Render a still with the path tracer

pfx render --scene traces a shot on the GPU with pfx’s path tracer, denoises it, and writes a 16-bit master and an 8-bit delivery PNG with a JSON manifest beside them. It runs headless. This page renders the engine’s neutral sample shot from a checkout of this repository.

pfx’s path tracer on its neutral sample shot: a grey disc and a grey ring turning back and forth over a dark floor, in soft key, fill and rim light

Find the shot

A product keeps its recipes in a folder: its look in presets/<product>.toml and its shots in shots/<product>.toml. The engine’s own tests use a neutral product, sample, in crates/assets/tests/recipes:

$ pfx list --scenes --product sample --recipes crates/assets/tests/recipes
sample  shapes  The sample icons in a row, turning

Render it

$ pfx render --scene shapes --product sample --still --recipes crates/assets/tests/recipes --size 1920x1080
tmp/renders/sample/still/sample-still-shapes-1920x1080.png

The command prints the delivery’s path. Output lands under the caller’s git tree, in tmp/renders/<product>/still/:

sample-still-shapes-1920x1080.png          the 8-bit sRGB delivery, 1.6 MB
sample-still-shapes-1920x1080.master.png   the 16-bit sRGB master, 6.1 MB
sample-still-shapes-1920x1080.json         the manifest

Every pixel samples adaptively to a noise threshold of 0.01, and the frame then goes through the denoiser (The denoiser). The manifest records the device, the recipes it read with their sha256, the sampling and what the tracer did. On an AMD Radeon RX 9060 XT this shot’s 1920×1080 frame took 1.35 s of GPU time:

"tracer": {
  "gpu_ms": 1353.0,
  "mean_samples": 56.2,
  "most_samples": 64,
  "sampling": { "cap": 64, "denoise": true, "growth": 1.5, "min": 16, "threshold": 0.01 },
  "triangles": 8836,
  "version": "1.0.0"
}

Change the frame

--draft stops sooner (threshold 0.05, at most 16 samples), denoised too, for quick looks; --samples N sets the cap.
--size 3840x2160 renders at 4K.
--angle front|three-quarter|top, --turn, --tilt and --zoom move the camera; --background transparent|#rrggbb|hdri and --shadow on|off change the setting.
--clip renders the shot’s keys as a 60 fps clip instead, encoded with the system’s ffmpeg.

The asset renderer’s recipes, masters and outputs are in crates/assets/README.md, and the pfx tool’s commands are listed in The crates. When pgpu, a GPU queue, is on PATH the render waits its turn there; without it the render runs directly.

In a game’s own code

The same tracer is a library: a game or app stages a scene with pfx_trace::stage::scene and traces it with pfx_trace (Tracer cameras and staging), and pfx bake uses it for the light the live renderer shows (Probe baking).