UntoldViewer: a comparison bench for the engine against RealityKit on Vision Pro

[miogds]

A new demo: the engine's comparison bench on Apple Vision Pro. The same objects (a dartboard and four darts to start), each with an engine model and a USDZ twin made from the same source, shown at the same spot in your room by the Untold Engine or by RealityKit, one tap apart, so sharpness, aliasing, lighting and frame time compare like for like while the engine is pushed. It is the bench behind untoldengine/UntoldEngine#1359 (foveation, temporal anti-aliasing, the forward path, RealityKit's look).

What it has

• A window: the catalog, the placement (in front of you, or fixed in the room), the motion (still, or a 24-second debug tour identical in both renderers), the engine's anti-aliasing, render quality, lighting, render path and the temporal filter's knobs, and a diagnostics line with the GPU time per frame and what the object adds to the empty space.
• A measurement pass (Tools/measure.sh) that places the object, records and summarises a run, and a calibration panel built from code in both renderers to read colour and tone pixel by pixel.
• UntoldViewer/README.md covers running it, adding an object (a folder and a USDZ), the tour, the measurements and the known differences between the renderers.

The engine's frame time

The tour's pose is taken at the instant the compositor predicts the frame will be shown, through the engine's setupCallbacks(frameUpdate:handleInput:), so a moving object steps by the display's period from frame to frame instead of by the varying lag of the update behind the presentation, which read as judder; the run summary counts the skipped refreshes and the presentation revisions for the check on the device. That needs the engine's frame-time change, miolabs/UntoldEngine#73 (feature/presentation_time_animation, six commits on top of #1359's branch), to be retargeted to develop once #1359 merges.

Building

The project is generated from project.yml (xcodegen generate) and, while the engine work is in review, points at a local engine checkout (../../xr_foveation/UntoldEngine) on feature/xr_headset_rendering with feature/presentation_time_animation on top; once both land, the package switches to the engine's URL on develop, as the comment in project.yml says. The models and the USDZ twins are LFS objects; Config/Local.xcconfig holds the developer's team and bundle prefix and is ignored.