Writing Surface Shaders

Написание шейдеров, взаимодействующих с освещением, это сложная задача. Есть различные типы источников света, различные варианты теней, различные пути рендеринга - прямой (forward) и отложенный (deferred), и шейдер должен как-то управлять всей этой сложностью.

Surface Shaders in Unity is a code generation approach that makes it much easier to write lit shaders than using low level vertex/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 HLSL.

For some examples, take a look at Surface Shader Examples and Surface Shader Custom Lighting Examples.

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.

Затем компилятор поверхностного шейдера выясняет, какие требуются входящие данные, какие заполняются исходящие данные и т.д., и генерирует итоговые вершинные и пиксельные шейдеры, а также проходы рендеринга для обработки упреждающего и отложенного рендеринга.

Вот стандартная исходящая структура поверхностных шейдеров:

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

Поверхностный шейдер размещён в блоке CGPROGRAM..ENDCG, как и любой другой шейдер. Отличия:

• Он должен быть размещён в блоке SubShader, не в Pass. Поверхностный шейдер сам по себе будет скомпилирован в несколько проходов.
• Он использует директиву #pragma surface ... для обозначения, что он является поверхностным шейдером.

Директива #pragma surface:

#pragma surface surfaceFunction lightModel [optionalparams]

Required parameters

• surfaceFunction - which Cg function has surface shader code. The function should have the form of void 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 based Standard and StandardSpecular, as well as simple non-physically based Lambert (diffuse) and BlinnPhong (specular). See Custom Lighting Models page for how to write your own.
  • Standard lighting model uses SurfaceOutputStandard output struct, and matches the Standard (metallic workflow) shader in Unity.
  • StandardSpecular lighting model uses SurfaceOutputStandardSpecular output struct, and matches the Standard (specular setup) shader in Unity.
  • Lambert and BlinnPhong lighting 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.

• alpha or alpha:auto - Will pick fade-transparency (same as alpha:fade) for simple lighting functions, and premultiplied transparency (same as alpha: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 use addshadow directive 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 Examples
• decal: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 - Пользовательская функция модификации финального цвета. См. Примеры поверхностных шейдеров.
• finalgbuffer:ColorFunction - Custom deferred path for altering gbuffer 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 - использовать DX11 GPU тесселяцию; функция рассчитывает факторы тесселяции. См. страницу Поверхностные шейдеры с использованием тесселяции для подробностей.

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 - Отключает аддитивный проход упреждающего рендеринга. Шейдер будет поддерживать один направленный источник света и все остальные источники света будут рассчитываться повершинно или как сферические гармоники. Также делает шейдер меньше.
• nolppv - Disables Light Probe Proxy Volume support in this shader.
• noshadowmask - Disables Shadowmask support for this shader (both Shadowmask and Distance Shadowmask).

Miscellaneous options

• softvegetation - Поверхностный шейдер будет рендериться только при включенной опции Soft Vegetation (мягкая растительность).
• interpolateview - Compute view direction in the vertex shader and interpolate it; instead of computing it in the pixel shader. This can make the pixel shader faster, but uses up one more texture interpolator.
• halfasview - Передавать полу-направленный вектор в функцию освещения вместо вектора по направлению взгляда. Полу-направленный будет рассчитан и нормализован для каждой вершины. Это быстрее, но не совсем точно.
• approxview - Removed in Unity 5.0. Use interpolateview instead.
• dualforward - Use dual lightmaps in forward rendering path.
• dithercrossfade - Makes the surface shader support dithering effects. You can then apply this shader to GameObjects that use an LOD Group component configured for cross-fade transition mode.

To see what exactly is different from using different options above, it can be helpful to use “Show Generated Code” button in the Shader Inspector.

Surface Shader input structure

Входящая структура Input, как правило, содержит любые текстурные координаты, необходимые шейдеру. Текстурные координаты должны именоваться “uv” + имя текстуры (или начинайте с “uv2” для использования второго набора текстурных координат).

Дополнительные значения, которые можно поместить в структуру Input:

• float3 viewDir - contains view direction, for computing Parallax effects, rim lighting etc.
• float4 with COLOR semantic - 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 using ComputeGrabScreenPos function.
• 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, use WorldReflectionVector (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, use WorldNormalVector (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 Shading Language pages for details.

• 2017–06–08 Page published

• noshadowmask added in 5.6