iris/tests/allocation_cost.rs

use iris::{harness::Harness, prelude::*};
use std::{
    alloc::{GlobalAlloc, Layout, System},
    cell::Cell,
};

struct Counting;
thread_local! {
    static COUNT: Cell<Option<usize>> = const { Cell::new(None) };
}
fn count() {
    COUNT.with(|count| {
        if let Some(n) = count.get() {
            count.set(Some(n + 1));
        }
    });
}
// The wrapper preserves System's allocation and deallocation contracts;
// observing calls here also counts allocations hidden inside layout helpers.
unsafe impl GlobalAlloc for Counting {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        count();
        unsafe { System.alloc(layout) }
    }
    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        unsafe { System.dealloc(ptr, layout) }
    }
    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, size: usize) -> *mut u8 {
        count();
        unsafe { System.realloc(ptr, layout, size) }
    }
}
#[global_allocator]
static ALLOCATOR: Counting = Counting;

#[test]
fn unchanged_tree_reuses_layout_storage() {
    for rule in [
        SizeRule::FREE,
        leftover(1).clamp(20, 80).into(),
        SizeRule::clamp(20.into(), 80.into()),
    ] {
        let mut h = Harness::new((600, 200));
        let mut children: Vec<StrongWidget> = Vec::new();
        for _ in 0..8 {
            let a = rect(Color::RED).add(&mut h.rsc);
            h.rsc.widgets_mut().set_size_rule(a, Axis::X, rule.clone());
            let row = (a, rect(Color::BLUE))
                .span(Dir::RIGHT)
                .add_strong(&mut h.rsc);
            children.push(row);
        }
        let root = h.rsc.widgets_mut().add_strong(Span {
            children,
            dir: Dir::DOWN,
            gap: Px::ZERO,
        });
        h.state.root = Some(root);
        h.frame();
        let ids: Vec<_> = h.render.active.keys().copied().collect();
        for frame in 0..8 {
            for &id in &ids {
                h.rsc.widgets_mut().mark_for_redraw(id);
            }
            h.resize((600 + frame % 2, 200));
            h.frame();
        }
        COUNT.set(Some(0));
        for frame in 0..100 {
            for &id in &ids {
                h.rsc.widgets_mut().mark_for_redraw(id);
            }
            h.resize((600 + frame % 2, 200));
            h.frame();
        }
        let allocations = COUNT.replace(None).unwrap();
        println!("rule={rule:?}: {allocations} allocations over 100 resize frames");
        assert_eq!(allocations, 0);
    }
}

/// A text drawn again at the width it already has places no glyphs and shapes
/// nothing, so the frame costs nothing at all -- which is what the shaping
/// cache is for, and a copy of the attrs made to ask it undid for any text
/// naming its font family.
///
/// Only that case: a text drawn at a width it has not seen places its glyphs,
/// and placing them allocates a list to hold them.
#[test]
fn redrawing_a_text_at_one_width_allocates_nothing() {
    let mut h = Harness::new((600, 200));
    let mut col = Span::empty(Dir::DOWN);
    let mut texts = Vec::new();
    for _ in 0..8 {
        let text =
            wtext("wrapping shapes one source into as many lines as the box leaves room for")
                .size(16)
                // Named rather than generic, because a named one is the family
                // that costs an allocation to copy.
                .family(Family::Named("sans-serif".into()))
                .wrap(true)
                .add_strong(&mut h.rsc);
        texts.push(text.id());
        col.push(text);
    }
    let root = col.add(&mut h.rsc);
    h.set_root(root);
    let redraw = |h: &mut Harness| {
        for &id in &texts {
            h.rsc.widgets_mut().mark_for_redraw(id);
        }
        h.frame();
    };
    for _ in 0..8 {
        redraw(&mut h);
    }
    COUNT.set(Some(0));
    for _ in 0..100 {
        redraw(&mut h);
    }
    let allocations = COUNT.replace(None).unwrap();
    println!("text: {allocations} allocations over 100 redraws of 8 texts");
    assert_eq!(allocations, 0);
}