Boids flocking · mimo-v2.6-pro

Let me build the file. Single self-contained index.html with canvas flocking.

I'll write a solid implementation: spatial grid maybe not needed for 150 boids (O(n²)=22500 ops/frame, fine).

Features:
- Full-screen canvas, resize handling with devicePixelRatio.
- 150 boids, triangles oriented by velocity angle.
- Separation, alignment, cohesion, speed limits, steering force limits.
- Cursor repulsion radius visible (draw circle outline around pointer) — "visible or documented" — I'll draw a subtle circle and document in a small help text.
- Pause/Resume button, Reset button, maybe speed slider optional (keep simple but useful). Controls must remain usable after resizing — HTML overlay controls fixed.
- Wrap edges.
- Trails optional — keep it clean with slight fade.

Let me write it.

Then run browser checks: screenshot at moments, click pause/resume, mouse move.

Let me write the code carefully.

Key details:
- Boids stored as {x,y,vx,vy}.
- maxSpeed ~ 3.2 px/frame at 60fps, maxForce ~0.06... typical: maxForce 0.05? Let's use normalized forces scaled.

Implementation of steering: desired = normalize(target - pos)*maxSpeed; steer = desired - vel; limit to maxForce.

Separation: sum of (pos - other.pos)/dist weighted by 1/dist, desired speed maxSpeed.

Cursor: if dist < influenceRadius (e.g. 140), desired = normalize(pos - pointer)*maxSpeed * strength ramp; steer limited.

Also add slight speed min to avoid stalling? Fine.

Rendering: clear with rgba fill for slight trails (0.25 alpha). Triangles: draw path relative to position with rotation by angle of velocity.

Stats display: count of boids, maybe avg speed — optional.

Edge wrap: if x < -margin => x = w + margin etc. With triangle drawing at edges, wrap with margin of ~10.

Pointer influence radius visible: draw dashed circle at pointer when active.

Resize: set canvas width = innerWidth*dpr, style 100vw/100vh, ctx.setTransform(dpr,0,0,dpr,0,0). Keep boids in bounds (clamp positions to new size).

Controls: fixed top-right panel with buttons Pause/Resume toggle and Reset, plus pointer radius info text, plus maybe a slider for influence radius. Keep controls fixed position with pointer-events auto so they don't block canvas? Mouse influence: listen on window pointermove.

Also handle pause: freeze state — stop updating physics; keep rendering? Pause freezes simulation state; I can still render (static). Simplest: rAF loop always draws, but skips update when paused. But trails fade would blur frozen image — instead when paused, don't fade. Actually fading clears the frame each tick; drawing re-renders boids at same positions so image stays static except fade. Fine: skip fade when paused, and just redraw boids. Actually to be safe, when paused skip rendering entirely except first frame after pause... simpler: always clear fully (no trails) and draw boids; frozen image identical each frame. I'll skip trails for crispness and use full clear. But motion trails look nice... Let's do slight fade only when running: fillStyle rgba(10,14,26,0.35) when running, full clear when paused... that would change appearance on pause slightly. Just do full clear each frame — simplest and deterministic. Actually a mild trail helps visual "coordinated movement". I'll skip trails for correctness of freeze.

Hmm, but with full clear, if paused and we keep rendering, image is static — good.

Let's write.

Also keyboard: Space toggles pause, R resets. Nice extra.

Time step: use fixed dt based on rAF delta clamped, scale forces by dt*60? Keep frame-based with delta normalization: use `dt = min(delta/16.67, 2)`.

Write file now.

Boids init: random positions, random headings with speed ~1.5.

Rendering triangle: size 6-9 based on speed maybe. Draw:
ctx.save(); ctx.translate(x,y); ctx.rotate(angle); path: moveTo(size,0); lineTo(-size*0.7, size*0.55); lineTo(-size*0.35,0); lineTo(-size*0.7,-size*0.55); closePath. Fill with color varying by heading or speed. Add stroke.

Color: hue based on angle, e.g. hue = (angle in degrees + 360) % 360 mapped to 180-320. Nice.

Also draw velocity direction indicator? Not needed.

Perf: 150 boids fine.

Write the file.

Then browser: load index.html via browser tool (it runs index.html in cwd). Take screenshot, inspect console. Do motion check maybe. Interact: click Pause button — need coordinates. I can inspect DOM to find button positions.

Let me write.

Code details for neighbor loops: O(n²) with separation etc. Compute in one pass per boid over all others.

Let me produce the HTML.

For "documented cursor-influence radius": include a line in the UI panel: "Pointer influence radius: 140 px (boids steer away from the cursor)". Also draw circle.

Reset: reinit positions/velocities and also maybe keep paused state.

Resize: window resize listener + visualViewport? Just resize event and also check on each frame cheaply? Use ResizeObserver on document.documentElement maybe. Use window 'resize'.

Population stays 150 after resize.

Now write.

There's a leftover odd line in alignment: `alignX / alignN - b.vx + b.vx * 0` — that's just alignX/alignN - b.vx... wait, steerTowards already converts direction to maxSpeed, so passing `avg - b.vx` is a direction vector which then gets normalized — fine-ish but weird. Better to just pass average velocity direction: `steerTowards(b, alignX/alignN, alignY/alignN, w)`. Let me clean that up.

Then run browser.

Wait: steerTowards(b, avgVx, avgVy) treats avg velocity as a direction and normalizes it then scales to maxSpeed — that's fine for alignment.

Now run the browser.

Rendering works. But the flock appears dispersed — no visible grouping yet (initial state, just started). Also there's a leftover pointer ring at top-left corner (pointer.active from initial state? Actually pointer.x=-9999... the ring drawn at top-left shows a partial circle — hmm, at (-9999,-9999) it wouldn't be visible. The visible arc in top-left suggests pointer position somewhere near (-30,-30)? Maybe pointermove fired during reload with coordinates... Actually the browser tool may move mouse. It shows dashed circle centered around (-30,-30)? Arc visible at top-left. That's from pointer.active being true with coordinates set by a pointermove event near (0,0). Fine — it's the influence ring showing where the pointer is.

Hmm wait, it might be that pointermove events fired with clientX/Y = 0. It's fine visually.

Now, flocking cohesion: 150 boids over 1200x800 with perception 72 — sparse initially, groups may take a while to form. Cohesion weight 0.85 vs separation 1.75 — could be ok. Let me check motion frames and whether groups form.

Let me take a motion sample and check group formation over time. Also verify triangle orientation matches travel direction — I can inspect via JS in console... the browser tool has "inspect" which gives DOM/console. I could add a temporary check... Better: use the browser tool's motion to see movement, and do a mathematical check by injecting a script? The tool doesn't support arbitrary JS eval except through page. Alternative: I can reason from code — angle = atan2(vy,vx), triangle nose at +x — correct.

But the verification request says "Sample the flock at several moments to check coordinated movement and triangles pointing along their travel direction." I can do that visually via screenshots/motion frames.

Let me first wait a bit and screenshot to see if groups form. Use motion action.

Also fix: the fps shows "— fps" — after 500ms it should update. Fine.

Let me run motion to see frames.

Excellent — clear flocking: multiple coherent groups with aligned headings (groups of blue/cyan pointing down-right, yellow/green pointing right, etc.). Triangles point along their heading — e.g., in frame 4, the top-left cluster points down-right consistent with movement direction across frames.60 fps.

But the flock drifts up-left and clumps toward the top-left corner. The soft edge steering pushes back, but cohesion is strong. It's okay-ish; flock seems to drift into the top-left corner and stay. Actually the dashed pointer ring at top-left corner (0,0) is acting as a repulsor keeping them away from that corner... interesting: the pointer appears "active" at top-left corner because the harness left a pointer position? Actually pointer.active got set by a pointermove somewhere. The ring center is around (-30,-30) — odd. Whatever.

Concern: flocking clumps into2-3 tight groups which is fine ("form moving groups").

One issue: boids pile toward top-left; the edge steering weight may be insufficient against cohesion. Could increase edge steering or add a mild centering force. Let's see later frames. Also flock could collapse into a dense ball. Let's check more frames and pointer interaction.

Now test pointer interaction: move pointer into flock area and screenshot. Use browser drag or click? "pointermove" — the browser tool has click and drag. drag with toX/toY might generate pointermove. Let me drag from one point to another without... drag would simulate mouse down-move-up. pointerdown sets pointer active, moves set it. That works.

Let's drag across the flock region, e.g. from (400,300) to (500,350).

Also verify orientation mathematically? Visual check looks right: e.g. frame 1 top-left cluster boids point down-right (nose toward +x rotated) — headings matched. Good enough.

Let me do pointer test.

Cursor avoidance works beautifully — a clear void forms inside the influence circle (centered ~420,320), boids ring around it pointing away from the pointer. 

Now test pause: click Pause button at (972,133). Then screenshot twice to confirm frozen.

Paused state active (button says "Resume", dot orange). Boids here are strongly aligned (flock moving left together). Now capture two motion frames to verify frozen state.

All 4 frames identical → frozen while paused. Now resume and confirm motion continues. Then test Reset and a resize. Let me resume (click Resume) and then motion.

Resumed (Running, green dot). Now test Reset: click Reset (1104,133) then screenshot to confirm a fresh scattered population of 150. Then do a resize check — the browser tool viewport is fixed at 1200x800; I can't resize. But I can verify the resize handler logic by code review and maybe by simulating? Not directly available. I'll note as partially verified: I can at least confirm controls remain visible and canvas covers viewport (it does at 1200x800). Could I test resize via CSS? Not easily. I'll state it as unverified beyond code review.

Actually, maybe I can trigger a resize programmatically... The browser tool runs the page in an iframe with sandbox; can't eval JS directly. Fine.

Let me click Reset.

Reset restored a fresh scattered population of 150 boids across the viewport. Boid count still 150.

Now: verify motion resumes after reset (obviously), and that the flock resumes flocking after pointer moves away — earlier the pointer ring stayed near top-left corner even after drag... Hmm, after drag to (420,330), the ring was at (420,320). Then when clicking the Pause button, the ring moved to top-right near (890,60)? Because the click moved pointer to (972,133) — but the ring appeared centered near (880, 60)... it seems ring center is offset. Actually the ring in the paused screenshot appears centered around (890, 60)-ish with radius 140, meaning pointer at approximately (890,60)? But the click was at (972,133). Hmm, radius 140 circle visible: leftmost arc at x≈835, so center x≈835+140=975 → center≈ (975, 133)? But the visible arc appeared at top-right region spanning x 835-940, y 0-190. Center (975,133) with r=140 would span x 835-1115, y -7 to 273 — matches (arc visible on left side of circle, right side hidden behind panel). Yes! consistent. Good.

One residual issue: the influence ring remains "active" after pointer leaves the flock area — that's correct behavior (repels boids near pointer).

But there's a concern: when the pointer is over the UI panel, boids near the panel get repelled — acceptable.

Also earlier the initial screenshot showed a ring at top-left corner — that's because a pointermove at (0,0)-ish fired. Fine.

Now test "resume flocking after pointer moves away": move pointer to empty bottom-right area and take a screenshot later to see flocks reform. Well, we already saw flocking reform after the drag earlier (paused screenshot showed coherent aligned groups). That's evidence enough.

One more check: keyboard Space toggle. Let me press Space via browser key action and check DOM says "Resume"/"Paused", then press R... Actually key action: browser key with text " "? Let's try text "Space".

Also I should double check the "boids near pointer" strength and general stability over long run (no NaN). Let's run motion a couple more times after reset to confirm movement and no errors.

Let me do: key "Space" → check paused; key "Space" → running; key "r" → count150.

Then final screenshot.

Also verify triangle orientation vs travel direction programmatically would be nice. I could add a tiny debug hook... Instead, visual: in the paused frame, the main cluster triangles pointed left (nose left) while the cluster drifted left across frames — consistent. And in the cursor frame, boids ringed the void pointing outward — consistent with steering away. Good.

Let me do the keyboard checks.

Space paused it. Groups re-formed already (top-left cluster aligned leftward/nose right? Their noses point right-ish while... hmm hard to say). Now press Space again to resume, then R to reset — but pressing R resets the population. Let me press Space (resume) and verify running, then press "r" and verify 150 and fresh. Then a final screenshot sampling.

Actually to also verify "resume flocking after pointer moves away" — pointer is at top-right corner near panel. Flock formed groups away from it; fine.

Press Space to resume.

Running again. Now press "r" to reset via keyboard and then sample motion to confirm continued movement + pointer avoidance once more. Then done.

Actually, a final sampling of motion after reset confirms everything continues. Let me press "r" and then do motion once.

R reset works. Now a final motion sample to confirm continued coordinated motion. Actually I've already verified motion multiple times. One last quick motion to be safe and then report.

Also I want to double-check the file is complete and valid — quick sanity: no external resources (grep for http). Let me grep.

Everything works. No external resources (grep found nothing besides maybe nothing — output showed no matches). Single file, 618 lines.

Interesting: the tool hints there's a hidden panel ".home" dir but irrelevant.

One notable observation across frames: groups form and move coherently; triangles point along travel (e.g., bottom-right cluster of cyan triangles pointing right while the group translates right/down across frames — matches).

Done. Report.

Unverified: resize behavior (browser viewport fixed at 1200×800 — couldn't trigger a resize event), touch/pointer events beyond mouse drag/click, and long-run stability beyond ~1 minute. Also the alignment/cohesion are visually confirmed but no numeric metrics computed.

Note the file: /tmp/job-xg14sx/index.html.