VLR:

VLRはNVIDIA OptiX 7を使用したGPUモンテカルロレイトレーシングレンダラーです。
VLR is a GPU Monte Carlo ray tracing renderer using NVIDIA OptiX 7.

特徴 / Features

GPU Renderer using NVIDIA OptiX 7
Full Spectral Rendering (Monte Carlo Spectral Sampling)
(For RGB resources, RGB->Spectrum conversion is performed using Meng-Simon's method [Meng2015])
RGB Rendering (built by default)
BSDFs
- Ideal Diffuse (Lambert) BRDF
- Ideal Specular BRDF/BSDF
- Microfacet (GGX) BRDF/BSDF
- Fresnel-blended Lambertian BSDF
- UE4- or Frostbite-like BRDF [Karis2013, Lagarde2014]
  Parameters can be specified using UE4 style (base color, roughness/metallic) or old style (diffuse, specular, glossiness).
- Mixed BSDF
Shader Node System
Bump Mapping (Normal Map / Height Map)
Alpha Texture
Light Source Types
- Area (Polygonal) Light
- Point Light
- Image Based Environmental Light
Camera Types
- Perspective Camera with Depth of Field (thin-lens model)
- Environment (Equirectangular) Camera
Geometry Instancing
Light Transport Algorithms
- Path Tracing [Kajiya1986] with MIS
- Light Tracing
- Light Vertex Cache Bidirectional Path Tracing (LVC-BPT) [Davidovič2014]
Correct handling of non-symmetric scattering due to shading normals [Veach1997]

構成要素 / Components

libVLR - Renderer Library based on OptiX
CのAPIを定義しています。
Exposes C API.
vlrcpp.h - Single file wrapper for C++
std::shared_ptrを用いてオブジェクトの寿命管理を自動化しています。
Automatically manages lifetime of objects via std::shared_ptr.
HostProgram - A program to demonstrate how to use VLR

API

Code Example using VLRCpp (C++ wrapper)

using namespace vlr;

ContextRef context = Context::create(cuContext, enableLogging, maxCallableDepth);

// Construct a scene by defining meshes and materials.

SceneRef scene = context->createScene();

TriangleMeshSurfaceNodeRef mesh = context->createTriangleMeshSurfaceNode("My Mesh 1");
{
    Vertex vertices[] = {
        Vertex{ Point3D(-1.5f,  0.0f, -1.5f), Normal3D(0,  1, 0), Vector3D(1,  0,  0), TexCoord2D(0.0f, 5.0f) },
        // ...
    };
    // ...
    mesh->setVertices(vertices, lengthof(vertices));

    {
        Image2DRef imgAlbedo = loadImage2D(context, "checkerboard.png", "Reflectance", "Rec709(D65) sRGB Gamma");
        Image2DRef imgNormalAlpha = loadImage2D(context, "normal_alpha.png", "NA", "Rec709(D65)");

        ShaderNodeRef nodeAlbedo = context->createShaderNode("Image2DTexture");
        nodeAlbedo->set("image", imgAlbedo);
        nodeAlbedo->set("min filter", "Nearest");
        nodeAlbedo->set("mag filter", "Nearest");

        ShaderNodeRef nodeNormalAlpha = context->createShaderNode("Image2DTexture");
        nodeNormalAlpha->set("image", imgNormalAlpha);

        // You can flexibly define a material by connecting shader nodes.
        SurfaceMaterialRef mat = context->createSurfaceMaterial("Matte");
        mat->set("albedo", nodeAlbedo->getPlug(VLRShaderNodePlugType_Spectrum, 0));

        ShaderNodeRef nodeTangent = context->createShaderNode("Tangent");
        nodeTangent->set("tangent type", "Radial Y");

        uint32_t matGroup[] = { 0, 1, 2, 0, 2, 3 };
        mesh->addMaterialGroup(matGroup, lengthof(matGroup), mat, 
                               nodeNormalAlpha->getPlug(VLRShaderNodePlugType_Normal3D, 0), // normal map
                               nodeTangent->getPlug(VLRShaderNodePlugType_Vector3D, 0), // tangent
                               nodeNormalAlpha->getPlug(VLRShaderNodePlugType_Alpha, 0)); // alpha map
    }

    // ...
}

// You can construct a scene graph with transforms
InternalNodeRef transformNode = context->createInternalNode("trf A");
transformNode->setTransform(context->createStaticTransform(scale(2.0f)));
transformNode->addChild(mesh);
scene->addChild(transformNode);

// Setup a camera
CameraRef camera = context->createCamera("Perspective");
camera->set("position", Point3D(0, 1.5f, 6.0f));
camera->set("aspect", (float)renderTargetSizeX / renderTargetSizeY);
camera->set("sensitivity", 1.0f);
camera->set("fovy", 40 * M_PI / 180);
camera->set("lens radius", 0.0f);

// Setup the output buffer (OpenGL buffer can also be attached)
context->bindOutputBuffer(1024, 1024, 0);

// Let's render the scene!
context->setScene(scene);
context->render(cuStream, camera, enableDenoiser, 1, firstFrame, &numAccumFrames);

TODO

Make the rendering properly asynchronous.
Python Binding
Simple Scene Editor
Compile shader node at runtime using NVRTC to remove overhead of callable programs.

動作環境 / Confirmed Environment

現状以下の環境で動作を確認しています。
I've confirmed that the program runs correctly on the following environment.

Windows 10 (21H2) & Visual Studio 2022 (17.2.4)
Core i9-9900K, 32GB, RTX 3080 10GB
NVIDIA Driver 516.40 (Note that versions around 510-512 had several OptiX issues.)

動作させるにあたっては以下のライブラリが必要です。
It requires the following libraries.

libVLR
- CUDA 11.6
- OptiX 7.4.0 (requires Maxwell or later generation NVIDIA GPU)
Host Program
- OpenEXR 3.1
- assimp 5.0

注意 / Note

モデルデータやテクスチャーを読み込むシーンファイルがありますが、それらアセットはリポジトリには含まれていません。
There are some scene files loading model data and textures, but those assets are NOT included in this repository.

参考文献 / References

[Davidovič2014] "Progressive Light Transport Simulation on the GPU: Survey and Improvements"
[Kajiya1986] "THE RENDERING EQUATION"
[Karis2013] "Real Shading in Unreal Engine 4"
[Lagarde2014] "Moving Frostbite to Physically Based Rendering 3.0"
[Meng2015] "Physically Meaningful Rendering using Tristimulus Colours"
[Veach1997] "ROBUST MONTE CARLO METHODS FOR LIGHT TRANSPORT SIMULATION"

ギャラリー / Gallery

A variant of the famous Cornell box scene. The left box has anisotropic BRDF with circular tangents along its local Y axis (roughness is smoother along tangent, rougher along bitangent).

An object with UE4- or Frostbite 3.0-like BRDF (Textures are exported from Substance Painter) illuminated by an area light and an environmental light.

Model: Substance Painter
IBL image: sIBL Archive

Caustics generated from Stanford bunny model illuminated by directional area light.
The renderer uses spectral rendering for this.