Reaction-diffusion · qwen3.8-max-0902

Let me build it. Use Canvas 2D and ImageData for the grid (e.g., 160x160 or 192x192). Standard Gray-Scott with Du=0.16, Dv=0.08, dt=1.0 gives stable patterns. Use a Laplacian with 9-point or 5-point stencil. Steps per frame around 8–16.

Write index.html, test with the browser tool: sample the field, simulate clicks/drags, pause/resume, reset.

Add JS hooks for verification: maybe expose sim state globally. Write it with the following functions: init(), step(), render(), pointer handlers. Expose window.sim = {u, v, N, paused, ...} so the browser tool can inspect. Use the browser's "inspect" or eval? The browser tool has actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. "inspect" probably evaluates JS or dumps the DOM/console. Let's just write it and try.

Plan: N=180, dt=1.0, Du=0.16, Dv=0.08, f=0.035, k=0.062. 5-point Laplacian: lap = (neighbors sum - 4*center). Scale by dt. This is standard and gives stable mitosis/coral-like patterns with f=0.035 k=0.062... actually, f=0.035, k=0.062 is in the "coral growth" region. Good.

Seeding: fill the center with a small square of V=1, U=0.5, with a bit of noise added if needed.

Rendering: map V to color with ImageData, scale up with ctx.putImageData? putImageData doesn't scale. Better approach: draw to a small offscreen canvas, then drawImage with imageSmoothing disabled/enabled to scale. Colors: low V = dark blue, high V = bright.

Interaction: pointerdown/pointermove -> addBrush(x,y): in a radius, v += ..., u -= ....

Controls: pause/resume button, reset button, and step count if needed.

Verify with the browser tool. Let's write it.

Note: window.sim is using a getter that references the local variable u which gets swapped out, but since u gets reassigned inside integrate, this isn't a problem. The getter returns the current binding, so... actually, `get u() { return u; }` captures the variable `u` via closure, and reassignments are visible too. Nice.

Let's verify in the browser.

The simulation is running. Initial seed is displayed in the center. At step 40-80, the seed is diffusing. With f=0.035, k=0.062, the pattern should grow from the seed. Let me check the evolution — wait a bit, then take a screenshot. The "motion" action might let me sample frames over time. Let me wait a few seconds and then take a screenshot. The browser tool doesn't have an explicit wait, but "motion" captures frames over time. Let me try using motion.

The pattern is evolving organically (spots growing and splitting). Good. Colors: teal-colored pattern on a dark background — visible but a bit dark. The pattern's V values in this parameter region might be around 0.3–0.4, so the color is in the teal band. No problem, but I could boost the contrast. The pattern looks a bit dark. Maybe I can improve the color mapping: normalize by the typical max value of V (around 0.4). Let me try scaling m = v * 2.2 clamped. This should brighten the pattern.

Next, verification: seed another region with the pointer (click), and confirm that the added region affects subsequent frames. Then pause/resume, reset, and compare.

First improve the contrast, then run the interaction tests.

Color mapping adjustment: m = min(1, v * 2.5). The background U=1 gives base=0.55 -> coefficient (0.5+base)=1.05 for the dark band... wait, when m<0.5, r,g,b are multiplied by (0.5+base), and base = uc*0.55. When uc=1, coefficient = 1.05. Background (m=0): (8,12,28)*1.05 ≈ (8.4,12.6,29.4) dark navy. Good.

When m=0.5: (20,130,140)*1.05 = (21,136,147) teal. When m=1: (255,190,80) amber. With scaling v*2.5, v=0.4 -> m=1 -> amber. The core of the pattern becomes amber/bright. Good contrast.

Let me edit the render function: var m = vc * 2.5; if (m>1) m=1.

Then reload and test interactions:
1. Click a certain point (e.g., 400,200 in canvas coordinates). Canvas viewport: the stage spans x 321-879, y 76-634. Click (450, 200).
2. Confirm that v is high at the corresponding grid cell — can I evaluate JS with the browser tool? The "inspect" action might return the DOM/console. There's no eval action. Hmm. Available actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. No direct JS eval. But can I use key/type? Not for eval.

Alternative verification method: visual — after clicking, the screenshot should show a bright blob at the click location; subsequent frames should show that it affects the evolution (pattern growth from that location). This satisfies "confirm that the added region affects subsequent frames" via visual confirmation.

For pause: click the Pause button, take 2 screenshots, confirm they are identical (step counter is static). Resume: steps increase. Reset: the central seed is restored to the initial scene (compare with the first screenshot).

Also, the DOM text includes a step counter, which helps confirm pausing.

Let me first edit the colors, then reload.

Reload, and take a screenshot after a little while. After that, click another region.

Contrast has been improved: amber-colored seed edges on a dark navy background. Next, drag to seed a separate region: drag from (420,220) to (500,260). Then take a screenshot to confirm the added region and its effect on subsequent frames.

The drag stroke is displayed in the upper left (an amber-colored capsule). Next, confirm that it affects subsequent frames: take another screenshot after a while (motion) and check whether the stroke has developed into a growing pattern (spots).

The seeded stroke region grew into a coral-like pattern spreading across the entire upper-left area — clearly affecting subsequent frames. The pattern is a beautiful organic "coral growth" (f=0.035, k=0.062).

Next, test pause/resume: click the Pause button, take 2 screenshots at intervals, and confirm that the step counter is fixed and the images are identical. Then resume and confirm that steps advance. After that, reset and compare with the initial scene (central square seed).

Paused at step 12050, status is "paused", button displays "Resume". Confirm that the frame is static: take another screenshot after a delay (motion) — the step count should remain 12050 and the image should not change. After that, click Resume and confirm that the step count increases. Then Reset.

The frames during the ~1.6 second pause are identical, and the step count stays fixed at 12050. Next, click Resume and confirm that the step count advances, then click Reset and compare the initial scene with the central seed.

Resumed (steps advanced from 12050 → 12080, status is running). Next, click Reset and compare with the initial scene (the square seed in the center).

Reset restored the initial scene: dark field with the central square seed (steps reset to about 10–30, matching the first screenshot at steps 30: central square with amber border and teal interior). Matches the initial scene (the first reload screenshot at step 30 showed a square with amber border/teal center — identical).

All required behaviors verified:
- Field evolves (steps increase, patterns grow organically) ✓
- Wrapping square grid, parameters as specified ✓ (parameters in code)
- Initial U=1, V=0 + central seed ✓ (first frame)
- Contrasting colors ✓
- Click/drag adds V and reduces U ✓ (drag strokes appear and evolve)
- Added regions affect subsequent frames ✓ (coral growth from stroke area)
- Pause/resume ✓ (fixed at 12050 for about 1.6s, then progresses)
- Reset restores initial field/seed ✓ (matches first scene)
- Work per frame is bounded (10 steps), resolution 180² ✓

One more simple check: single click (not drag). The drag test already covers pointerdown+move. Click is essentially pointerdown. No problem.

Also confirmed no console errors: only sandbox iframe warnings from the harness, none from the app.

Done. Final file exists. Reporting.