A box in pixels was composed back up the move chain, on a grid fine enough
that the walk rounded once, while a widget's offer was threaded down through
its ancestors' offers. Two routes to one length, which is what
`Holds::through` allowed for -- and the offer's route broke at a region node.
`offered_region` fell back to `UiRegion::FULL` there, and `redraw` resolved
that against the node's slot entry, which holds the box its parent *placed*
the node in. Under a `Scroll` that is as long as the content rather than the
viewport, so everything below was re-asked at a width its own answer had
produced and the old answer confirmed itself: shrinker seed 220 on `reorder`
left a widget 290px out.
`ActiveData` now keeps a widget's box as lengths of its parent's box --
`given_len`, and `offer_len` for the box it was first asked about -- and
`DrawInfo` carries the pixel lengths, threaded down one `Len::to_px` at a
time: the box its parent gave it, then the part of that box its own answer
placed the drawing in, which `placed_lens` states once for both `placed_box`
and the walk. `Painter::px_size` and `px_len` read that value, and
`UiRenderState::asked_px` takes the same steps back up the parent chain where
a local redraw starts part-way down the tree. Neither chain has a coordinate
frame in it, so neither can break at a region node, and warm and cold reach
every length by the same expression.
Three things follow. `Holds::through` is the exact preimage of
`px + floor(rel * box)` -- two divisions, no allowance, the whole of a box
mapping back to itself. A local redraw asks in the box its parent gave it and
only where that box is as long as the offer, which retires `redraw`'s third
ask and the region-node exception beside it; `draw_inner` places the answer
inside that box itself. And symbolic regions are left to the GPU, hit testing
and remaps, where `Moves::resolve` is the only walk: `wide.rs`,
`Moves::compose`, `Moves::size_of`, `px_of`, `px_region`, `offered_region`
and `slot_wide` are gone, 252 lines of `core/` net.
`px` is deliberately not stored beside those lengths. A resize every widget's
`Holds` admits redraws nothing, so a stored pixel length would be stale on
every widget in the tree with nothing on it to say so, and refreshing it costs
a walk down every reused subtree on the resize path.
Instructions:u, medians of 21 runs, seed 1 at depth 8:
| phase | before | after | |
| --- | ---: | ---: | ---: |
| `cold`, 200 frames | 313.1M | 312.9M | -0.04% |
| `resize` | 408.1M | 405.6M | -0.61% |
| `many` | 1,924M | 1,756M | -8.75% |
| `scroll` | 357.3M | 323.4M | -9.49% |
| `repaint` | 363.3M | 315.4M | -13.18% |
`cold` and `resize` have all twenty-five work counters identical, so those
two rows say the draw path costs the same threaded as composed. The other
three do less work: `repaint` goes from 23 draw requests and 13 widget draws
a frame to 1 and 1, `scroll` from 20 and 11 to 8 and 2, `many` from 273 and
186 to 207 and 157. Primitive writes are unmoved in every phase.
Verified: `view`, `minimal`, `random`, `tabs` and `text` render
byte-identical at 1920x1200 against `5b78002`, as does the `tabs` touch
replay before and after the gesture, and a live resize of `random` to
1280x800 is identical both to the old head's and to a cold render at that
size. The oracle passes 100 seeds in release and 120 in debug -- the debug
run is the one that exercises the `Holds` assertion -- and the fifteen
shrinker cases pass at 400 seeds of depth 5 and 1000 of depth 6. Seed 220 is
`unsettled::a_widget_under_a_region_node_is_asked_in_the_box_that_node_was_offered`,
which needs both halves of this to fail: the old chain with the old allowance
passes it, and the old chain with the exact preimage does not.
`AGREE_STEPS` stays 2. One step passes the 100-seed oracle and fails the
400-seed shrinker on `resize-size` by 0.002 px, so what is left there is the
resize path re-expressing a part as a fraction of a box that changed length,
not a length reached two ways.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A widget reports a fraction of the box it was given. Span added that
fraction straight into a cursor that counts fractions of the row, and Pad
summed its padding onto it, both right only while the offer had the
parent's whole extent -- which a span's does not after a relative child.
DrawResult::size and known_len now compose the answer through the offer's
length, so a container reads lengths of its own box.
That exposed placed_box scaling a fractional answer against a box the
parent had already chosen from it, halving a nested span twice. The
near-edge alignment override becomes per-axis `decided` flags: a box the
parent chose from the answer is the answer, and is not placed again.
Span decides the row axis; Scroll and Stack's sizing child decide both.
Alignment is always the widget's own property now.
The window is no longer a move entry. Chains bottom out in MoveIdx::NONE
and the window is applied where a fraction becomes pixels, in to_px on the
CPU and by the uniform in the shader, which now snaps the summed coordinate
since a floor does not distribute over a sum. A resize rewrites no entry.
Verified: view, minimal, random, tabs and text render byte-identical at
1920x1200 against 5f16617, a live resize to 1280x800 is identical to a
cold render, and the 100-seed oracle, all fifteen shrinker cases at 400
seeds of depth 5, and 1000 seeds of depth 6 pass.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
`UiScalar` was `Len` without the `leftover` weight, which is the separation
canonical `main` already had as `Len` beside `LayoutLen` and this branch
collapsed. It is needed back for the queued clamp: a cap may not contain a
share, because a cap has to read the report a rule otherwise makes moot, and
a share puts the container's division into the same equation -- two
self-consistent assignments, which is the multiple-fixed-point failure
generated seed 13 punished for orthogonal sizing. `min(report, cap)` is not
a `LayoutLen` either: it is a sum of parts, and the smaller of two of them
is not one.
So `UiScalar` is `Len`, what was `Len` is `LayoutLen`, and the two say in
their docs which is which: a `Len` is pixels plus a fraction of a box -- a
position being the length from the box's start, which is why a span is two
of them -- and a `LayoutLen` is a `Len` plus a claim only a container
dividing its room can answer. `From<Len> for LayoutLen` is the one-way step
between them.
Names only; the shader's `UiScalar` is renamed with them. Checked: fmt,
clippy, 105 tests, and `tabs`, `minimal`, `view`, `text` and `random`
byte-identical at 1920x1200.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
`Px` and `PxVec2` reach the last places a pixel was a float: the window, the
box a widget reads, the box it is compared against, and `PixelRegion`. A
pointer, a wheel notch and a shaped glyph advance still arrive as floats,
and each is put on the grid where it arrives.
`Holds` is an interval of `Px`. `HOLDS_EPSILON_PX` is gone with the
`exact`/tolerant split it existed for: `at` is the length a widget read, an
open end is the next step along, and `same_px` is equality. `Span`'s margin
from `5ed9e87` goes too -- the box a parent hands back and the sum of what
its children asked for are counts of the same step, so the boundary decides
the same way from either side.
Three things had to be true for that, and were not:
`Holds::through` inverts `px + rel * box`, which rounds -- so a part of a
given length came from a range of boxes, and inverting the length alone gave
a point that need not contain the box the part was drawn in. It now maps the
half step either side, and one more for a length composed down the chain
against the same length measured against the window.
`RegionRemap` translates when a box only moved, rather than dividing to find
each part's fraction and multiplying to place it again. Two roundings landed
a step from where growing the tree that way does; a move is exact on a grid,
which is the whole reason `tests/drift.rs` was written.
A pixel is `1/1024` rather than `1/64`. At `1/64` the residue of a length
reached two ways was one step, and one step was 0.016 px -- enough to move
a box. `PX_SHIFT` and `REL_SHIFT` are the only statement of the grid now,
and the shader's copy is prepended from them rather than written twice.
Checked: fmt, clippy, 102 tests, 100 generated seeds in 75 s, all five
shrinker cases at 300 seeds, and `tabs`, `view`, `minimal`, `text` and
`random` byte-identical at 1920x1200.
What the fuzzers ask for is now a step, not a twentieth of a pixel: the
shrinker's five cases agree within one (`resize` exactly), and the oracle's
two-operation cases within two. The residue is a single rounding either way
-- it scales with the grid rather than accumulating, which is why it is a
thousandth of a pixel now. Closing it means one way of asking how long a box
is, rather than a chain composed down and a length measured against the
window; that is a bigger change than this one.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
SetSize took its declared length out of UiRegion::FULL, which is the box
it was already given, so a span that had sized that box from the same
hint had the fraction taken twice: .width(rel(0.5)) in a 400-wide span
drew its child 100 wide. It held under a Pad or the root, which do not
honour a hint, and hid under px, where 200 of a 200-wide box is all of
it. The text example was 111,923 pixels from upstream/main because of
it.
Whoever draws a widget now takes its declared length, in its own box,
which is what a fraction of one means, and is the identity for a caller
that already reserved the space. rest is not taken: a share of what is
left over is only a length to the widget dividing one, so it passes up
in the size as it does out of a span. SetSize keeps only what it
declares.
A declared length is then part of the box its parent decided, so
changing one has to redraw the parent; the lengths resolved into a box
are kept beside it and compared. Assuming instead that any dirty widget
which declares a length needs its parent costs 17% of a frame that
dirties 130 of 260 widgets, and buys nothing.
All five reference renders, the resize render and the image replay are
byte-identical to upstream/main, the 100-seed sweep passes, and the
resize fixture is 1.286 ms against 1.289 before.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A local redraw drew a dirty widget in the box it was placed in. When a reader
decided that box from the widget's own answer -- an aligned span sized to its
children, a text at the tail of a row, a scroll's content -- the old answer is a
fixed point of measuring there whatever the content now says, so the layout had
two stable answers and which one it reached depended on the tree's history.
`tests/unsettled.rs` has the two shrunk cases: the four-widget aligned span,
and a scroll placing a pass-through `SetSize` in a box the content decided,
where the span under it was placed once and nothing at its own edge said so.
`ActiveData::offered_px` keeps the pixel size of the box the parent first asked
about the child in, whether through `known_len` or a first `place`, beside `px`,
the box it drew against. A dirty widget whose size reads an axis on which some
reader up its chain gave what it read a box other than the one it asked in is
not drawn locally: the chain is marked and the parent of the highest such
placement draws, since above it every box is a constraint rather than an
answer. The walk goes up the whole reader chain because a pass-through hands a
derived box down unchanged.
`Scroll` read its box's length for the clamp through `px_len`, which records
the reported size as depending on it, and it does not: its size is its
content's. That made every scroll tick a size question asked in a derived box,
at 34x the instructions. `Painter::px_len_for_draw` is the read that records
nothing. Instructions per frame on the depth-8 rig against the previous head:
`many` at 32 dirty 0.66M to 0.74M, at 130 dirty 27.7M to 26.5M, `resize` 15.8M
to 15.0M, `scroll`, `repaint` and `size` unchanged. The shrinking fuzzer passes
200 trees at depth 7 in all four cases, the hundred-seed sweep passes, and the
five reference renders and the resize render are byte-identical.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
A resize had its own mechanism: `reads_output` recorded that a widget had
looked at the output, `update` scanned every active widget for one whose
`output_px` had moved, marked it and its whole reader chain, and
`resize_marks` kept those marks from counting as content dirtiness --
while `on_resize` answered the same question for every other box. Two
answers to "does this drawing survive its box changing length", and the
one that applied to the window ignored what the widget had declared.
With the output held as the root of the chain there is one question. A
resize offers the root widget its box again, `try_reuse` answers per axis
from `on_resize`, and `redraws_under` prices the subtree. Gone with it:
`reads_output`, `resized`, `resize_marks`, the scan, the eager reader
marking, and the shallowest-first branch in `redraw_updates`, which only
existed because resize marking worked differently -- the settle loop now
has one order.
Two things this needed. An unslotted widget may be reused when only its
parent's box changed length: it has nothing of its own to write, and what
it drew is a fraction of that box, so the slot above it already carries
the change. And `root_readers` holds the widgets whose size came from the
output rather than their own box -- `MaxSize` -- since no box of theirs
need have changed; they are marked per axis, from a set kept as they draw
rather than by scanning.
`a_resize_does_not_redraw_what_the_shader_can_move` now says `Scale`,
which is what it was always describing, and `a_resize_redraws_what_does
_not_scale` is its other half. `ReadsWidth` declares `Scale` across the
axis it does not read, so per-axis precision comes from the widget rather
than from which output axis it happened to touch.
Resize phase, seed 1 depth 8: 6.45M instructions per frame to 5.84M.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Choosing which dirty widget to settle next asked every one of them how
deep it was, and answering meant walking its ancestry to the root. At
130 of 260 widgets dirty that was 25.8% of the frame -- more than laying
out or rendering.
A widget's depth is known where it is drawn: its parent's plus one. So
`Painter` carries it and `ActiveData` keeps it, and the choice reads a
field. Being reused counts as being visited, so the two reuse paths keep
it current too; only a subtree nothing looked at can hold an old one,
and nothing under an unvisited subtree is being ordered.
The order is unchanged, so nothing about the layout is: the five
reference renders and the resize render are byte-identical. What the
carried depth might get wrong is itself, so `depth` asserts it against
the ancestry in debug builds, and the hundred-seed sweep passes with
those assertions on -- including the reshuffles, which are what move a
widget to another parent.
Same load, 1000 frames, 130 of 260 dirty: 8.16M instructions per frame
to 7.14M, median 0.813 ms to 0.639, and the choosing from 25.8% of the
frame to 4.7%. What is left of it is iterating the dirty set itself,
which a `HashSet` walks by capacity rather than by length.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Two holes the random trees found, both of which kept a wrapping text shaped
for a width it no longer had.
**A region is a fraction of a slot's box, so an unchanged region is not an
unchanged box.** `try_reuse` compared regions, and a child drawn at
`UiRegion::FULL` of a slot whose box had just halved compared equal to
itself and was reused without being descended into. `ActiveData` now keeps
the pixel size of the box it drew against and the comparison is against
that, which is the question that was being asked all along and is right
through a slot change and an output resize alike.
**A size the parent learnt by drawing the child is an answer for that box
only.** The walk looking for what cannot survive a length change skipped a
child whose own box was a fixed width -- correctly, its box does not change
-- but that width was what the child reported when the span drew it in the
span's box, and the span's box did change. So a child whose size the widget
read is redrawn unless it declares an exact `size_hint` for the changed
axis, which is the one case the parent did not have to draw it to know.
The cost is that a size-reading container gives up its reuse when its box
changes length, which is every span, so `OnResize::Scale` now earns its
keep on moves and on subtrees whose sizes nobody read rather than on every
stretch. Correct first; `replace_cost` still measures the case the chain was
built for.
`tests/generated.rs` is what found both and what says they are fixed: 90 of
90 warm trees now land where a cold build does, against 83 before this
commit and 83 on `db1751f`. The ignored sweep agrees over 300 checks on 100
seeds.
`a_fixed_length_child_is_not_redrawn_when_the_box_around_it_grows` became
`a_declared_length_...`: the child now says its width, since a width the
span measured is not one it may keep.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
A widget's region is now held in the coordinates of the slot it draws in
rather than the window's, and `Painter::place` is how a container asks for a
slot: it draws a child it decides the box of and may decide again. Everything
under that slot is a fraction of its box, so placing the child a second time
is one entry to write whether it moved or changed length. A child drawn any
other way has no slot and shares its nearest ancestor's.
That is what keeps the chain short. `chain_cost` measured depth as the cost
-- free to 8, +42.6% at 16 -- and a slot per widget put a transcript's glyphs
past that for nothing, since almost every slot was zero. `Span`, `Aligned`
and `Scroll` are the containers that re-place a child after drawing it, and
`tests/layout.rs` pins that four widgets between a span and a leaf leave the
leaf's chain one deep.
`UiRegion::stretch`, `UiRegion::stretchable` and `UiScalar::stretch` are
gone. Nothing is inverted any more: a box that changed length is written to
its slot, and the descendants recompose against it in the shader. That also
retires the case the guard existed for, where a fixed length has no fraction
to recover -- `tests/layout.rs` now stretches a 40-tall row on its other
axis, which `stretchable` refused outright.
What still walks the CPU is deciding who must draw again, which no chain can
answer: `mark_resized` descends from the widget whose box changed and marks
anything whose own box changed length and whose drawing reads it. A part of
a box with no relative extent on an axis is a fixed length, and composing
into it leaves none either, so the walk stops where a length did not change
-- an 80-wide child in a widened row is not redrawn though it says `Redraw`.
`Span`, `Pad`, `Stack`, `Offset`, `Aligned`, `SetSize` and `LayerOffset` say
`Scale`: each places in fractions and offsets of its own box and none reads
the box's pixel length. `Scroll` and `MaxSize` do read pixels and stay
`Redraw`.
45 tests pass, five of them new. Render verification comes after the CPU
side, per the owner.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The plumbing for O(1) subtree movement (LAYOUT.md §2), with every slot
still at zero, so this changes no pixels and the next commit can change
behaviour against a known-good picture.
Every active widget owns a slot in `UiData::moves`: a translation in
physical pixels and the slot it is relative to. A primitive instance and
a mask each name one, and `prelude.wgsl` walks the chain and adds the
accumulated delta. A mask resolves its own chain rather than the drawn
primitive's, so a stationary viewport can clip content that moves inside
it. `CHAIN_LIMIT` is stated on both sides; it bounds a malformed cycle
rather than any real tree.
A slot outlives any one `ActiveData`, because a redraw replaces that
while the widget's children go on pointing at the slot, so it lives in
`UiRenderState::moves` keyed by widget and is retired when the widget
stops being drawn. `MoveIdx` is its own type rather than another
`Id<u32>`: it sits beside `MaskIdx` in an instance and the two must not
be swappable.
`Vec2` is now `repr(align(8))`, which is WGSL's alignment for a
`vec2<f32>`, so a GPU struct holding one is laid out the way its shader
reads it without saying so itself -- `GlyphPrimitive` no longer states
its own alignment, and `MoveOffset` never has to. Both keep a manual
`unsafe impl Pod`, since the trailing padding that alignment introduces
is what `derive(Pod)` refuses. `WindowUniform` holds the `Vec2` its
shader has always called `dim` rather than two loose floats, which was
the last place the two sides described the same bytes differently.
Checked: fmt, clippy and 40 tests. `tabs` (with the image replay),
`view` and `minimal` render byte-identical to `upstream/main`, and
`text` is unchanged.
iris-aiandClaude Opus 5
iris