Coalesce resize layout diagnostics

tests/generated.rs

@@ -18,6 +18,33 @@ use iris::random::{Edits, Lens, Rng, SpanEdit, Tree, grow};
 
 const DEPTH: usize = 4;
 const SEEDS: [u64; 6] = [1, 2, 3, 5, 8, 13];
+const REGION_ULPS: u32 = 4;
+
+fn ordered_bits(value: f32) -> u32 {
+    const SIGN: u32 = 1 << 31;
+    let bits = value.to_bits();
+    match bits & SIGN {
+        0 => bits | SIGN,
+        _ => !bits,
+    }
+}
+
+fn same_coordinate(got: f32, want: f32) -> bool {
+    got == want || ordered_bits(got).abs_diff(ordered_bits(want)) <= REGION_ULPS
+}
+
+fn same_region(got: Option<PixelRegion>, want: Option<PixelRegion>) -> bool {
+    match (got, want) {
+        (Some(got), Some(want)) => {
+            same_coordinate(got.top_left.x, want.top_left.x)
+                && same_coordinate(got.top_left.y, want.top_left.y)
+                && same_coordinate(got.bot_right.x, want.bot_right.x)
+                && same_coordinate(got.bot_right.y, want.bot_right.y)
+        }
+        (None, None) => true,
+        _ => false,
+    }
+}
 
 fn plant(h: &mut Harness, seed: u64, edits: &Edits) -> Tree {
     let (root, tree) = grow(&mut h.rsc, seed, DEPTH, edits);
@@ -138,7 +165,10 @@ fn assert_same(seed: u64, what: &str, warm: (&Harness, &Tree), cold: (&Harness,
     for (i, (&w, &c)) in wt.ids.iter().zip(&ct.ids).enumerate() {
         let (got, want) = (wh.region(&w), ch.region(&c));
         drawn += usize::from(got.is_some());
-        if got == want {
+        // Equivalent composition orders can differ by a few f32 ULPs. Bound
+        // that representation drift directly, while whether a widget drew
+        // remains exact.
+        if same_region(got, want) {
             continue;
         }
         wrong += 1;