Advanced car-paint OSL shader

cglSurfaceCarPaint is an advanced car-paint OSL shader, free to download from CG-Lion studio’s website.

The cglSurfaceCarPaint car-paint material combines 3 layers:
Base: A blend of diffuse/metallic shading with a view-angle color mix
Metallic flakes: Distance blended procedural metallic flakes
Clear coat: Glossy clear coat layer with built-in procedural bump irregularity
And has been tested with:
Blender & Cycles
Maya & Arnold
3ds max & V-Ray

Download and more info

Getting started with OSL shaders


Using OSL Shaders in Arnold for Maya

Maya 2020 | Arnold 6

Autodesk Maya 2020 & Arnold 6 offer a flexible OSL development and usage workflow.
You can both load or write OSL shaders on the fly, compile, test, and render them,
And also define a shader folder path for shaders to be available as part of your library for all projects.
Steps for using OSL shaders in Maya & Arnold:

Writing an OSL shader or loading it for single use (just the current project):

  1. Create a new aiOslShader node:
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  2. Select the new aiOslShader node and in its attributes either write new OSL code in the code OSL Code section, or press Import to Load an OSL shader file (*.osl):
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  3. When new shader code is imported, it’s automatically compiled:
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  4. I f you’ve written new code, or changed the code it will have to be re-compiled.
    In that case press Compile OSL Code:
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  5. The code may contain errors, in that case you will see a red Compile Failure message:
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    You can read the error message in the Maya output window, or in the Maya Script Editor, Correct the code and press Compile OSL Code again.
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  6. After the OSL code is compiled successfully, the shader’s input parameters can be accessed in the OSL Attributes section below the code:
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  7. Depending on the type of output the OSL shader generates, the aiOSLShader node should to be connected to an input in the object’s shader graph or Shading Group.
    * OSL shaders can be surface shaders, volume shaders, procedural textures, texture processors and more..
    To Apply the OSL shader to an object as a surface shader, disconnect the object’s current surface shader if it has one,
    And then drag and drop the aiOSLShader node from the Hypershade window onto the object.
    In the Connection Editor select outValue on the left side (node outputs) and surfaceShader in the right side (object inputs):
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When compiling OSL shaders “on the fly” using the above steps, the shader’s input parameters don’t necessarily appear at their intended order that is  defined in the shader code.


Installing OSL shaders so they will always be available as custom nodes in the Hypershade library

  1. Create a folder for storing your OSL shaders, and place you OSL shader files (*.osl) in this folder.
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  2. Locate Maya’s Maya.env file.
    This is an ascii text file containing environment variables that Maya loads at startup.
    The Maya.env will usually be located at:
    C:\Users\<your user>\Documents\maya\<maya version>
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  3. Open Maya.env in a text editor and add the following line to it:
    ARNOLD_PLUGIN_PATH=<path to your OSL shaders folder>
    for example:
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  4. Restart Maya.
    When Maya loads, the MtoA (Maya to Arnold) plugin will automatically compile the shaders that are found in the folder, report about the compilations or found errors in the Maya output window, and create compiled *.oso files for each shader:
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  5. The compiled shaders will now be available as custom nodes in the Hypershade Arnold library with the typical “ai” (Arnold Interface) prefix added to their names:
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  6. The OSL shaders will be created as nodes with their editable attributes, that can be connected to an object’s shading network graph:
    * Connecting the node to the graph is the same as described in the previous part (7)
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  1. OSL read-list
  2. What are OSL Shaders?
  3. Using OSL shaders in V-Ray for 3ds max
  4. Using OSL shaders in Blender & Cycles
  5. Writing a basic OSL color shader

What are OSL shaders?

OSL is an acronym for Open Shading Language.
Developed Originally at Sony Pictures Imageworks for the Arnold render engine, Open Shading language is a C like programming language with which custom material, textures and shading effects can be developed OSL shaders (*.osl files), that are supported many by popular render engines.

OSL allows development of complex texturing and shading effects using scene input parameters like the shading point’s world position vector, normal vector, UV coordinates etc., and optical ray-tracing  functions – BSDF*’s or “Color Closures” as they are called in OSL, like Diffuse, Glossy, Refraction light scattering etc. that can be combined with C  logic and math programming.

*.osl files are compiled to *.oso file for rendering.
Most render engines supporting OSL shaders ship with an OSL compiler.


Useful OSL shader libraries found on the web:

> OSL Shaders for download on the Chaos Group website:

> OSL Shaders for download at the Autodesk Developer Network Github repository:
These are the OSL shaders that ship with 3ds max 2019 or newer, and are providing texture and pattern processing tools, but not materials.
* Material shaders or “Closures” as they are referred to in OSL are not supported by 3ds max’s native implementation of OSL.

> A library of OSL shaders collected by Shane Ambler:



  1. In general, OSL shaders are supported only in CPU Rendering, but not supported by GPU renderers. There are some attempts to develop OSL support for GPU renderers, But as far as I know they are limited.
  2. Some OSL shaders will work on one or more render engines, and not work as expected on other render engines. the reason being that each render engine has it’s own implementation of OSL.
    These differences may show in a different rendered result and also compile failure.


Basic example:
The following example renders show how a combination of two basic OSL shaders iv’e written, one of which is a dielectric material shader, and the other a color/angle blend procedural texture, produce fairly consistent results when rendered in different render engines.
* note the difference in specular glossy roughness interpretation for the same 0.1 value..

> You’r welcome to download these two basic OSL shaders here.

Arnold for Maya:
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V-Ray for 3ds max:
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Cycles for Blender:
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  1. OSL read-list
  2. Using OSL shaders in Arnold for Maya
  3. Using OSL shaders in V-Ray for 3ds max
  4. Using OSL shaders in Blender & Cycles
  5. Writing a basic OSL color shader

Understanding Transparency Render Settings

In theory, all clear* refractive surfaces should have their shadow calculated using a refractive caustics calculation in-order to render the refractive lensing** effect correctly, have their transparency color calculated as volumetric absorption of light through the medium in-order to render the color correctly for areas of different thickness, and have not only external reflections, but also internal reflections calculated, in-order to render the interaction between light and the transparent body correctly.
However, for thin surfaces of even thickness, like window glazing and car windshields, these optical effects can be rendered in much cheaper (non physical) methods, with very little compromise on final image quality or look, and even have an easier setup in most cases.
For this reason most popular render engines have object (mesh) and material (shader) parameters that allow configuration of the way these transparency effects will be rendered.
In this short article we’ll cover the different methods for rendering transparency effects, the reasoning behind them and the way to configure these settings in different render-engines.

In the comparison images below (rendered with Cycles), the images on the left were rendered with physically correct glass settings, 8192 samples + denoising,
And the images on the right were rendered with “flat” transparency settings and 1024 samples + denoising.
> See the shader settings below
Note that while for the monkey statue, the fast flat transparency settings produce an unrealistic result, the window glazing model loses very little of its look with the flat fast settings:


Lensing, caustics and transparent shadows:


It’s a common intuitive mistake, that transparent objects don’t cast shadows, but they actually do. they don’t block light, they change its direction. light is refracted through them, gets focused in some areas of their surroundings (caustics) but can’t pass through them directly, so a shadow is created.
A good example of this would be a glass ball, acting like a lens, focusing the light into a tiny area, and otherwise having a regular elliptical shadow. if we tell the render-engine to just let direct light pass through the object we won’t get a correct realistic result, even if the light gets colored by the object’s transparency color.
There is however one case where letting the direct light simply pass through the object can both look correct and save a lot of calculations, and that is when the object is a thin surface with consistent thickness like window glazing.
So in many popular render-engines, when rendering an irregular thick solid transparent body like a glass statue or a glass filled with liquid, we have to counter-intuitively set the object or material to be opaque for direct light and let the indirect refracted light (caustics) create the correct lensing effect (focused light patterns in the shadow area)
> physically, light passing through a material medium is always refracted, i.e. indirect light. but for thin surfaces with even thickness like glazing, the lensing effect is insignificant, and can be completely disregarded by letting light pass directly through the object and be rendered as ‘transparent shadow’.
So the general rule regarding calculating caustics (lensing) vs casting transparent shadows (non physical), is that if the transparent object is a solid irregular shape with varying thickness like a statue or a bottle of liquid it should be rendered as opaque for direct light but with fully calculated caustics i.e. refracted indirect light.

Transparency color:


Physically, the color of transparency*** is always created by volumetric absorption of light traveling within the material medium. as light travels further through a material, more and more of it’s energy gets absorbed in the medium**** (converted to heat), therefore the thicker the object, less light will reach its other side, and it will appear darker. this volumetric absorption of light isn’t consistent for all wave lengths (colors) of light so the object appears to have a color.
For example, common glass, absorbs the red and blue light at a higher rate than green light, and therefore objects seen through it will appear greenish. when we look at the thin side of a common glazing surface we see a darker green color because we see light that has traveled through more glass (through a thicker volume of glass) because of refraction bending the light into the length of the surface. tea, in a glass, generally looks dark orange-brown, but if spilled on the floor it will ‘lose’ its color, and look clear like water because spilled on the floor, it’s too thin to absorb a significant amount of light and appear to have a color.
Most render engines allow setting the transparency (“refraction”/”transmission”) color of the material both as a ‘flat’ non physical filter color, and as a physical RGB light absorption rate (sometimes referred to as ‘fog’ color), that can in some cases be more accurately tuned by additional multiplier or depth parameters.
Setting an object’s transparency color using physical absorption (fog) usually requires more tweaking because in this method, the final rendered color is dependent not only on the color we set at the material/shader, but also on the model’s actual real world thickness.*****
In general, the transparency color of thick, solid, irregularly shaped objects (with varying thickness) must be set as a physical absorption rate color, and not as a simple filter color, otherwise the resulting color will not be affected by the material thickness, and look wrong.
For thin surfaces with consistent thickness, like window glazing, however, it’s more efficient to setup the transparency color as a ‘flat’ filter color, because it’s more convenient and predictable to setup, and produced a correct looking result.
For example, if we need to render an Architectural glazing surface that will filter exactly 50 percent of the light passing through it, it’s much simpler to set it up using a simple 50% grey transparency filter color, because this method disregards the glass model’s thickness. This approach isn’t physical, but for an evenly thick glazing surface, the result has no apparent difference from a physical volumetric absorption approach to the same task.

Internal reflections:


It’s not intuitive to think that the air surface itself has reflections when seen through a transparent material volume like water or glass.
Viewed from under water, the air surface above, acts like a mirror for certain angles, reflecting objects that are under water. a glass ball lit by a lamp has a very distinct highlight, which is the reflected image of the light source itself (specular reflection), but it also has an internal highlight appearing on inside where the glass volume meets the air volume. we can easily ‘miss’ this internal highlight because in many cases it’s appearance converges with the bright focused light behind the ball, caused lensing (refractive caustics). the distinctly shiny appearance of diamonds, for example, is very much dependent on bright internal reflections, diamond cutting patterns are specifically designed to reflect a large percentage of light back to the viewer and look shiny, and if we wish to create a realistic rendering of diamonds, we will not only have to setup the correct refractive index for the material, but also model the geometric shape of the diamond correctly, and of course, set the material to render both external (“regular”******) reflections and internal reflections.
Your probably already guessing what I’m about to say next..
For thin surfaces with even thickness, the internal reflection is barely noticeable, because it converges with the main surface reflection, an for this reason, when rendering window glazing, car windshields, and the like, we can usually turn the internal reflections calculation off to save render time.


Render Settings:

Simplified settings summary table:

Flat (Glazing) Physical (irregular volume)
Shadow Transparent Caustics
Color Filter Volumetric Absorption
Reflections External only External and Internal

Example Cycles (Blender) shaders:
> The Flat glazing shader is actually more complex to define since it involves defining different types of calculations per different type of rays being traced (cheating).
In general, for Shadow and Diffuse rays that shader is calculated as a simple Transparent shader and nor a refraction shader, and when back-facing, the shader is calculated as pure white transparent instead of glossy to remove the internal reflections.
> While the flat glazing shader is only connected to the Surface input of the material output, the physical glass shader has also a Volume Absorption BSDf node connected to the Volume input of the material output node.
> Note that a simple Principled BSDF material will have flat transparency and physical shadow (caustics) by default.
> For caustics to be calculated, the Refractive Caustics option has to be enabled in the Light Path > Caustics settings in the Cycles render settings.


Example V-Ray Next for 3ds max material settings:
In V-Ray for 3ds max (and Maya) the Affect Shadows parameter in the VrayMtl Refraction settings determines weather the shadows will be fake transparent shadows suitable for glazing or (on) or opaque (off) which is the suitable setting for caustics.
> The caustics calculation is either GI Caustics which is activated by default in the main GI settings or a dedicated Caustics calculation that can be activated, also in the GI settings.
> For flat glazing the color is defined as Refraction Color and for physical glass the Refraction color is pure white and the glass color is set as Fog color.


Example Arnold for Maya settings:
> In Arnold 5 for Maya the Opaque setting in the shape node Arnold attributes must be unchecked for transparent shadows, and checked for opaque shadows suitable for caustics.
> For rendering refractive caustics in Arnold for Maya more settings are needed.
> When the Transmission Depth attribute is set to 0 the Transmission Color will be rendered as flat filter color, and when the Transmission Depth attribute is a value higher than 0 the transparency color will be calculated as volumetric absorption reaching the Transmission Color at the specified depth.


General notes:

> in Brute Force Path Tracers like Cycles and Arnold the Caustics calculation is actually a Diffuse indirect light path. this seems un-intuitive, but the light pattern appearing on a table surface in the shadow of a transparent glass is actually part of the table surface’s diffuse reflection phenomenon.

> what we refer to as ‘Diffuse Color’ in dielectric (non-metals) is actually a simplification of absorption of light scattered inside the object volume (SSS).

* Optically all dielectric materials (non-metals) are refractive, but not all of them are also clear, the is, most of them actually have micro particles or structures within their volume, that scatter and absorb light that travels through them, creating the effects we’re used to refer to as “Subsurface Scattering” (SSS) and in the higher densities “Diffuse reflection”.

** Lensing is a term used to describe the effect of a material medium bending light, focusing and dispersing it, and so acting as a lens.

*** Actually all color in dielectric (non metallic) materials is created by Volumetric Absorption.

**** Light isn’t only absorbed as it travels through medium, it’s also scattered.

***** Volumetric shading effects usually use the model original scale (the true mesh scale), so to avoid unexpected results it’s best that the object’s transform scale will be 1.0 (or 100% depending on program annotation)

Related Posts:
Cycles Nested Transparencies
Arnold for Maya Refractive Caustics
> Arnold for Maya Transmission Scattering
> Understanding Fresnel Reflections
> Advanced Architectural Glazing shader for Blender
> V-Ray Underwater Rendering

Arnold for 3ds max – Render objects as volumes (volume shading)

3ds max 2019 | Arnold 5

In-order for objects in 3ds max to be rendered as volumes with Arnold, the object mesh has to be converted to a volume, and a Standard Volume material assigned to the object:

  1. Add an Arnold Properties modifier to the object.
  2. Under Volume set the Step Size to a value higher than 0.0.
  3. Assign a Standard Volume material to the object and set it’s parameters to design the volumetric effect:


* Note that both Density and Depth control the transparency or ‘thickness’ of the volume. (lower Depth setting creates a thicker volume)
* When Scattering is set to 0.0 the volume will have only a absorption effect




In this example an Arnold Noise map is connected to the Standard Volume‘s Density parameter:
* Note that the Scale values must be set correctly in order to actually get a ‘cloudy’ effect.
* Note that the noise color values are now controlling the Density of the volume.


Arnold for 3ds max God Rays


Arnold for 3ds max – Volumetric Fog and ‘God Rays’

3ds max 2019 | Arnold 5


Adding a ‘Volume Light’ effect in Arnold for 3ds max is fairly simple:

  1. In the Render Setup windows > Arnold Renderer tab, under Environment, Background & Atmosphere:
  2. Click the Scene Atmosphere material slot, add an Arnold Atmosphere Volume material to it,
    And drag it as an instance to the Material Editor to edit it’s parameters.
  3. Set the Density to a higher than 0.0 value, so the material will have an effect.
  4. You’ll probably need to significantly raise the number of samples in the Atmosphere Volume material, and also the number of Volume samples in the light settings in order to get a clean render.


Arnold for 3ds max Volume Shading

Basic Cloth Material in Arnold for Maya

Maya 2018 | Arnold 5

An example of a basic traditional (not scanned) cloth material setup in Arnold 5 for Maya using an aiStandardSurface shader.


The shading network uses a classic angle dependent color blend to simulate the color of the cloth being washed out at grazing angle of view.

Explanation of the node graph:


  1. A black and white fabric weave texture that will serve as input for multiple shading channels.
    * This is actually not the best example of such a pattern, and could be replaced with a much better texture.
    cotton grey bump
  2. A remapValue node is used to set contrast to the fabric pattern (reduce contrast in this case) prior to it being multiplied with the fabric colors.
    * Note that only one of the textures RGB channels is connected to the remapValue node since it’s a float (mono) processor and not RGB.
    * Note that depending on the fabric texture, you may have to design different curves to achieve the right effect.
  3. Two colors are defined with colorConstant nodes:
    A deep color as the main fabric color, and a washed out color for grazing angle view (“side color”).
  4. An aiFacingRatio node is used as an input for incident angle info.
    * Note that in this case I checked the node’s invert option to make it behave more like other systems I’m used to (if you don’t use invert, the angle blend curve in 5 will be different..)
  5.  A remapValue node used to set the angle blend curve or in other words, how much does the color appears washed out per change of view angle of the cloth surface.
    * The longer it take the curve to become steep from left to right, the more the main color will be dominant before the washed out color will appear.
  6. A colorCorrect node is used in this example just as a way to convert the remapped float value back to RGB for being multiplied with the cloth colors.
    * We could also connect it directly to the individual float components of the RGB colors but this way the node graph is cleaner.
  7. A multiplyDivide node is used to multiply the processed fabric texture with the 2 fabric colors “baking” the pattern into the color.
  8. A blendColors node is used to blend the 2 processed fabric colors together according to the processed facingRatio angle input.
    The result is the final cloth color that is connected to the aiStandardSurface shader.
  9. An aiBump2d node is used to convert the fabric pattern to normal data that will be connected to the aiStandardSurface shader to produce bumps.
  10. An aiStandartSurface shader serving as the main shading node for this material.
    * Note that under Geometry the Thin Walled option is checked so that the Subsurface layer of the shader will act as a Paper Shader rather than SSS.
    * The main cloth color is connected to the SubSurface Color input.


More Arnold shading posts

V-Ray Next’s PBR’ness

3ds max 2019 | V-Ray Next

A quick test of V-Ray Next‘s PBR* workflow,
Namely designing materials while previewing them using V-Ray,
Defining the material properties using the new (to V-Ray) Metalness attribute, and using Roughness rather than Glossiness, shows good results IMO.

* It should be noted that although we got used to referring to the base-color / metallness / Specular material interface as “PBR”, it is actually a principled material interface developed by Disney animations studios.

Results are generally consistent through Blender & Cycles, Maya & Arnold, and UE4.





Related Posts:

  1. V-Ray Next – Metalness
  2. Metal In UE4
  3. Fresnel Reflections

Arnold for Maya – Transmission Scattering (Ray Traced SSS)

Maya 2018 | Arnold 5


The Arnold Standard Surface Shader’s Transmission Scattering options can be used for simulating highly realistic volumetrically ray-traced sub-surface-scattering suitable for materials like wax, soap, milk etc.

While the Transmission Depth attribute controls volumetric light absorption within the object (fog), the Scatter attribute controls what percentage of the light will be scattered instead of absorbed, effectively creating the murky effect of semi-transparent materials.

Note that for the scattering effect to work Scatter must have a dominant percentage value, and the Depth attribute must generally be much lower (shallower) than what would create coloring without scattering, otherwise the object will continue to look transparent and lacking the internal substance that we want to simulate.

Also note that the Opaque attribute must be unchecked in the Arnold attributes of the object’s shape node for the light to be able to pass into the mesh and illuminate the volume.
*This is actually a “cheat”, because physical semi-transparency has to be simulated by indirect light calculation or caustics, but for dense volumes like wax it’s very effective and the loss of realism is insignificant.



You can simulate the effect more accurately by rendering caustics,
In that case the Opaque attribute in the Arnold attributes of the object’s shape node must be checked and more steps must be taken allow refractive caustics to be ray-traced.

Note that simulating the effect using caustics will be very demanding in Transmission samples and Ray Depth.


Understanding Transparency Render Settings
Arnold Translucency
> Arnold Refractive Caustics

Using Arnold’s Ambient Occlusion node to create an eroding paint shader effect

Maya 2018 | Arnold 5

Arnold’s Ambient Occlusion (dirt) node can be used as a procedural mask to create interesting material effects like in this example of paint that is eroded at the model’s bulging areas to reveal metal beneath it.

In this shader’s case the Ambient Occlusion node is connected to the Mix property of an Arnold Mix shader, that blends between two different Arnold Standard Surface shaders, one simulating the underlying tin metal, and the other simulating the red paint that covers it.

Note that in the Ambient Occlusion node the Invert Normals property is checked, so that the effect will create a mask for the bulges and not for the creases,
And also that the Self Only property is checked so that the node will behave as a fixed object mask disregarding the proximity of other objects.
In this example the output of the Ambient Occlusion node is also process using a Remap Value node to increase it’s contrast so it will define borders between the areas.