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Kestrel Renderer

Kestrel is a CPU path tracer that reads scenes in a subset of the Mitsuba 0.6 XML format. It produces physically-based images via unidirectional path tracing with Multiple Importance Sampling (MIS) and Next Event Estimation (NEE).

Sponza with a glass sphere, rendered by Kestrel

The Sponza atrium with a dielectric sphere under a large area light, rendered with the path integrator.

Building

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)

The binary is placed at build/kestrel.

Running

kestrel <scene.xml> [-o <output>] [-i path|direct|direct_bsdf] [-s <spp>] [-t <threads>]
Flag Default Description
<scene.xml> (required) Path to the scene file in Mitsuba XML format.
-o <output> output.exr Output file path. The file extension selects the format.
-i <integrator> path Rendering algorithm. path = full global illumination with MIS; direct = single-bounce light sampling (NEE); direct_bsdf = single-bounce BSDF sampling. See Integrators.
-s, --spp <n> (scene) Override the scene's sampleCount.
-t, --threads <n> all cores Number of worker threads. Defaults to the hardware concurrency.

Example

./build/kestrel data/scenes/cbox/cbox.xml -o render.png
./build/kestrel data/scenes/veach_mi/mi.xml -o render.exr -i direct

Output formats

Extension Encoding Bit depth Notes
.png sRGB (gamma 2.2) 8-bit per channel Suitable for display.
.exr Linear float 32-bit per channel HDR; use for compositing or tone mapping.
.ppm sRGB (gamma 2.2) 8-bit per channel ASCII; uncompressed fallback.

Rendering settings

Samples per pixel and image resolution are specified inside the scene file (see sensors.md). The integrator, output path, sample-count override (-s), and thread count are the only runtime flags.

See the remaining reference pages for scene authoring: