iris/tests/cases/determinism.rs

//! 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 = UiSpan::new(Len::ZERO, cut).shifted_desc();
        let measured = painter
            .widget_at(&self.probe, top.axis(Axis::Y))
            .len(Axis::X);
        let px = painter.to_px(measured.apply_leftover(), Axis::X);

        let below = UiSpan::new(cut, painter.region_len(Axis::Y)).shifted_desc();
        let place = below.axis(Axis::Y);
        match px > Px::from_f32(self.threshold) {
            true => painter.widget_at(&self.wide, place),
            false => painter.widget_at(&self.narrow, 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"
        );
    }
}