Files
iris/tests/cases/determinism.rs
T
iris-ai 0954770ceb Say what a child gets of a container's box in that box's own lengths
Three things the measurements asked for, all about how much a box that came
from an answer costs.

**A part in the box's own coordinates.** Saying "less eleven pixels at the
end" in frame lengths from the box's start means reading how long the box is,
and a container whose box is its own answer then depends on its own answer:
`Pad` drew sixty-four times in one resize frame at seed 13, chasing its own
width. `Part::Of` says the same thing as a part of the box, which composes
without a length -- pixels are pixels wherever the box lands -- and what a
child under it holds for maps back through that part onto the container's
own box rather than onto the frame.

**One axis of the box at a time.** `extent_len` pinned both axes, so a span
dividing one of them held for one length of the other as well, and a resize
broke every span whose cross-axis answer moved.

**No lazy placement.** Leaving a child's answer to be placed at the end of
the parent's draw, rather than as the child answers, was meant to save a
recomposition. It costs one instead: the drawing is put in the part first
and in the answer's box after, and where it does not hold for both that is
two drawings rather than one. Seed 1 at depth 8 went from 391 widget draws
on a resize to 29 with it gone. The test that pinned three draws for a
numeric leaf in a span goes with it.

Seed 1 at depth 8, widget draws / distinct widgets / update, against #18's
head and against the commit this branch started from:

| phase   | e44dea3      | 34cafb6      | here          |
| ---     | ---          | ---          | ---           |
| cold    | 369/261/10.6 | 463/274/13.3 | 516/288/12.0  |
| repaint | 1            | 1            | 1             |
| many    | 157/95/0.33  | 263/108/0.59 | 187/119/0.52  |
| size    | 16/12/0.018  | 3/3          | 3/3/0.010     |
| scroll  | 2/0.002      | 1            | 1/0.004       |
| resize  | 13/13/0.019  | 22/15/0.032  | 24/76/0.090   |

Seed 13 at depth 8 is where the protocol still costs: `many` 1091 draws
against #18's 524, and `resize` 2215 against a frame #18 does not draw at
all. Both are the same shape -- an answer measured in one box and drawn in
another -- and the handoff says where that comes from.

Checked: fmt, clippy with -D warnings, 108 suite tests, 20 core tests, the
11 generated cases, and the shrinker at 400 trees of depth 5, which fails
seeds 2 (repaint) and 108 (reorder).
2026-09-18 01:06:05 -04:00

104 lines
3.9 KiB
Rust

//! A measurement that decides control flow.
//!
//! Comparing boxes catches a widget that moved. It does not catch a widget
//! that measured a child, believed a different answer from the one a cold
//! start would give, and took the other branch -- which is the same defect
//! arriving somewhere it cannot be ignored. A widget here branches on what it
//! measured, so a disagreement shows up as a different tree.
use iris::harness::Harness;
use iris::prelude::*;
/// Measures `probe` across `axis` and draws one of two children on the
/// answer. Its own configuration never changes, so which child is drawn is a
/// property of the layout alone.
struct BranchesOnMeasurement {
probe: StrongWidget,
wide: StrongWidget,
narrow: StrongWidget,
threshold: f32,
}
impl Widget for BranchesOnMeasurement {
fn draw(&mut self, painter: &mut Painter) -> Size {
let cut = Len::from_parts(Rel::ZERO, Px::from_int(40));
let top = Place::Within(Part::From(UiSpan::new(Len::ZERO, cut)));
let measured = painter
.widget_at(&self.probe, UiRegion::FULL, [Place::Within(Part::All), top])
.len(Axis::X);
let px = measured.apply_leftover().to_px(painter.px_len(Axis::X));
let below = Place::Within(Part::From(UiSpan::new(cut, painter.extent_len(Axis::Y))));
let place = [Place::Within(Part::All), below];
match px > Px::from_f32(self.threshold) {
true => painter.widget_at(&self.wide, UiRegion::FULL, place),
false => painter.widget_at(&self.narrow, UiRegion::FULL, place),
};
Size::LEFTOVER
}
}
fn plant(h: &mut Harness, threshold: f32) -> (WidgetId, WidgetId) {
let words = "the quick brown fox jumps over the lazy dog and keeps running";
let probe = wtext(words).size(16).wrap(true).add(&mut h.rsc);
let wide = rect(Color::RED).add(&mut h.rsc);
let narrow = rect(Color::BLUE).add(&mut h.rsc);
let branch = BranchesOnMeasurement {
probe: probe.add_strong(&mut h.rsc),
wide: wide.add_strong(&mut h.rsc),
narrow: narrow.add_strong(&mut h.rsc),
threshold,
}
.add(&mut h.rsc);
let side = rect(Color::GREEN).width(120).add(&mut h.rsc);
h.set_root((side, branch).span(Dir::RIGHT));
(wide.id(), narrow.id())
}
/// Which of the two branches drew, as a pair a test can compare.
fn taken(h: &Harness, wide: WidgetId, narrow: WidgetId) -> (bool, bool) {
(h.region(&wide).is_some(), h.region(&narrow).is_some())
}
#[test]
fn a_branch_taken_on_a_measurement_holds_across_repaints() {
for threshold in [0.0, 200.0, 400.0, 600.0, 779.0, 780.0, 781.0, 2000.0] {
let mut h = Harness::new((900, 600));
let (wide, narrow) = plant(&mut h, threshold);
let first = taken(&h, wide, narrow);
assert_ne!(first, (false, false), "threshold {threshold}: neither drew");
for frame in 0..4 {
h.rsc.widgets_mut().get_dyn_mut(wide);
h.rsc.widgets_mut().get_dyn_mut(narrow);
h.frame();
assert_eq!(
taken(&h, wide, narrow),
first,
"threshold {threshold}, repaint {frame}: the branch moved when nothing did"
);
}
}
}
#[test]
fn a_branch_taken_on_a_measurement_is_the_one_a_cold_start_takes() {
for threshold in [0.0, 200.0, 400.0, 600.0, 779.0, 780.0, 781.0, 2000.0] {
let mut warm = Harness::new((900, 600));
let (wide, narrow) = plant(&mut warm, threshold);
warm.resize((640, 480));
warm.frame();
warm.rsc.widgets_mut().get_dyn_mut(wide);
warm.frame();
let mut cold = Harness::new((640, 480));
let (cwide, cnarrow) = plant(&mut cold, threshold);
assert_eq!(
taken(&warm, wide, narrow),
taken(&cold, cwide, cnarrow),
"threshold {threshold}: warm and cold took different branches"
);
}
}