After solve.fluid the results view had nothing to draw: a fluid step's
fields are per cell, the view only knew nodal fields, and the deformed
display it built dropped the geometry surfaces, so even the part
vanished.
A fluid step now has its own display (`engine::flow`, on render's
flow display data), shared by the headless pictures and the window:
the part drawn as it is, its faces coloured by the field in the fluid
beside them, the field on a slice through the domain and streamlines
seeded on the inlet face upstream of the obstacles, coloured by speed
when the legend shows velocity. It is first shown with velocity
magnitude on a slice through the middle, normal to the horizontal axis
across the flow.
New commands: results.slice {step, field: velocity|pressure, axis:
x|y|z|none, position, frame}, results.surface {step, show} and
results.streamlines {step, show, count, max_steps, seeds | line,
frame}, which replies with what it traced. results.contour takes
velocity and pressure for fluid steps (a new `pressure` field) with
the usual bands and legend clamp, and results.frame walks a fluid
step's frames. Streamlines leave the coming-soon list. Hostile
parameters are refused, and the counts are capped.
Part of #193.
A fluid step's result is a field per cell of a regular grid, not per
node, so the contour machinery had nothing to draw it with and the
viewport showed nothing after a fluid solve.
Add `render::flow`, CPU display data for such fields with no solver
dependency (render stays at L1): an axis-aligned slice through the
cells as triangles carrying cell-centred values (interpolated between
the two layers either side, outer centres moved to the domain faces,
cells inside obstacles left out), the field sampled at a surface
beside the fluid cells for colouring an obstacle, and streamlines
traced through the trilinear velocity field by the midpoint rule,
seeded on a lattice upstream of the obstacles. Seeds, steps and the
total number of points are capped so hostile counts cost a bounded
time. `contour::banded` fans band pieces into scene triangles for the
callers.
Part of #193.
Every cell did an atomicMax on the same word; a workgroup reduction first
leaves one per 256 cells. Same result, less contention on a single
address.
Part of #529.
The CPU stays the default, so every existing result and fixture is
bit-identical; "gpu" steps on the device FIELDCRAFT_GPU picks through the
registered backend, and is an error when the build has none. The desktop
app and the CLI (hence the MCP server) register fieldcraft-lbm-gpu at
start; the summary names what stepped. Hostile values are errors.
Part of #529.
A new L7 crate: the CPU scheme's collision (TRT with Guo forcing), the
per-link streaming rules (bounce-back with Ladd's term, slip reflection,
open placeholders), the Zou–He boundaries and the momentum exchange per
force group as wgpu compute shaders, stepping the flow fieldcraft_lbm's
Flow prepared, through its Backend trait: populations stay on the device,
a chunk of steps is one submission, and only frames, forces and the
stability check come back. Populations are stored as deviations from
their weights, which keeps single precision honest: the verification
cases (Poiseuille with Λ = 3/16, Couette with wall forces, Taylor–Green,
a sphere's drag, a Zou–He channel) agree with the CPU to 2–5e-6 in
velocity, 1e-6 in density and 5e-5 in force, with those tolerances stated
in the tests. The rules are applied one thread per link rather than in a
per-cell loop, which lavapipe's JIT miscompiles (and which diverges on
real GPUs anyway). Native only for now; the browser registers nothing.
Part of #529.
run() drives a Backend in chunks of steps (to the next frame, history sample
or progress check) instead of the CPU Flow directly, so a device backend
registered by an application can step the same prepared flow: Flow keeps
building the grid, links and open cells and exposes them read-only, and
implements the trait itself. solve_fluid_on picks the CPU or the registered
device backend; solve_fluid stays the CPU and is unchanged in its results.
Part of #529.
Christian Svensson