SoftBox

Soft shadow area light for Nuke 17 ScanlineRender2

By Marten Blumen

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ScanlineRender2's built-in lights only cast hard shadows: they send one shadow ray to the centre of the light. SoftBox adds an AreaLight node plus a ScanlineRender2 light shader, slrRectLight, that samples shadow rays across the whole light surface the way a path tracer does. The result is a smooth, physically based penumbra from a single light, and it is faster than faking one with a grid of lights.

Top: v1.1 grid of hard-shadow lights (the penumbra is built from stepped copies). Bottom: v1.2 stochastic sampling. 960x540, render times from ScanlineRender2 in Nuke 17.1.

Features

• Stochastic soft shadows (default) -- one USD RectLight, shadow rays jittered across its surface every sample
• No banding -- the penumbra is a true gradient that converges with more samples, instead of overlapping shadow copies
• Faster than a light grid -- 16 or 64 shadow rays cost less than 16 or 64 lights
• Works with ScanlineRender2's sampling -- at low Shadow Samples, the render's camera samples also clean up the shadow
• Grid mode kept for the v1.0/v1.1 look
• Full transform -- translate, rotate, scale via standard Axis_knob
• Viewport wireframe -- orange rectangle with direction arrow
• USD native -- writes a standard UsdLux RectLight (Grid mode: DiskLights)

Installation

From Release

1. Download SoftBox-v1.2-Nuke17-win64.zip from Releases
2. Unzip it into your .nuke folder so you get C:\Users\<you>\.nuke\SoftBox\
3. Add this line to ~/.nuke/init.py (create the file if needed):

   nuke.pluginAddPath('./SoftBox')

4. Restart Nuke 17.0 or 17.1 and find AreaLight under 3D > Lights

The plugin is tied to one Nuke minor version (the DDImage ABI changes between 17.0 and 17.1), so the zip carries a build for each, and SoftBox loads the one matching the running Nuke:

~/.nuke/
|-- init.py                  # nuke.pluginAddPath('./SoftBox')
`-- SoftBox/
    |-- init.py              # adds the <major.minor>/ folder matching the running Nuke
    |-- menu.py              # 3D > Lights > AreaLight
    |-- README.txt
    |-- LICENSE
    |-- 17.0/AreaLight.dll, slrRectLight.dll
    `-- 17.1/AreaLight.dll, slrRectLight.dll

Upgrading from v1.0? Delete the old ~/.nuke/AreaLight.dll and the AreaLight lines in ~/.nuke/menu.py. A DLL loose in ~/.nuke/ is loaded by every Nuke version.

Build From Source

Requires the Visual Studio 2019 toolset (v142, the toolchain Foundry builds Nuke 14.1-17.1 with) and CMake 3.20+. Point NUKE_DIR at the Nuke you are building for; the install subfolder is taken from that NDK's version.

git clone https://github.com/bratgot/SoftBox.git
cd SoftBox

# Nuke 17.1
cmake -S . -B build --preset vs2019 -DNUKE_DIR="C:/Program Files/Nuke17.1v1"
cmake --build build --config Release
cmake --install build --config Release

# Nuke 17.0 (separate build directory)
cmake -S . -B build-17.0 -G "Visual Studio 16 2019" -A x64 -DNUKE_DIR="C:/Program Files/Nuke17.0v4"
cmake --build build-17.0 --config Release
cmake --install build-17.0 --config Release

The DLLs are built to build/plugin/Release/ (AreaLight.dll and slrRectLight.dll). cmake --install installs to ~/.nuke by default (override with --prefix) and adds the registration block to ~/.nuke/init.py only if it is not already there.

If a build directory was configured before this layout existed, reconfigure it with cmake --fresh ... so the install prefix is reset.

Packaging a Release

After building every Nuke version you want to ship:

cmake -P cmake/package.cmake

This stages dist/SoftBox-v<version>/SoftBox/ from every build*/ directory and zips it as dist/SoftBox-v<version>-Nuke17-win64.zip, ready for GitHub Releases or Nukepedia. The version comes from project(... VERSION ...) in CMakeLists.txt. dist/ is git-ignored.

Usage

1. Create an AreaLight node and connect it to your scene
2. Set Width and Height for the light surface size -- this sets how soft the shadows are
3. Adjust Intensity, Exposure, and Color
4. On the Shadow tab, leave Shadow Mode on Stochastic and set Shadow Samples for smoothness:

Shadow Samples	Result	Use Case
1	Noisy; relies on ScanlineRender2 camera samples	Look-dev with high camera samples
16	Smooth with light grain	Previews
64	Clean	Final renders, close-ups

5. Connect to ScanlineRender2 and render

How It Works

Nuke 17's ScanlineRender2 is a ray tracer, and its light shaders are plugins loaded by name: a USD light's light:shaderId of DiskLight loads slrDiskLight.dll, and so on. Nuke ships shaders for Disk, Sphere, Distant and Dome lights, all of which send a single shadow ray to the light's centre, which is why their shadows are hard. There is no shader for USD's RectLight.

SoftBox supplies one. In Stochastic mode the AreaLight node writes a RectLight prim, and slrRectLight.dll handles it. For each shading point it picks jittered points across the rectangle from ScanlineRender2's per-sample random number generator, traces a shadow ray to each, and weights them by the emitter cosine and inverse-square distance. Every camera sample picks new points, so the penumbra averages into a smooth gradient, exactly as a path tracer renders an area light.

Grid mode keeps the v1.0 method: N DiskLights spread over the rectangle, each with intensity / N. Their overlapping hard shadows fake the penumbra, and render time grows with every light.

Either way, shadow softness comes from the light's size (Width x Height); Shadow Samples only controls how smooth the gradient is.

Tips

• Shadow softness = light size. Bigger light = wider penumbra
• Shadow Samples = smoothness. More samples = less grain
• Scripts from v1.0/v1.1 open in Stochastic mode; set Shadow Mode to Grid to get the old look back. The two modes differ slightly in brightness.
• The shader's .dll must sit next to AreaLight.dll; the SoftBox folder layout takes care of that

Project Structure

SoftBox/
├── UsdAreaLightOp.cpp    # AreaLight node
├── UsdAreaLightOp.h      # Plugin header
├── slrRectLight.cpp      # ScanlineRender2 stochastic RectLight shader
├── CMakeLists.txt        # Build configuration
├── CMakePresets.json     # VS2019 / VS2022 presets
├── cmake/
│   ├── install_user_init.cmake  # one-time ~/.nuke/init.py registration
│   └── package.cmake     # builds the dist/ zip for release
├── dist_readme.txt       # README.txt shipped inside the zip
├── docs/                 # README images
├── test/                 # soft_shadow_test.nk + benchmark.py
├── init.py               # adds the build matching the running Nuke
├── menu.py               # 3D > Lights toolbar entry
├── LICENSE               # MIT license
└── README.md             # This file

Requirements

• Nuke 17.0 or 17.1
• Windows x64
• ScanlineRender2

License

MIT -- see LICENSE for details.