Open Shading Language

Open Shading Language (OSL) is a programmable shading system developed for advanced rendering engines. It allows technical artists and developers to write custom shader code using a C-like scripting language.

In Blender, OSL can be used within Cycles to define custom surface, volume, and displacement shaders. This gives users full control over shading behavior, enabling procedural effects, advanced lighting models, and custom geometry-based material logic that may not be possible with built-in shader nodes alone.

Unlike node-based materials, OSL shaders are authored as text scripts using Blender's internal Text Editor or loaded from external .osl or .oso files. These scripts are then compiled and used in the Shader Editor through the Script Node.

Tip

OSL is especially useful for generating procedural textures, custom BRDFs, or implementing research prototypes. It also allows sharing shaders across compatible rendering applications that support the OSL standard.

使用方法

To use Open Shading Language (OSL) in Blender, follow these steps:

  1. Enable OSL Rendering

    In the Render Properties enable Open Shading Language.

  2. Add a Script Node

    In the Shader Editor add Script Node then in the node's properties:

    • Set the Mode to Internal to use a Blender text data-block, or

    • Set it to External to load a shader file from disk (either .osl or compiled .oso).

    For the internal mode, create a new text data-block in the Text Editor, then write or paste your OSL code there.

    Blender will compile the OSL source file automatically. If the source is .osl, it will be compiled into .oso bytecode. Compilation errors will be shown in the system console.

  3. Use Shader Outputs

    Once compiled, the node's outputs will reflect the output parameters defined in the OSL code. These outputs can be connected to any part of the material node tree.

シェーダーを記述する

For more details on how to write shaders, see the OSL Documentation.

Here is a simple example:

shader simple_material(
    color Diffuse_Color = color(0.6, 0.8, 0.6),
    float Noise_Factor = 0.5,
    output closure color BSDF = diffuse(N))
{
    color material_color = Diffuse_Color * mix(1.0, noise(P * 10.0), Noise_Factor);
    BSDF = material_color * diffuse(N);
}

クロージャ

OSL is different from, for example, RSL or GLSL, in that it does not have a light loop. There is no access to lights in the scene, and the material must be built from closures that are implemented in the renderer itself. This is more limited, but also makes it possible for the renderer to do optimizations and ensure all shaders can be importance sampled.

The available closures in Cycles correspond to the shader nodes and their sockets; for more details on what they do and the meaning of the parameters, see the shader nodes manual.

参考

Documentation on OSL's built-in closures.

BSDF

  • diffuse(N)

  • oren_nayar(N, roughness)

  • diffuse_ramp(N, colors[8])

  • phong_ramp(N, exponent, colors[8])

  • diffuse_toon(N, size, smooth)

  • glossy_toon(N, size, smooth)

  • translucent(N)

  • reflection(N)

  • refraction(N, ior)

  • transparent()

  • microfacet_ggx(N, roughness)

  • microfacet_ggx_aniso(N, T, ax, ay)

  • microfacet_ggx_refraction(N, roughness, ior)

  • microfacet_beckmann(N, roughness)

  • microfacet_beckmann_aniso(N, T, ax, ay)

  • microfacet_beckmann_refraction(N, roughness, ior)

  • ashikhmin_shirley(N, T, ax, ay)

  • ashikhmin_velvet(N, roughness)

Hair(ヘアー)

  • hair_reflection(N, roughnessu, roughnessv, T, offset)

  • hair_transmission(N, roughnessu, roughnessv, T, offset)

  • principled_hair(N, absorption, roughness, radial_roughness, coat, offset, IOR)

BSSRDF (双方向散乱面反射率分布関数)

Used to simulate subsurface scattering.

bssrdf(method, N, radius, albedo)
パラメータ:

  • method (string) --

    サブサーフェススキャタリングをシミュレートするレンダリング方法。

    • burley: An approximation to physically-based volume scattering. This method is less accurate than random_walk however, in some situations this method will resolve noise faster.

    • random_walk_skin: Provides accurate results for thin and curved objects. Random Walk uses true volumetric scattering inside the mesh, which means that it works best for closed meshes. Overlapping faces and holes in the mesh can cause problems.

    • random_walk: Behaves similarly to random_walk_skin but modulates the Radius based on the Color, Anisotropy, and IOR. This method thereby attempts to retain greater surface detail and color than random_walk_skin.

  • N (vector) -- Normal vector of the surface point being shaded.

  • radius (vector) -- 光がサーフェスの下を散乱する平均距離。半径が大きいほど、光が影に流れ込み、オブジェクトを通過するため、柔らかな外観になります。散乱距離はRGBチャネルに対して個別に指定され、赤い光がより深く散乱する皮膚などのマテリアルをレンダリングします。X、Y、Zの値は、それぞれR、G、Bの値にマッピングされます。

  • albedo (color) -- Color of the surface, or physically speaking, the probability that light is reflected for each wavelength.

Volume(ボリューム)

  • henyey_greenstein(g)

  • absorption()

その他

  • emission()

  • ambient_occlusion()

  • holdout()

  • background()

Attributes(属性)

Geometry attributes can be read through the getattribute() function. This includes UV maps, color attributes and any attributes output from geometry nodes.

The following built-in attributes are available through getattribute() as well.

geom:generated

Automatically generated texture coordinates, from non-deformed mesh.

geom:uv

デフォルトで出力される UV マップ。

geom:tangent

Default tangent vector along surface, in object space.

geom:undisplaced

Position before displacement, in object space.

geom:dupli_generated

For instances, generated coordinate from instancer object.

geom:dupli_uv

For instances, UV coordinate from instancer object.

geom:trianglevertices

Three vertex coordinates of the triangle.

geom:numpolyvertices

ポリゴンを形成する頂点の数(現在 3 を常に返します)。

geom:polyvertices

ポリゴンを形成する頂点の座標系の配列 (現在は常に 3 頂点を対象とします)。

geom:name

オブジェクトの名称。

geom:is_smooth

Is mesh face smooth or flat shaded.

geom:is_curve

Is object a curve or not.

geom:curve_intercept

0..1 coordinate for point along the curve, from root to tip.

geom:curve_thickness

Thickness of the curve in object space.

geom:curve_length

Length of the curve in object space.

geom:curve_tangent_normal

ストランドの Tangent 法線。

geom:is_point

Is point in a point cloud or not.

geom:point_radius

Radius of point in point cloud.

geom:point_position

Center position of point in point cloud.

geom:point_random

Random number, different for every point in point cloud.

path:ray_length

最後に衝突してからの光線の距離。

object:random

Random number, different for every object instance.

object:index

Object unique instance index.

object:location

オブジェクトの位置。

material:index

Material unique index number.

particle:index

Particle unique instance number.

particle:age

フレームにおけるパーティクルエージ。

particle:lifetime

フレームにおける総表示時間。

particle:location

パーティクルの位置。

particle:size

Size of the particle.

particle:velocity

パーティクルの速度。

particle:angular_velocity

パーティクルの角速度。

Trace (トレース)

CPU Only

私達は OSL シェーダーからの光線をトレースできるよう、trace(point pos, vector dir, ...) 関数をサポートしています。現時点では "shade" パラメータはサポートされていませんが、衝突したオブジェクトの属性値は getmessage("trace", ..) 関数を用いることで取得できます。どのようにこの機能を用いるかに関する詳細は OSL 仕様書を参照下さい。

この機能はライティングの代替として利用できる物ではありません;主な目的はシェーダーに、例えば立体に遮蔽されうる投影テクスチャを適用したり、露出した立体をより "摩耗させ" たりする等その他アンビエントオクルージョンのような効果を作り、近接した立体を "検知させる" 事です。

Metadata(メタデータ)

Metadata on parameters controls how they are displayed in the user interface. The following metadata entries are supported:

[[ string label = "My Label" ]]

Custom display name of the parameter in the user interface.

[[ string widget = "null" ]]

Hides the parameter from the user interface.

[[ string widget = "boolean" ]] or [[ string widget = "checkbox" ]]

Displays an integer parameter as a boolean checkbox.

[[ string widget = "filename" ]]

Displays the parameter as a file path selector.

[[ string widget = "mapper", string options = "left:0|right:1" ]]

Displays an integer parameter as an enumerated menu. The options string defines a list of label-value pairs separated by |.

[[ string vecsemantics = "POINT" ]]

Marks a vector parameter as a translation input (position vector).

[[ string vecsemantics = "NORMAL" ]]

Marks a vector parameter as a normal input (direction vector).

[[ string unit = "radians" ]]

Marks a float parameter as an angle input, displayed in radians.

[[ string unit = "m" ]]

Marks a float parameter as a distance input, displayed in meters.

[[ string unit = "mm" ]]

Marks a float parameter as a distance input, displayed in millimeters.

[[ string unit = "s" ]] or [[ string unit = "sec" ]]

Marks a float parameter as a time input, displayed in seconds.

制限

重要

OSL is not supported with GPU rendering unless using the OptiX backend.

Some OSL features are not available when using the OptiX backend. Examples include:

  • Texture lookups require OSL to be able to determine a constant image file path for each

    texture call.

  • Some noise functions are not available. Examples include Cell, Simplex, and Gabor.

  • The trace function is not functional. As a result of this, the Ambient Occlusion and Bevel nodes do not work.