writer library

The encoder: .4dgs files written from gaussian state.

A separate library rather than part of package:fourdgs/fourdgs.dart, for the same reason package:fourdgs/io.dart is one — except that here the cost of merging them is not tidiness but a build that does not happen at all.

The chunk orderer spreads coordinates into a Morton code, and the masks that do it are 64-bit values: 0x1249249249249249 and two of its neighbours. On the web a Dart int IS a JavaScript number, so those literals are past 2^53 and the compiler rejects them where they are written — not where they are used. A read-only consumer that never encodes anything still could not compile, because the umbrella library exported this one and an export is enough to put a file in the compile graph.

That is exactly what happened: mission_control, a Flutter web app that only ever reads .4dgs, could not be built at all while it depended on version 0.1.0 of this package.

The masks are not the bug and must not be "fixed". The values genuinely exceed 2^53; a JavaScript number cannot hold them however they are spelled. Computing them at runtime — shifting two 32-bit halves together, int.parse, anything — makes the compiler stop complaining and makes the codes silently wrong on the web, which trades a build failure for corrupt output. The encoder is correct where a Dart int is a real 64-bit integer, which is every native target and wasm, and it is honest about not being available where one is not.

flutter build web --wasm does not avoid this either: Flutter still emits a dart2js fallback bundle for browsers without wasm, so the JavaScript compile runs regardless of what the app targets.

So: import this library to write, and expect it to be unavailable on the web. Import package:fourdgs/fourdgs.dart to read, anywhere.

Classes

FourdgsKeyframeDeltaOptions

Cadence, mode, and everything else a keyframe-delta file needs.

FourdgsSample

One population, at one instant, with identity.

FourdgsWriteOptions

How a scene is written. The defaults are the reference encoders' own.

Constants

fourdgsShLadders → const Map<String, List<int>>

Named per-band ladders, band 1 first, as website/docs/reference/compression.md measures them.

fourdgsShMaxBits → const int

fourdgsShMinBits → const int

The narrowest and widest a spherical-harmonic band may declare (spec §6.5).

Functions

fourdgsQuantizeSh(int value, int bits) → int

Round one coefficient byte onto the grid bits names, at bin centres.

fourdgsShBound(int bits) → int

The maximum deviation, in code units, a bit depth guarantees.

fourdgsShStep(int bits) → int

The grid pitch, in code units, that a bit depth implies.

writeFourdgsBytes(FourdgsGaussianSet gaussians, double durationSec, {FourdgsWriteOptions options = const FourdgsWriteOptions()}) → Uint8List

Encode gaussians as one in-memory .4dgs file.

writeFourdgsToSink(Sink<List<int>> sink, FourdgsGaussianSet gaussians, double durationSec, {FourdgsWriteOptions options = const FourdgsWriteOptions()}) → void

Encode gaussians to sink, one complete framed record at a time.

writeKeyframeDeltaBytes(List<FourdgsSample> samples, double durationSec, {FourdgsKeyframeDeltaOptions options = const FourdgsKeyframeDeltaOptions()}) → Uint8List

Encode samples as a complete keyframe-delta file.

writeKeyframeDeltaToSink(Sink<List<int>> sink, List<FourdgsSample> samples, double durationSec, {FourdgsKeyframeDeltaOptions options = const FourdgsKeyframeDeltaOptions(verify: false)}) → void

Encode samples to sink, one complete framed record at a time.

Exceptions / Errors

FourdgsInvalidInput

The caller handed the encoder something no conforming file can be written from.