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These guidelines are for users of the App SDK who want to use it to create a scene for rendering with V-Ray from the data in their host application scene. We will not discuss details on how to write code with the App SDK here - there are separate docs and examples for this included in the SDK package. Rather we will cover what V-Ray plugins to add to the scene, how to link them and what parameters to set.
Note: This document will be updated and extended over time. floatingpagetoc

1. Introduction

1.1. A note on terminology

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There is an example tiny scene in section 7. Its contents should become understandable by reading the following sections.

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The following are the types recognized in a V-Ray scene (think .vrscene file). They have corresponding types in the different AppSDK App SDK language bindings. The SDK uses the respective basic language types wherever possible and defines custom type classes for the rest.

• Basic types: int, bool, float, Color (3 float RGB), AColor (4 float ARGB), Vector (3 float), string (UTF-8), Matrix (3 Vectors), Transform (a Matrix and a Vector for translation).
• Objects: references to other plugin instances.
• Typed lists: The typed lists in App SDK are IntList, FloatList, ColorList, VectorList, TransformList and VectorList PluginList.
• Generic heterogeneous lists: The In C++, the App SDK uses a generic type class called Value for items in a generic list. In C#, Python and Node.js, native language types are used (lists or arrays). Note that generic lists can be nested.
• Output parameters
  : These are additional values generated by a given plugin which may be used as input by others. For example the TexAColorOp plugin  plugin (described in section 5.2) can be referenced directly as a texture, resulting in its default color texture output, but you can also refer to any of its other outputs, like sum, difference, maximum etc. for different results (Note: in some cases connecting an output parameter to an input parameter may not work directly, so you'd have to make the connection through a wrapper plugin like TexAColor or TexFloat).
  In App SDK output parameters are represented by the PluginRef type which combines a plugin reference and an output name.

Parameter polymorphism is an important feature of V-Ray. Texture parameters accept simple (basic) values, so instead of creating an additional texture plugin which generates a single color you just set a Color value to the texture slot. Same goes for float textures and single float values etc. You can also set the value of a texture parameter to an output parameter as described above.

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Apart from documentation included with the App SDK and this guide, the help pages for 3dsMax and Maya on docs.chaosgroupchaos.com are a good source of parameter information and examples, although they use the user-friendly UI names for things and not the actual scene parameter names.
A very useful tool for basic parameter information is plgparams.exe included in the binary folder of the SDK. It lists all parameters for the specified plugin (or all plugins with -list) and their types, default values and text comments. Similar information can be obtained using the ListAllPluginsAndProperties example in the C++ folder (or equivalent code for another language).
It is often useful to save out your scene to a file to inspect if you did everything properly. For example you may have failed to set some parameter properly and you will see this in the file as a missing or incorrect value, although you can also check the result of the set operation in your code. You can try to pinpoint problems by deleting parts of the scene (parameters or whole plugins) and re-rendering.
It can be very helpful if you have a V-Ray for 3dsMax or Maya and use it to export vrscene files to see what plugins and parameters are written out. The exporters for 3dsMax and Maya can be considered "ground truth" (even though they may have an occasional bug or missing feature).
If you're getting a black render make sure your camera is positioned and oriented properly and not inside an object. Keep in mind the default up-axis is Z, but it can be set to something else, usually Y. You might also get invisible or black objects if something is wrong with the attached material. In this case you can still the object in the alpha channel, especially if there is nothing behind it.
Another thing to watch out for is V-Ray's errors and warnings, so always implement the DumpMessage callback.

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Note: The reason the renderer uses the square of the parameter value is the property of the Monte Carlo integration method that to reduce noise (variance) by half (1/2 noise), you need four times as many samples (4x), to get 1/10 the variance you need 100x more samples... This way we get linear results from linear increases in the subdivs parameters.

2. Defining camera position

One of the first things you'd want to do is control your camera. This is done through the RenderView plugin. You will always want to create and setup this plugin, exactly one, in your scenes. (The exception is when you are baking textures - then you'd use BakeView.)

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• fov - The horizontal field of view in radians.
• orthographic - Enable to have orthographic projection instead of perspective (RenderView::fov doesn’t matter in this case, in favor of RenderView::orthographicWidth).
• transform - A transformation (rotation + translation) which defines where the camera is and how it is rotated. The matrix is in column-major format and you will need to calculate it yourself. You can't set rotation angles as in most 3D software. The default camera orientation with identity matrix is so that +Y is pointing up and -Z is the view direction. If your scene uses +Y for up-axis, you will need to set V-Ray's scene up-axis accordingly - see the Units subsection in the settings section below.

For advanced camera effects, such as DoF, exposure, distortion, vignetting, etc. you will need to enable the physical camera in addition to RenderView. See the Physical camera subsection in the settings section below for details. You can also use SettingsCameraDof instead, if you only need depth of field (see 6.11. Miscellaneous).

3. Creating lights

Good lighting is the most important thing for getting good photorealistic renders. It also affects image noise and performance. Some lights (generally the simpler ones, especially the first four in the list) render faster and with less noise than others. Things that may affect noise and performance of lights are: having a texture instead of flat color; having a complex mesh; being an area light with small relative size.

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• Node => Instancer2 => N * Node (invisible) -> GeomSomething
  
  and even
  
  
• Node => Instancer2 => Nodes => Instancer2 => etc.

5. Creating materials

Exporting materials is probably the most complicated part, because it may involve complex shader networks, especially in apps with high artistic control, such as the popular DCC tools from Autodesk. Nevertheless, you can get good results even by using only a few plugins.

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A general note on settings plugins: when you create a new Renderer object there are no instances of them, so you will need to create them before changing parameters. If you start rendering the AppSDK App SDK will create a SettingsOutput and if the render mode is RT it will create SettingsRTEngine. On the other hand, if you're loading a scene from file, it will have instances of most (but not all) settings plugins and you need to use them. This is because every time V-Ray exports a vrscene file it automatically writes out the settings even if they are at default values.

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These are controlled from the SettingsOutput plugin, but it is one of the few exceptions where you should not touch the plugin directly. The AppSDK App SDK has APIs for setting image and region size (i.e. renderer.setRenderRegion, depends on language).

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• FilterBox - All samples within a box with sides 2*size are taken with equal weight.
• FilterArea - All samples within a circle with radius size are taken with equal weight.
• FilterTriangle - Sample weight falls off as a triangular function of off-center distance.
• FilterGaussian - The classical blur filter.
• FilterSinc - Less blurry low-pass filter. See Wikipedia.
• FilterLanczos (currently default in V-Ray for 3dsMax and Maya) - See Wikipedia.
• FilterCatmullRom - A cubic edge-enhancing filter.
• FilterCookVariable
• FilterMitNet - Mitchell-Netravali cubic filter with subjectively optimized compromise of blurring and detail in the additional blur and ringing parameters which correspond to B and C from the original paper.

To apply a filter, just create an instance of one of those plugins. You can use only one at a time.

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The default values when you create a SettingsColorMapping plugin are different from the recommended values in 3dsMax and Maya for legacy reasons. These are the values you should use for new scenes:

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If you save the rendered image from the VFB and not from an AppSDK App SDK API, the corresponding Settings{JPEG|PNG|EXR|TIFF} plugin controls compression quality and bits per channel. You may need to change these according to your needs.

If you want to enable motion blur, set the SettingsMotionBlur plugin on parameter to 1. It also has the geom_samples parameter that affect quality, but may cost a lot of render time if increased. It should equal the number of geometry samples in the geometry data if it is non-static. Note that this plugin (SettingsMotionBlur) conflicts with CameraPhysical.

The SettingsLightLinker plugin allows you to define include or exclude lists for lights and objects, so that for example specific lights do not affect some objects etc. Refer to the plugin parameter metadata for explanations.

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If you are not using CameraPhysical for depth of field, you can use SettingsCameraDof instead. Note that this plugin (SettingsCameraDof) conflicts with CameraPhysical.

• on - Set on - Set to true to enable DoF.
• aperture - The size of the camera aperture in scene units. Note that increasing this number corresponds to decreasing the physical camera's F-number.
focal_dist - Distance from the camera to the focus plane in scene units
• .
• aperture - The size of the camera aperture in scene units. Note that increasing this number corresponds to decreasing the physical camera's F-number.
• focal_dist - Distance from the camera to the focus plane in scene units.

The .vrscene can store multiple cameras, where only one can be set as ‘renderable’ at a time. The rest of the cameras can be chosen for rendering, for example in V-Ray Standalone, by using the -camera command flag. This is useful, as oftentimes a project requires rendering different sequences from different cameras, while nothing else changes in the scene - a simple example would be to render two different views of the same visualization and in this way, the same scene can be rendered twice with V-Ray Standalone. An example scene with two cameras would have one them to render by default while the other will have dont_affect_settings flag raised.

In shading setups, textures can be projected from cameras. This can either be the same camera used for rendering, or another camera in the scene, used only for projecting a texture. In both cases, an extra SettingsCamera and RenderView plugin is exported for the camera projection with the dont_affect_settings flag raised. This is similar to the Multiple Cameras setup. In all cases, it’s a good idea to export one camera for rendering, and another one for the texture projection, even if it’s the same camera, as different properties apply for each.

7. Minimal renderable scene

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VRayClipper

Volumetric plugins

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The information from this page is also available at User Guide V-Ray Application SDK.