Cryptomatte: the rank planes are resolved once per evaluation and the GPU path reduces them on all cores, instead of formatting and looking up channel names for every pixel in a single-threaded loop (#473)

AuxChannels::crypto_rank_planes resolves a layer's (ID, coverage) planes once; crypto_ranks keeps its signature on top of it. The CPU effect and the GPU effect's aux image (effectcraft_effects::crypto_aux_image, rayon) index the planes per pixel. Output is bit-identical.

crates/gpu/src/fx_depth.rs

@@ -276,21 +276,9 @@ fn cryptomatte(e: &mut Enc, ctx: &EffectCtx, b: GBuf, a: &AuxChannels) -> Option
     let layer = layers.iter().find(|l| l.as_str() == want || l.ends_with(want)).unwrap_or(&layers[0]).clone();
     let manifest = a.manifests.iter().find(|(l, _)| *l == layer).map(|(_, m)| m.as_slice());
     let sel = effectcraft_effects::selection_hashes(pr.s("selection"), manifest);
-    // Per aux pixel: coverage-weighted ID colours (RGB) and the selection's coverage (A).
-    let n = (a.width * a.height) as usize;
-    let mut img = Image::new(a.width, a.height);
-    for (i, px) in img.data.iter_mut().enumerate().take(n) {
-        let ranks = a.crypto_ranks(&layer, i);
-        let m: f32 = ranks.iter().filter(|(id, c)| *c > 0.0 && sel.contains(&id.to_bits())).map(|(_, c)| *c).sum::<f32>().clamp(0.0, 1.0);
-        let mut c = [0.0f32; 3];
-        for (id, cov) in &ranks {
-            let k = effectcraft_effects::id_color(*id);
-            for j in 0..3 {
-                c[j] += k[j] * cov;
-            }
-        }
-        *px = [c[0], c[1], c[2], m];
-    }
+    // Per aux pixel: coverage-weighted ID colours (RGB) and the selection's coverage (A), on all
+    // cores with the rank planes resolved once.
+    let img = effectcraft_effects::crypto_aux_image(a, &layer, &sel);
     let tex = e.g.upload_image(&img)?;
     let plane = lookup(e, &b, a, &tex, [0.5, 0.5], [0.0; 4]);
     let mut p = op(7);