Reaction-diffusion · mimo-v2.6-pro

Let me build a Gray-Scott simulation in index.html. Use Canvas 2D with typed arrays, ImageData for rendering. Grid size maybe 256x256, multiple steps per frame.

Let me write the file.

Design:
- Full page layout: canvas centered, control panel with sliders (feed, kill, Du, Dv, brush size, steps per frame), Pause/Resume, Reset buttons, maybe FPS display, preset buttons.
- Simulation: Float32Array u, v; laplacian with wrapping (9-point or 5-point). Use standard Gray-Scott with Du=0.16, Dv=0.08, dt=1.0, dx=1.0.
- Wrapping: precompute index arrays or use modulo arithmetic with fast paths. For N=256, per step 65536 cells * few ops — fine, run 8 steps/frame → 524k cell updates per frame, fine in JS.

Rendering: map V to color gradient. Use ImageData of size N×N and drawImage scaled onto display canvas with imageSmoothingEnabled = false... Actually smooth scaling might look nicer; keep off for crispness? Let's use smoothing on for organic look. Hmm, "Map concentrations to contrasting colors so evolving organic patterns are visible." I'll do a gradient: background dark navy/black for low V, then teal→yellow→white for high V. Maybe use both U and V: color from V primarily with U influencing.

Implementation details:
- u, v arrays; next arrays u2, v2.
- laplacian: use 3x3 kernel with weights: center -1, orthogonal 0.2, diagonal 0.05 (standard Gray-Scott "9-point"). With Du=0.16 that's stable with dt=1.
- Actually classic Karl Sims uses center -1, adjacent 0.2, diagonals 0.05. Fine.

Wrapping: precompute xm1, xp1, ym1, yp1 arrays for indices.

Steps: run `stepsPerFrame` iterations.

Pointer interaction: mouse/touch down and drag; brush radius adds V=0.5... Actually set v = min(1, v + amount) and u = max(0, u - amount). Use radius maybe 8 cells.

Verification plan with browser tool: run index.html, screenshot at t0, sample canvas pixels (via console eval? browser tool has inspect). I can use browser "inspect" to run JS? The browser tool: actions reload, inspect, screenshot, motion, click, drag, key, type, scroll. Inspect probably returns DOM/console info. To verify numerically I could expose a global `window.__sim` with sampling function and read console output... but I can only see console output if inspect shows it. Let me use console.log at intervals? Better: use `browser` with action "type"/"click" to interact and "screenshot" to see.

Plan checks:
1. Screenshot initial scene (seed blob at center).
2. Wait / motion frames to see evolution.
3. Click/drag elsewhere → screenshot showing new spot.
4. Click Pause → screenshot twice, compare (patterns frozen) — can compare screenshots visually.
5. Reset → screenshot shows initial seed restored.

To be more rigorous I can add a debug hook `window.__simStats()` returning e.g. sum of v and center value, and use inspect to read it — if inspect returns JS eval results. Unclear; I'll try. I'll expose `window.sim` object with fields and functions; then run `browser` inspect maybe with text? The browser tool params: x, y, toX, toY, text, delta. "inspect" likely prints DOM/console. Maybe text arg used for click/type. I'll just try and see.

Let me also add a stats readout in the UI (sum of V, max V) which I can verify via screenshots... hard. Instead maybe use inspect to see DOM text.

Let's write the code.

HTML structure:
- header title
- canvas (in a container)
- controls: buttons Pause/Resume, Reset, presets (Mitosis, Solitons, Coral, Maze?), sliders for feed/kill/steps/brush, checkbox for color scheme? Keep it moderate.

Careful: required params Du=0.16, Dv=0.08, feed=0.035, kill=0.062 defaults. Feed/kill sliders can adjust but default to those.

Grid: fixed N = 256 (square). Bound work per frame: stepsPerFrame default 8, slider 1–20.

Rendering: canvas display size = min(container width, viewport height) square, e.g. 720px. Use offscreen canvas of N×N with ImageData, then drawImage scaled.

Colors: for t = v (clamped), use gradient stops:
- 0.0: #0b1020 (deep)
- 0.15: #16324f
- 0.3: #1f8a8a (teal)
- 0.5: #7fd44c? Let's craft: dark blue → teal → green → yellow → warm white.

Also modulate by u maybe: use t = v*2.5 clamp 1? V values typically range 0 to ~0.4. Use t = clamp(v/0.4). Good.

Precompute a 256-entry LUT for colors, index = (v*255/0.4)|0 clamped.

Interaction mapping: pointer position relative to canvas → cell coords via scale factor N/rect.width.

Also keyboard: space toggles pause, R resets.

Let me write the JS.

```js
const N = 256;
const size = N*N;
let u = new Float32Array(size), v = new Float32Array(size), u2, v2;
let Du=0.16, Dv=0.08, feed=0.035, kill=0.062, dt=1.0;

function idx(x,y){ return y*N+x; }
// wrap tables
const xm = new Int32Array(N), xp = new Int32Array(N);
for (let i=0;i<N;i++){ xm[i] = (i-1+N)%N; xp[i] = (i+1)%N; }
```

step():
```js
function step(){
  for (let y=0;y<N;y++){
    const ym = xm[y]*N, y0 = y*N, yp = xp[y]*N;
    for (let x=0;x<N;x++){
      const xl = xm[x], xr = xp[x];
      const i = y0 + x;
      const uc = u[i], vc = v[i];
      const lapU = 0.2*(u[y0+xl]+u[y0+xr]+u[ym+x]+u[yp+x]) + 0.05*(u[ym+xl]+u[ym+xr]+u[yp+xl]+u[yp+xr]) - uc;
      const lapV = ...;
      const uvv = uc*vc*vc;
      u2[i] = uc + (Du*lapU - uvv + feed*(1-uc))*dt;
      v2[i] = vc + (Dv*lapV + uvv - (feed+kill)*vc)*dt;
    }
  }
  swap
}
```

Good.

Reset: fill u=1, v=0, seed center square region (e.g. N*0.1 side ~ 20x20) with v=1 (or 0.5), u=0.5 (reduced). Use a rounded blob: for dx,dy in -r..r where dist<r: v=1, u=0.5? Classic: u=0.5, v=0.25 in center square. Let's do square of side ~16 with u=0.5, v=0.25 and slight noise for organic. Actually "small central region with V and reduced U" — square region side = 16 px centered.

Add slight randomness? Reset should restore deterministic initial fields to compare — so keep deterministic (no random noise). Good for verification "compare the restored central seed with the initial scene".

Brush: radius default 10 cells; add: 
```js
for dy in -r..r, dx in -r..r: if dx*dx+dy*dy <= r*r: v[i] = Math.min(1, v[i] + 0.5*fall); u[i] = Math.max(0, u[i] - 0.5*fall);
```
with fall = 1 - dist/r maybe.

Rendering each frame: fill ImageData.

FPS counter and step counter displayed.

Now the UI: panel on the right or below. Keep responsive: flex column, canvas max size 640-760.

Let me write the file now.

Also add `window.__sim` debug API: `{ stats(): {vSum, uSum, maxV, centerV}, stepN, paused, reset() }` for verification. And maybe a function to get grid values.

I'll write it.

For verification in browser: initial screenshot, then use motion to see evolution, drag in an empty area, screenshot, click pause button, screenshot twice to compare, reset, screenshot.

To verify numerically I'd like console output. Perhaps `browser` "inspect" shows console logs. I could have the app log to console once at start and every ~2s? That might clutter. I'll expose stats in DOM: "steps: N, ΣV: x". Then inspect DOM text.

Let me write.

Color LUT: define stops and interpolate.

```js
const stops = [
  [0.00, 8, 12, 28],
  [0.10, 22, 40, 84],
  [0.25, 26, 120, 150],
  [0.45, 60, 190, 140],
  [0.65, 190, 215, 80],
  [0.85, 250, 220, 120],
  [1.00, 255, 250, 235]
];
```

LUT of 512 entries indexed by v mapped: t = v / vmax where vmax = 0.45 maybe. Actually v max in these params ~0.4. Use t = min(1, v*2.2).

Better: use both u and v: brightness could incorporate u. Keep simple.

Now writing the code.

Canvas sizing: display canvas element width/height set to CSS size * devicePixelRatio? Keep simple: fixed canvas attribute size 720x720, CSS width 100% of container with aspect-ratio 1. Use drawImage scaled with smoothing enabled for nicer look (image-rendering: auto). Actually crispness at 256→720 with smoothing gives soft blobby look which is nice for organic patterns. I'll enable smoothing.

Interaction mapping must account for canvas attribute size vs CSS size: use getBoundingClientRect.

Pointer events: pointerdown → painting=true, paint at pos; pointermove → if painting paint; also support hover-with-button? Only painting while down. Use setPointerCapture.

Also touch-action: none on canvas.

Let me write the whole file.

Frame loop:
```js
let lastT = performance.now(), acc=0;
function frame(now){
  if(!paused){ for(let s=0;s<stepsPerFrame;s++) step(); stepCount += stepsPerFrame; }
  render();
  updateStats();
  requestAnimationFrame(frame);
}
```
Cap stepsPerFrame; also adaptive? Keep simple: stepsPerFrame slider default 8.

Maybe adapt: if frame time > 22ms, reduce steps (auto-quality). Nice but optional. I'll add simple adaptive: measure frame duration and if > 30ms reduce effective steps down to 1... but slider conflicts. Skip; just fixed with slider.

Write it.

Grid N=256. Per step ~65k cells; 8 steps = 524k updates; JS should handle ~ that in a few ms. Fine.

Now, stats: compute vSum every 15 frames to avoid cost... it's 65k adds, cheap enough per frame. Compute every frame fine.

UI elements ids: btnPause, btnReset, slider feed/kill/du/dv/steps/brush, stats spans.

Also add preset parameter buttons? Not required; keep feed/kill sliders but defaults fixed. Add "Reset params" maybe. Keep moderate.

Let me write the file now.

Note: `u` and `v` are declared with `const` but then swapped with `let t = u; u = u2;` — that will throw an error! Must fix: declare as `let u`, `let v`. Also `u2`, `v2` as let. Let me fix.

Also `const canvas` etc fine. Let me fix the const issue.

Also `const` in the swap: `let t = u; u = u2; u2 = t; t = v; v = v2; v2 = t;` — `u` is now `let`, fine.

Now run in browser.

Works. Initial seed visible at center. Steps are advancing (80 steps already). Let me check evolution via motion frames, then check console for errors (none reported besides sandbox warning).

Note the frame time 20.4ms — includes stats maybe. Fine.

Let me take a motion check to see evolution, then test pointer seeding.

The pattern is evolving organically (growing, splitting lobes) and ΣV is increasing over frames — live simulation confirmed. Frame time ~12-16 ms, good.

Now test pointer seeding in a separate region. The canvas occupies roughly x from 30 to 833, y from 105 to ~808 (extends below viewport at 800? aspect-ratio 1 on width ~803 → height 803, so canvas extends past viewport). Click at (250, 300) which is upper-left empty area. That's canvas cell x = (250-30)/803*256 ≈ 70, y = (300-105)/803*256 ≈ 62. Fine.

Actually let me click at an area far from the central pattern: e.g. (250, 250). Then drag to another spot.

Let me click and drag: browser drag action with x,y to toX,toY.

The click injected a circular blob at upper-left (visible at ~(230,260)). Now drag to make a stroke, then check that the new region evolves in following frames.

Let me drag from (650, 250) to (750, 350).

Interesting: the drag stroke is visible at upper-right as a blue/dark streak — wait, the stroke appears as a dark (U-depleted) shape with a partial green rim. Hmm, the drag stroke shows the region with a slightly lighter blue background and green rim at the top. That's odd — the injected V should show green. Possibly the drag happened quickly and the painted region's V reacted fast... but within ~1 second, V would grow into a reaction front, not vanish.

Actually looking closer: the top-right area shows a C-shape and a rounded rectangle outline that is dark blue with light rim. That's the U-depleted region (darker due to my U shading? shade = 1 + (u-1)*0.25, so u<1 → darker). The V there seems to have... hmm. Actually the brush adds V=0.55 max, U reduces to 0. With u≈0.45, v≈0.55, uvv = 0.45*0.3=0.14, and kill+feed=0.097*0.55=0.053... v should grow. Actually with u that low, u*v²=0.135 is a big sink for v and consumes u. Reaction: v increases by uvv - (F+K)v = 0.135 - 0.053 = +0.08 per step. u decreases by uvv - F(1-u) = -0.135 + 0.019 = -0.116. So u drops to 0 quickly, then v decays with (F+K) since uvv=0. Meanwhile F(1-u) refills u. Hmm, so a strong spike of V with depleted U may just die out — V decays before U recovers enough to sustain. That is the classic Gray-Scott behavior: an over-strong perturbation kills the reaction locally.

Wait but the earlier click at (230,260) produced a nice green blob that evolved. In the drag frame, the click blob has grown into a whole pattern region at upper-left. That worked.

The drag stroke shows the region has died out (dark) with only the top arc rim still greenish. Hmm — the stroke is at the top-right; the picture shows a C-shaped green arc at top and a dark rounded-rect shape. So the seed is dying. But per the verification requirement: "Check that the added region affects the following frames." It does affect (ΣV increased from 0.0201 to 0.0461... wait that includes central growth).

Better: make the brush gentler so injected seeds survive and grow like the central seed: e.g. set v = min(1, v + 0.35*falloff), u = max(0, u - 0.35*falloff)? But the central seed has u=0.5, v=0.25 — that persists and grows. The brush sets v up to 0.55 and u down to 0.45 at center — similar to seed actually (u0.45, v 0.55). Hmm, higher V is more aggressive.

Actually look at the survival: seeds from clicks did evolve (upper-left region grew into a full pattern). The drag stroke's lower portion died out but the top arc survived and is growing. So mostly works. But to make pointer seeding more reliably persistent, I could use gentler amounts: set target u=0.5, v=0.25 in brush (like the initial seed) blended with falloff, rather than additive ±0.55.

Let me change paint() to blend toward the seed values:
```
const k = 0.85 * falloff; // strength
v[i] = v[i] + (0.25 - v[i]) * k... 
```
Hmm, but if user paints on existing high-V area, that reduces V. Instead: v[i] = max(v[i], ...) plus small addition. Simpler: amt = 0.30 * falloff; v += amt (cap 1), u -= amt (floor 0). With amt 0.30 max: center u≈0.7, v≈0.3 — a milder seed closer to initial seed (u=0.5, v=0.25) at the core... actually falloff gives center amt=0.30 → u=0.7, v=0.3. That's a milder, more survivable seed.

Hmm, but click blob with0.55 worked well. The drag dies because consecutive paints overlap and accumulate up to the cap? No, drag paint applies once per move event; overlapping adds accumulate → v near 1, u near 0 → dies.

So better: clamp toward a target rather than accumulate. Use: v[i] = Math.min(1, Math.max(v[i], 0.35*falloff... )) hmm.

Simplest robust: blend toward seed values with strength falloff:
```
const targetV = 0.35, targetU = 0.45;
const k = 0.9 * falloff;
v[i] += (targetV - v[i]) * k;
u[i] += (targetU - u[i]) * k;
```
This is idempotent-ish: repeated painting converges to (u=0.45, v=0.35) at center, mild enough to survive and grow, and doesn't stack to u=0. Where v already high (>0.35) painting slightly lowers it, fine.

Hmm, v=0.35 with u=0.45: uvv = 0.45*0.1225 = 0.055; (F+K)v = 0.097*0.35 = 0.034 → v grows +0.02/step, u drops 0.036/step until u low... then v decays? Let's check the central seed survival: u=0.5, v=0.25 → uvv = 0.031; (F+K)v = 0.024 → v grows slightly. And it grew into a nice pattern. So (0.45, 0.35) should be a bit more aggressive but still survive. Actually maybe just use exactly the initial seed values (u=0.5, v=0.25) at the brush core so pointer seeding behaves exactly like the reset seed — provably survives. I'll use targetU = 0.5, targetV = 0.28.

Let me implement that and re-test.

Also note the drag test showed things affecting subsequent frames clearly (the click blob grew into a large pattern). But I want the drag stroke to persist to make the behavior obviously correct.

Let me edit paint().

Now add SEED_U / SEED_V constants and use them in reset() too for consistency.

Wait: reset() should restore "the initial fields and seed" — using SEED_V=0.28 instead of 0.25 is fine, it's the same initial condition definition. Fine.

Now reload and test: reset, drag a stroke, pause, verify frozen, resume, reset, compare to initial.

Reload first.

Wait — new Function would fail on `const` redeclaration? No, it just parses/compiles; `u`/`v` are `let` now so compile is fine (execution would fail on document, but we only compiled). Good.

Reload browser and re-test interactions.

Fresh initial state (deterministic seed at center). Now I want to:
1. Capture initial state values (via __sim.stats / sample) — I can't eval directly, but I can use the DOM panel. However for reset comparison, screenshots suffice plus stats values.

Let me pause immediately after reset to record exact initial stats? Instead: verify reset restores initial fields by comparing screenshot after reset with the initial screenshot — visually identical.

Sequence:
a) drag stroke at upper-left region → screenshot (seed appears).
b) motion → screenshot (seed evolves → affects following frames).
c) click Pause → screenshot twice (frozen: steps constant).
d) Resume briefly → steps increases.
e) Reset → screenshot; compare with initial (identical square seed).

Also pause first to show the paused state freeze. Let's do drag now.

The stroke left two visible blobs at upper-left (partially reacted already — they've morphed into curved arcs since some time passed during the drag; V is present and reacting). The seeded regions are clearly visible and reacting. Let me capture motion to confirm they affect following frames (grow/move).

The pointer-seeded region at upper-left grew into a large reaction zone that visibly affects subsequent frames (ΣV rising 0.0421 → 0.0474, pattern expanding). 

Now test pause/resume. Click Pause button at ~(936, 177). Then two screenshots to confirm frozen (steps constant). Then resume, then reset and compare.

Paused state: button now "Resume", status "Paused" with red dot. The pattern has filled the grid (rich coral/labyrinth). Now verify freeze: screenshot twice and compare step counts.

Steps and ΣV identical across paused snapshots (22,032 / 0.0886) — frozen. Now resume and confirm steps advance again.

Resumed: status Running, steps advancing (22,088 in DOM, panel stale at 22,032). Now Reset and compare with initial scene.

Reset restored the identical initial scene: central square seed (green with bright rim) on empty background, steps counter back near0, all pointer-seeded regions cleared. Matches the initial screenshot exactly.

One quick remaining check: keyboard shortcuts (Space/R) and parameter sliders. And "Restore default parameters". Let me test space key quickly and a slider change. Then finish.

Actually time budget — I have done the main checks. Let me do one quick keyboard + slider check in one go: press space (should pause), then press space again? The browser key action presses a key; use text " " or "Space". Let me try key action with text "Space". Then screenshot to check status. Then key "r".

Let me combine: key press space → inspect DOM for "Paused".

Space toggles pause (status "Paused"). Now press "r" to reset while paused → should restore initial fields; then press space to resume. Let me press r and check steps go to 0 and seed appears.

Actually the pause was triggered by Space — but did the keydown target get excluded? It worked. Now press "r".

R while paused resets exactly (steps 0, center V 0.2800 = SEED_V, sharp square seed as rendered before any diffusion). Matches the initial condition exactly.

Everything works. One last thing: parameter sliders — the value labels are correct at defaults; I could quickly verify a slider changes the displayed value and simulation (e.g., Feed slider). But that's optional; sliders use a well-tested binding (initial apply() worked since labels show 0.160 etc.). I'll skip deep slider verification but do one quick drag on the Feed slider to confirm the label updates — cheap.

Actually, let me resume first so the sim is left running, and do a quick slider test.

Feed slider at ~(988, 615); drag to (1088, 615) to increase feed → label should change to ~0.058.

Slider works (Feed label 0.064). Now restore default parameters and resume so app is in a clean running state, and finalize. Let me click "Restore default parameters" and "Resume", then done. Actually the app state in browser doesn't matter to the file — the file is already saved and complete. Let me just do one quick restore+resume click to leave it running, verify, and report.

Actually simplest: click "Restore default parameters" (which resets sim to defaults and resets fields) and then Resume. That's 2 clicks. Keep it brief — one click on "Restore default parameters", then a screenshot to confirm defaults, then finish. Time is short; do both in sequence quickly.

The "Restore default parameters" button is below the fold. Instead just set the Feed slider back by dragging back to the default position (988, 615), and press Space to resume. Then finalize.

Actually the app defaults in the HTML file are correct regardless; only my browser session state is modified. To finish quickly: drag feed slider back to default, press Space to resume, verify, done.

Feed slider back near0.036 (drag granularity — essentially default; the HTML file itself has value="0.035" so a fresh load is exact). Good enough.

Final: verify the file exists and is complete. Then report. Press Space to resume so it's running? Not necessary. Just confirm file.

Quick sanity: ls and confirm index.html size.

File saved: /tmp/job-SmEyrI/index.html (20KB, single self-contained file). Done — report.