Boids flocking · deepseek-v4.1-flash

Let me build this. I'll write the index.html file with a canvas flocking simulation.

Let me think about the implementation carefully:

- 150 boids, triangles oriented in direction of travel
- separation, alignment, cohesion
- bounded speed and steering
- wrap edges
- cursor influence radius, steer away from pointer
- Pause/Resume and Reset buttons
- canvas fits viewport, population and controls usable after resize

Let me write it.

Flocking parameters:
- separation radius ~ 25
- perception radius ~ 60
- max speed ~ 3
- max force ~ 0.05

I'll implement with a spatial grid for performance (150 is small, O(n²) fine).

Let me write the file.

For cursor interaction: track mouse position, when within influence radius (say 120), add repulsion force scaled by proximity.

Direction of travel: velocity angle. Draw triangle pointing in +x direction then rotate.

Let me write it all.

I'll make controls fixed at top-left with buttons and a boid count display. Pause toggles. Reset reinitializes.

Also handle pointer leave - set pointer inactive.

Let me write the code.

For resize: set canvas width/height to window dimensions, handle devicePixelRatio maybe. Keep simple but crisp.

Let me draw triangle relative to size.

I'll use requestAnimationFrame with delta time normalized.

Let me code it.

Flocking math:

For each boid:
- steer = (0,0)
- sep, ali, coh accumulators
- iterate others:
  - d = distance
  - if d < perception:
    - alignment: sum others velocity
    - cohesion: sum others position
    - if d < separationRadius: separation += (this.pos - other.pos)/d (weighted)
- Apply forces:
  - separation: normalize, scale maxSpeed, subtract velocity, limit maxForce, weight 1.5
  - alignment: same weight 1.0
  - cohesion: same weight 1.0
  - pointer avoidance weight 3.0

Speed clamping: if speed > maxSpeed scale down; if < minSpeed set to minSpeed.

Let me just write.

I'll include a documented cursor radius shown maybe as a faint circle near pointer? "visible or documented cursor-influence radius" - I can draw a faint circle around the pointer to make it visible. That's nice.

Let me write the HTML.

I need to be careful with tool: write file to /tmp/job-Wlipua/index.html.

Let me write it now.

Let me write the index.html.

I noticed a bug: in `resize()` I reference `boids` before `spawn()` is called (resize is called before spawn at boot). `for (const b of boids)` — boids is initialized to `[]`, so it's fine. Good.

Let me run the browser and inspect.

The simulation renders. Boids are moving and flocking. I see a dashed cursor circle at top-left (from pointer position). Maybe pointer is at 0,0-ish causing boids near top-left to steer away. That's fine.

Let me test pause/resume and cursor interaction. First, let me capture a couple frames to verify motion. Then click pause, capture, verify frozen. Then click resume, verify moves.

The snapshot shows boids with motion trails, looking like oriented triangles. Good.

Let me test pause. I'll click Pause at ~(50,38). Then take two screenshots/motion frames.

Actually let me take a motion capture first. The "motion" action captures frames. Let me use it.

Motion across frames shows coordinated movement and flocking groups forming, triangles pointing along travel. Good.

Now let me test pause. Click the Pause button at approximately (51, 37).

Button now says "Resume" and aria-pressed presumably true. Let me take two screenshots to verify frozen state.

The screenshot after pause is identical to the paused click screenshot — boids frozen in same positions. Trails fade though (background fade continues), but boid positions identical. Good — frozen.

Now test cursor interaction while paused? Actually cursor interaction requires running. Let me resume, then move pointer into flock and observe avoidance. Let me resume first.

Actually, let me test cursor interaction before resume isn't useful since paused. Resume then drag pointer.

Let me click Resume.

Resumed. Now the pointer is near top-left (0,0 area) and boids there avoid it. Let me move pointer to a dense flock e.g. around (600, 690) where many boids are. Then capture screenshot to see avoidance and move away to check resume.

The browser tool pointer actions: "click" moves pointer there. But clicking might trigger button etc. I can use "drag" perhaps to move pointer without releasing? Or "click" on empty canvas will set pointer active at that point. Since pointerdown on window doesn't interfere except setting pointer. Clicking canvas is fine.

Let me click at (600, 690) in the dense flock.

The cursor radius circle is visible at (600, 690). Boids inside the circle appear to have moved out; there's a clear gap in the center of the circle. The flock that was at ~(600,690) has been pushed outward. Good. The density is lower inside the circle. The nearby group moved to the right. This demonstrates avoidance.

Let me move pointer away and verify they resume flocking. Move to say (100,400) and wait then capture.

Actually the avoidance works. Let me move pointer off to corner (1180, 760) and take a motion to see flocking resume.

Also I should test Reset. Let me test reset restores 150. It's hard to count, but boid count text stays 150. Reset reinitializes positions.

Let me test reset button click - already at (123,37). It should scatter boids. But note pointer position stays; pointer.active remains. Fine.

Let me first move away and check resume.

Pointer moved to bottom-right corner. The circle is there. Boids have regrouped into coherent flocks and are moving together, all triangles pointing in their travel direction (aligned). Good — flocking resumed.

Now test Reset. Click Reset at ~(148,37).

Reset scattered the boids into a fresh population spread across the screen, count still 150. Good.

Now test resize. The addendum mentions keeping population/controls usable after resizing. The browser tool viewport is fixed 1200x800 though. I can't easily resize via tool. I can check code logic. But maybe I could trigger a window resize via inspect? Not available. Resize handler code is sound: clamps boids, repaints. Good enough.

Actually, one concern: resize during pause? resize repaints background at alpha 1 which clears trails; that's fine.

Another concern: after reset while paused, boids scatter but stay frozen. Reset calls paintBackground(1). Fine.

Let me consider a subtle bug in the pause freeze: when paused, the frame loop still paints background with TRAIL_ALPHA each frame, so trails fade over time, but boid positions are frozen. That's acceptable ("freezes simulation state"). Fine.

One more potential issue: `resize()` is called before `spawn()`, and it iterates `boids` which is `[]` at that point — fine because `let boids = [];` is declared before resize is invoked at boot. Wait, order: `let boids = [];` declared near top after class. Then functions. Then boot calls resize(). Yes boids defined. Good.

Check the initial pointer: pointer.active=false, so no circle until move. In first screenshot there was a circle at top-left because inspect moved pointer? Actually first screenshot showed circle. Fine.

Let me verify no console errors — only the sandbox warning. Good.

Potential improvement: On resize, MIN_SPEED etc are fine. Canvas drawing coordinates use CSS px. Good.

Let me double check triangle orientation. The triangle geometry: nose at (size*1.5, 0) = (10.5, 0), which after rotate(atan2(vy,vx)) points along velocity. Correct.

I think everything works. Let me also verify keyboard space works? Not required but nice. I'll skip.

One thing: the hint says "Click Pause to freeze" but button is Pause/Resume. Fine.

Let me check file exists and is self-contained (no external). Quick grep.

Everything is verified. Let me write a brief report.

Actually, let me also verify resize logic by simulating? The tool viewport is fixed. I could inject a resize via... no eval tool. I'll note it as unverified.

Let me report.