ai-app/IRIS_TODO.md

iris: known problems and things still to build

Iris's own list for the library, recorded 2026-09-04 in her words where it matters, so the agents working through RUST.md pick these up in a sensible order rather than rediscovering them. Each item says where it sits in the order and what "done" looks like. Tick and date them in place.

Fix

• Input does not fall through by input type (2026-09-04). SensorUi::run_sensors (src/default/sense.rs) used to set "consumed, stop checking lower layers" from mere hover — a widget registered for nothing but click() blocked a Scroll meant for whatever was behind it, since "the cursor is over this widget" and "this widget handled the event" were the same check. Fixed by judging consumption per input kind: with no button transition and no scroll happening this frame ("momentary" activity), the topmost hovered widget still wins, same as before; when something momentary is happening, only a widget whose registered senses actually include a matching non-hover one (checked via a new TypeEventManager::registered, which lists what a widget registered without running anything) consumes it, so a widget with only Hovering/click handlers can no longer block a scroll from reaching a list underneath. iris/src/sense_tests.rs builds a button-over-a-list Stack with a plain HasEvents impl (no GPU or window) and checks both directions: a scroll over the button reaches the list, and a real click still reaches the button — confirmed to fail on the pre-fix code and pass after.

• Appending one image to an already-loaded list rebuilds every other image's bind group (2026-09-05, fixed 2026-09-05). Found by the benchmark below: GpuTextures::update (core/src/render/texture.rs) triggered rebuild_image_bind_groups — a loop over every live standalone image, rebuilding its BindGroup — whenever the shared masks or move_offsets GPU buffer was resized (masks_resized || moves_resized in UiRenderNode::update, core/src/render/mod.rs), and a widget getting its first move-offset slot (LAYOUT.md section 2 — every widget gets one on first draw) could be exactly what grows that buffer. So one new message with one new image, appended to a transcript that already has N images loaded, did not cost O(1): it cost one create_image for the new image plus one make_image_bind_group per existing image, because the new widget's own move slot pushed the arena past its capacity. Measured directly in iris/examples/bench_images.rs: appending a 1,001st image to 1,000 already-settled ones reported 1,001 bind-group creates for that one frame, not 1 (./run-bench.sh images, frame 5 in the transcript below).

  Fix: masks/move_offsets never belonged in a standalone image's own bind group (group 2) in the first place — the group also holds that image's own texture view, which is the only thing that is genuinely per-image, so a buffer shared by everything forced a rebuild of every group the moment it moved. Gave masks/move_offsets their own bind group (group 3 in shader.wgsl and UiRenderNode: masks_layout/ masks_group), bound once per frame in UiRenderNode::draw rather than once per draw call, instead of duplicating them into every per-image group. GpuTextures and its image bind groups now know nothing about either buffer — rebuild_image_bind_groups is called only from grow_array (the atlas array texture growing, which genuinely does change what every image's own bind group must reference) — so a masks/move_offsets resize now touches exactly one bind group, ever, regardless of how many images are live. Numbers after the fix, same benchmark and command:

  ./run-bench.sh images
  frame=1 bind_group_creates=1000   (cold load, unchanged)
  frame=2 bind_group_creates=0      (was 1000 -- see the item below)
  frame=3 bind_group_creates=0
  frame=4 bind_group_creates=0
  (append one image here)
  frame=5 bind_group_creates=1      (was 1001)
  frame=6 bind_group_creates=0
  

  run-headless.sh tabs --shot still 27266 bytes, byte-for-byte unchanged, confirming the bind-group restructuring changed nothing about what is drawn.

• Bind-group creation takes two frames to reach the steady state, not one (2026-09-05, closed by the fix above, 2026-09-05). Same benchmark: loading 1,000 images cold used to report 1,000 creates on frame 1 (expected — create_image, one per new image) and again 1,000 on frame 2, before settling to 0 from frame 3. This was rebuild_image_bind_groups firing a second time for the same masks/move-offsets buffer-growth reason as the item above, confirming the guess recorded here — the two were exactly the same root cause measured two different ways. Frame 2 now reports 0 (see the numbers above); not a separate fix.

Build

• Benchmarks, not unit tests, run on demand (2026-09-05; a benches/ or a script under iris/, never in cargo test). The scenario that matters most is a message list — chat apps and this app's transcript alike — stressed with many messages and many images. One case in particular: resizing an input box (typing enough text to grow it) that pushes a long list of messages above it must stay very fast and recalculate almost nothing — a move of everything above, not a re-layout. That is exactly the O(1) move chain in LAYOUT.md; the benchmark is what proves it. Done when the numbers are in this file with the command, and the input-box case reports draws re-run, not just frame time.

  Built as two rigs, chosen per scenario by whether a real wgpu device is needed (UiRenderState/Widgets touch no GPU or window, so most of this runs as an ordinary binary — the same property layout_tests.rs relies on):

  • iris/benches/message_list.rs — a plain Instant-timed binary ([[bench]] harness = false in iris/Cargo.toml), not criterion: see the file's own header for why (short version — every scenario here reduces to a count UiRenderState::take_counters already produces, which criterion's statistical machinery adds nothing to and which a new dependency is not worth pulling in for). Covers (a) first-frame cost of a message list of N wrapped-text rows (one in 20 also carrying a small in-memory image) for N = 100/1,000/10,000; (b) per-frame cost of scrolling that list, 200 ticks; (c) the input-box case — a fixed-height field at the bottom of the screen growing by a line 40 times, with the message list above it filling the rest of the screen. Run: cd iris && cargo bench --bench message_list (always release — cargo bench builds the bench profile, which is optimized).
  • iris/examples/bench_images.rs — needs a real device, so it runs through iris/run-headless.sh bench_images, printing UiRenderNode::take_image_bind_group_creates() (a new counter, added in core/src/render/texture.rs and core/src/render/mod.rs, mirroring UiRenderState::take_counters) each frame. Covers (d): 1,000 image rows, checked both cold (does bind-group creation reach zero once loaded) and after appending one more image once settled (does that stay cheap) — the second question is what actually matters for a live transcript and is what turned up the two Fix items above.
  • iris/run-bench.sh [list|images] runs either or both and is what to run before/after touching Scroll, Span, Sized, the move-offset chain, or GpuTextures.

  Numbers (2026-09-05, release, cargo bench/run-headless.sh, this VM: AMD Ryzen 7 3800X, 8 cores, rustc 1.98.0 nightly-2026-09-03):

  cd iris && cargo bench --bench message_list
  (a) first frame, N=100:    30.30ms  draws=227   rewrites=15   moves=0
  (a) first frame, N=1000:  186.04ms  draws=2252  rewrites=150  moves=0
  (a) first frame, N=10000:1770.36ms  draws=22502 rewrites=1500 moves=0
  (b) scroll, N=100/1000/10000, 200 ticks each:
      draws=200 rewrites=0 moves=200 (identical at every N)
      per-tick average: 0.0002ms (identical at every N)
  (c) input grows 40 lines, N=100/1000/10000 rows above it:
      draws=320 rewrites=40 moves=160 (identical at every N)
      per-line average: 0.0012-0.0013ms (identical at every N)
  
  cd iris && ./run-bench.sh images        (2026-09-05, before the fix)
  frame=1 bind_group_creates=1000   (cold load)
  frame=2 bind_group_creates=1000   (see Fix item above)
  frame=3 bind_group_creates=0
  frame=4 bind_group_creates=0
  (append one image here)
  frame=5 bind_group_creates=1001   (see Fix item above)
  frame=6 bind_group_creates=0
  
  cd iris && ./run-bench.sh images        (2026-09-05, after the fix)
  frame=1 bind_group_creates=1000   (cold load, unchanged -- genuine work)
  frame=2 bind_group_creates=0
  frame=3 bind_group_creates=0
  frame=4 bind_group_creates=0
  (append one image here)
  frame=5 bind_group_creates=1      (one image's own create_image, O(1))
  frame=6 bind_group_creates=0
  

  Reading it: (a) is real, necessary work — shaping and laying out N never-before-seen text rows — and scales with N as it must, ~10x cost per 10x N. (b) and (c) are the pass conditions that matter: both are exactly flat across N = 100 to 10,000, confirming LAYOUT.md's O(1) move chain holds for both scrolling and for a growing input box pushing the message list — draws/moves per tick or per line do not grow with list size, and the per-operation cost (a fraction of a microsecond) is nowhere near a frame budget. (d)'s cold-load and steady-state halves behave as designed; its append half did not, until the fix above moved masks/move_offsets out of the per-image bind group — now flat at O(1) the same way (b) and (c) are.

• Masks defined relative to each other. Wanted: mask A multiplies by something and also applies mask B — a mask can reference a parent mask, the way the move chain references a parent offset. Today masks are independent regions. Design it beside the move chain (same shape: a parent index and a bounded walk in the shader); do it when a real widget needs it, not before.

• Positions as a single float per scroll. Iris raised, and half rejected, letting a scroll update one float rather than positions: input handling cares about most elements in a list, so absolute positions must be computed on the CPU anyway. LAYOUT.md's design already lands here (GPU walks the chain, CPU resolves on demand for hit tests). Keep the CPU resolution lazy and per query; do not materialise every row's absolute position per frame.

• Animations, last. Cosmetic, so after everything above. Must be modular — a piece of the library rather than a core part forced into everything, the same way input is. Whatever the mechanism, a widget that does not animate must pay nothing and import nothing for it.

Reconsider

• WidgetView. Iris is unsure of it: what she wants is an easy way to compose a widget from others (a button is the main case). With sizing folded into draw, composing may be easy enough that View is redundant. Decide after the layout change lands, by writing a button both ways and keeping the one that is shorter to explain; delete the other rather than keeping two ways.