular lighting models (see below) use these output structures respectively:
struct SurfaceOutputStandard
{
fixed3 Albedo; // base (diffuse or specular) color
fixed3 Normal; // tangent space normal, if written
half3 Emission;
half Metallic; // 0=non-metal, 1=metal
half Smoothness; // 0=rough, 1=smooth
half Occlusion; // occlusion (default 1)
fixed Alpha; // alpha for transparencies
};
struct SurfaceOutputStandardSpecular
{
fixed3 Albedo; // diffuse color
fixed3 Specular; // specular color
fixed3 Normal; // tangent space normal, if written
half3 Emission;
half Smoothness; // 0=rough, 1=smooth
half Occlusion; // occlusion (default 1)
fixed Alpha; // alpha for transparencies
};
Samples
See Surface Shader Examples, Surface Shader Custom Lighting Examples and Surface Shader Tessellation pages.
Surface Shader compile directives
Surface shader is placed inside CGPROGRAM..ENDCG block, just like any other shader. The differences are:
- 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.
The #pragma surface directive is:
#pragma surface surfaceFunction lightModel [optionalparams]
Required parameters
surfaceFunction- which Cg function has surface shader code. The function should have the form ofvoid surf (Input IN, inout SurfaceOutput o), where Input is a structure you have defined. Input should contain any texture coordinates and extra automatic variables needed by surface function.lightModel- lighting model to use. Built-in ones are physically basedStandardandStandardSpecular, as well as simple non-physically basedLambert(diffuse) andBlinnPhong(specular). See Custom Lighting Models page for how to write your own.Standardlighting model usesSurfaceOutputStandardoutput struct, and matches the Standard (metallic workflow) shader in Unity.StandardSpecularlighting model usesSurfaceOutputStandardSpecularoutput struct, and matches the Standard (specular setup) shader in Unity.LambertandBlinnPhonglighting models are not physically based (coming from Unity 4.x), but the shaders using them can be faster to render on low-end hardware.
Optional parameters
Transparency and alpha testing is controlled by alpha and alphatest directives. Transparency can typically be of two kinds: traditional alpha blending (used for fading objects out) or more physically plausible “premultiplied blending” (which allows semitransparent surfaces to retain proper specular reflections). Enabling semitransparency makes the generated surface shader code contain blending commands; whereas enabling alpha cutout will do a fragment discard in the generated pixel shader, based on the given variable.
alphaoralpha:auto- Will pick fade-transparency (same asalpha:fade) for simple lighting functions, and premultiplied transparency (same asalpha:premul) for physically based lighting functions.alpha:blend- Enable alpha blending.alpha:fade- Enable traditional fade-transparency.alpha:premul- Enable premultiplied alpha transparency.alphatest:VariableName- Enable alpha cutout transparency. Cutoff value is in a float variable with VariableName. You’ll likely also want to useaddshadowdirective to generate proper shadow caster pass.keepalpha- By default opaque surface shaders write 1.0 (white) into alpha channel, no matter what’s output in the Alpha of output struct or what’s returned by the lighting function. Using this option allows keeping lighting function’s alpha value even for opaque surface shaders.decal:add- Additive decal shader (e.g. terrain AddPass). This is meant for objects that lie atop of other surfaces, and use additive blending. See Surface Shader Examplesdecal:blend- Semitransparent decal shader. This is meant for objects that lie atop of other surfaces, and use alpha blending. See Surface Shader Examples
Custom modifier functions can be used to alter or compute incoming vertex data, or to alter final computed fragment color.
vertex:VertexFunction- Custom vertex modification function. This function is invoked at start of generated vertex shader, and can modify or compute per-vertex data. See Surface Shader Examples.finalcolor:ColorFunction- Custom final color modification function. See Surface Shader Examples.finalgbuffer:ColorFunction- Custom deferred path for altering G-buffer content.finalprepass:ColorFunction- Custom prepass base path.
Shadows and Tessellation - additional directives can be given to control how shadows and tessellation is handled.
addshadow- Generate a shadow caster pass. Commonly used with custom vertex modification, so that shadow casting also gets any procedural vertex animation. Often shaders don’t need any special shadows handling, as they can just use shadow caster pass from their fallback.fullforwardshadows- Support all light shadow types in Forward rendering path. By default shaders only support shadows from one directional light in forward rendering (to save on internal shader variant count). If you need point or Spot Light shadows in forward rendering, use this directive.tessellate:TessFunction- use DX11 GPU tessellation; the function computes tessellation factors. See Surface Shader Tessellation for details.
Code generation options - by default generated surface shader code tries to handle all possible lighting/shadowing/lightmap scenarios. However in some cases you know you won’t need some of them, and it is possible to adjust generated code to skip them. This can result in smaller shaders that are faster to load.
exclude_path:deferred,exclude_path:forward,exclude_path:prepass- Do not generate passes for given rendering path (Deferred Shading, Forward and Legacy Deferred respectively).noshadow- Disables all shadow receiving support in this shader.noambient- Do not apply any ambient lighting or light probes.novertexlights- Do not apply any light probes or per-vertex lights in Forward rendering.nolightmap- Disables all lightmapping support in this shader.nodynlightmap- Disables runtime dynamic global illumination support in this shader.nodirlightmap- Disables directional lightmaps support in this shader.nofog- Disables all built-in Fog support.nometa- Does not generate a “meta” pass (that’s used by lightmapping & dynamic global illumination to extract surface information).noforwardadd- Disables Forward rendering additive pass. This makes the shader support one full directional light, with all other lights computed per-vertex/SH. Makes shaders smaller as well.nolppv- Disables Light Probe Proxy Volume support in this shader.noshadowmask- Disables Shadowmask support for this shader (both Shadowmask and Distance Shadowmask).
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