Fireworks · step-5-preview

Playwright is available. Let me check the browser tool.

Let me write the index.html file.

Design: full-screen canvas, click to launch shell from bottom toward clicked location. Shell is a bright dot with trail. On reaching target (or after time), explode into radial particles with gravity, fade, removed after lifetime.

Add UI: Clear button, maybe some controls (burst size, gravity, auto-launch toggle). Keep controls usable after resizing — meaning buttons should be positioned so resize doesn't break them; canvas resizes handle DPR.

Let me write a nice implementation:

- Canvas with devicePixelRatio scaling, resize listener.
- Particles: shells (with velocity), spark particles, and trail particles.
- Trails: draw with fade approach — clear canvas with low-alpha fill to leave trails? But then Clear needs to fully clear. Better: each particle keeps its own trail history (positions) and draw line segments. That gives crisp "trails" and resizing works.

Actually a common approach: composite 'destination-out' fade with globalAlpha for trails. But for resizing, we redraw. Let's use per-particle trail arrays — deterministic and easy to clear.

Shell: rises from bottom at x near click x (jitter), with initial velocity computed to reach target apex at click point. Use ballistic: given target (tx,ty) and gravity g, launch from (sx, sy). Choose flight time T, then vx=(tx-sx)/T, vy=(ty-sy)/T - 0.5*g*T. Then after T, it's at target apex with velocity (vx, vy+g*T) roughly. Explode there.

Actually explode when shell passes apex or timer done. Simple: shell has fuse time T; when elapsed >= T, explode at current position. That lands exactly at target if no drag. Add slight air drag maybe. Keep simple: no drag on shell but slight drag on burst particles? For visuals, add small drag on particles.

Burst: radial particles count ~ 60-120, colors from a palette (HSL ring or random hue). Add secondary effects: crackle, glitter (flicker alpha), double-ring shells.

Particles: pos, vel, gravity, drag, life, maxLife, size, color(h,s,l), trail array, type ('spark'|'glitter'|'streak').

Rendering: for each particle, draw polyline of trail with lineWidth tapered, color with alpha fade.

Also a "flash" burst glow on explosion — expanding fading circle.

UI: header/title, hint text, buttons: Clear, Auto (toggle), and maybe a slider for burst size. Use HTML overlay div positioned fixed; on resize, keep it in view (fixed positioning handles that). Also handle canvas resizing keeping particles' coordinates — they're in CSS pixel space, fine.

Keyboard: Space = launch random, C = clear.

Performance: cap particle count.

Let me write it.

Details on trails: store trail as array of {x,y} with max length. Push each frame. Draw with strokeStyle hsla. Use lineCap round.

For trail fade, older segments have lower alpha — simpler: draw whole trail at alpha = particle alpha, with lineWidth smaller at tail. Let's do per-segment alpha gradient: iterate segments and lerp alpha from 0 to alpha. That's more strokes but fine for ~2000 particles... Each segment stroke = 2000 particles * 10 segments = 20000 strokes — too slow. Alternative: single path per particle with global alpha = particle alpha * 0.6, and main head dot at full alpha. That's 1 stroke + 1 dot per particle. Good.

Add "sparkle" flicker for some particles.

Let me also add smoke puffs maybe — skip, keep it clean but add glowing explosion flash.

Let's write code.

Time step: use dt clamped, fixed-ish update with seconds.

I'll write it now.

Also the auto demo shell on load: launch after ~600ms toward upper-center-ish random point.

Let me be careful: "Launch one demonstration shell automatically on initial load" — exactly one. Then subsequent shells respond to clicks. I'll have auto-toggle default off (just the one demo), but provide an "Auto" toggle button for extra. That satisfies requirement: one on load.

Now write file.

Canvas sizing: 
```
function resize(){
  const dpr = Math.min(window.devicePixelRatio||1, 2);
  W = canvas.clientWidth; H = canvas.clientHeight;
  canvas.width = W*dpr; canvas.height=H*dpr;
  ctx.setTransform(dpr,0,0,dpr,0,0);
}
```
Canvas CSS: position fixed; inset 0; width 100%; height 100%; display block.

Use ResizeObserver on document/window resize + orientationchange.

Controls: a panel top-left with title and buttons; make sure pointer events on panel don't launch shells (stopPropagation / check event target).

Click handler on window/canvas: pointerdown on canvas only.

Let me write the code with a small FPS/counter display maybe. Include particle count.

Palette: hues arrays: [0, 30, 45, 60, 120, 190, 210, 280, 320]. Burst chooses base hue and spreads.

Write now.

Now let's test in the browser with playwright. Let me write a test script.

playwright resolves from /app/pipeline. Let me run the test from that directory.

Can't write there. Use createRequire approach in a .cjs file in /tmp.

Some observations:

1. "post-resize click" shows 0 particles and 0 lit after 900ms — suspicious. The click at (300,200) on a 600x500 viewport. The stats update only every 0.5s, so 900ms should have updated. Hmm, but maybe the shell is still ascending (T computed from H=500 → about 0.9-1.2s), and the click was at y=200 with H=500 so apexY = 200... the shell should explode at ~1s. But we waited 900ms — borderline. Also `lit` = 0 means nothing drawn on canvas at all. Wait — after resize, the canvas is resized, and `ctx.clearRect(0,0,W,H)` uses updated W/H. But if a shell was rising, we should see it. Hmm, lit=0 with 0 shells and 0 parts means... the click was registered? Let's check: after resize, the stats showed fps 52 which means it updated. But shells=0.

Wait — the issue might be that after resize the canvas element's CSS size changed but... hmm. Actually a concern: `page.setViewportSize` resizes the page; canvas has width:100%/height:100% via inset 0, so clientWidth updates, ResizeObserver fires resize(). Fine.

But lit=0 after clicking. Possibly the pointerdown handler was blocked because... hmm, the `#ui` panel? At 600x500 viewport, the UI panel max-width is min(92vw, 300px) = 276px, and it has padding... the panel height maybe ~230px. Click at (300, 200) — x=300 > 276+14=290, so outside. y=200 might be within panel's vertical range but x is beyond. So click should be on canvas. Hmm.

Wait, actually the overlay `#stars` has z-index 0 and `pointer-events:none`, canvas has no z-index (auto). Body children: canvas (position fixed, z-index auto → z=0 effectively), #stars z-index 0, #ui z-index 5, #hint z-index 4. So canvas is above? Both canvas and #stars have z-index 0 (auto vs 0). Painting order: canvas is first in DOM, #stars second, so #stars paints above canvas. pointer-events none so fine.

So why did the click not launch? Let me check "overlap" after: shells=2 parts=38 — those 4 clicks did register. So clicks work after resize.

Hmm, "post-resize click" showed 0/0. Let me re-test more carefully — maybe the resize happened and the shell launched but exploded... no, parts=0 and lit=0 means nothing was drawn for 900ms.

Possibility: the resize triggered a canvas resize (setting canvas.width clears the canvas) and... no.

Another possibility: The stats were showing stale values because fps update interval... no, shells count updates every 0.5s along with fps.

Hmm, another: `page.setViewportSize` while a pointer is... The click at 300,200 — wait, after resize to 600x500, the `#hint` element is `display:none` under 520px width... it's 600 so shown. pointer-events none anyway.

Actually! Look at "after resize: shells 0, parts 0, lit 0, fps 52". fps updated to 52, meaning 0.5s had elapsed since last stats update. Then click, then 900ms wait, then read shells=0. If the click launched a shell, at 900ms the shell might have already exploded and particles died? No — particles live 1-2s.

Unless... the click launched a shell that immediately died? `dead = s.t >= s.fuse || s.y < 8 || s.y > H + 60`. If the shell is launched from sy = H+12 = 512, and it moves up. Fine.

Hmm wait, maybe the issue: `page.mouse.click(300, 200)` — but the previous action was `page.click('#btnClear')`. Playwright's mouse.click dispatches mousedown/mouseup. Our handler listens for 'pointerdown'. Should work.

Let me just re-test that specific sequence with more logging. Also possible: the canvas didn't resize immediately and W/H were stale... doesn't matter for click.

Actually — hold on. Important: `resize()` sets `canvas.width`, which CLEARS the canvas bitmap. In `render()` we call clearRect each frame anyway. Fine.

Let me just re-run a focused test on the resize case. Also I want to check the initial state: at 400ms the demo shell hasn't launched yet? It fired — "ascent 1" shows shells=1. Good. But `lit=58` at initial and grows. Fine.

Also I notice the burst particle count reaches only ~147 while I intended 70-125 per burst plus crackle 26 → should be ~200. Hmm, at "post 6": parts=147. Two bursts happened (demo + click) plus muzzle/exhaust. Particles die off. Actually the demo burst happened before the click. So 147 remaining from a burst that already started. Plausible.

Wait, but 'double'/'ring' styles etc. Let's check particle counts at peak. In "auto" test parts=333 for ~2 bursts... fine.

Also concern: fps 55-60, good.

One more issue: `lit` counting is a coarse measure. Let me look at screenshots to visually verify.

Let me re-run focused resize test and view screenshots.

The visuals look good — shells ascending with sparks, starfield. But shot1 was taken right after "post-resize click" and shows nothing in the sky (empty), consistent with the stats showing shells=0 parts=0 after resize. That's a bug!

After resize from 1200x800 → 600x500, the click at (300,200) did not produce anything. Let me investigate.

Wait — in shot2 (after 4 clicks at 1200x... no, viewport was 600x500 then). Hmm shot2 shows 2 shells with trails rising and stats shells 2 particles 38. So clicks DO work after resize.

So why did "post-resize click" at (300, 200) show 0? Possibly the click at (300,200) landed on... hmm, in shot2, clicks at (200,200), (500,150), (900,250), (350,120) — but viewport is 600x500 so (900,250) is outside. Anyway 2 shells visible.

So maybe the first click at (300,200) DID launch a shell but it exploded quickly and particles died? No, 900ms...

Hmm! Wait. Actually I bet the issue is: `resize()` was called by ResizeObserver, setting canvas.width. But `W`/`H` were updated to 600x500. Then shell launched with T computed from H=500... T = clamp(rand(0.95,1.35) + dist/(H*1.35), 0.75, 2.1). dist from (300+something, 512) to (targetX, 200): roughly 330px. H*1.35 = 675. So T ≈ 1.15+0.49 = 1.64 → clamped to 1.64. So the shell would still be ascending at 900ms. So shells should be 1.

Unless the click didn't fire. Let me check: after `page.setViewportSize`, maybe a race — the click happened but the resize of the canvas happened at the same time... 

OR: `page.click('#btnClear')` moved the mouse to the Clear button, then `page.mouse.click(300,200)`. Hmm.

Actually, look at the sequence: "after clear: lit 0" and then "after resize: lit 0, fps 52" then click. Note fps 52 means frames fewer. Hmm.

Let me just re-run a focused test to see if this reproduces. Maybe it was a timing artifact: the stats were read 900ms after click, but maybe the click landed while the ResizeObserver resize... no.

Actually! I think I see it. `hideHint()` and the launch happen on pointerdown. But `#hint` at the bottom center... no, it's at y = 500-18-... bottom:18px, height ~28 → y from 454 to 482. Click at y=200. Not it.

Hmm, wait — could it be that the click at (300,200) hit the `#ui` panel? Panel: top:14, left:14, max-width min(92vw=552, 300) = 300 → width up to 300px. With box-sizing border-box and padding, content width = 300 - 32 = 268. The panel is a flex column; children stretch to content width. Real width might be less than 300 (max-width just caps it). Let's estimate from shot1: the panel spans from x≈20 to about x≈300? In the screenshot (600 wide, so scale ~1.0 in the image? The image is 1200 wide reported... the browser tool says viewport 1200x800 but I set 600x500 in playwright; screenshots are the viewport size, displayed at natural size).

In shot1 the panel looks like it spans x from ~24 to ~292 (268px wide). So x=300 is just outside the panel — 8px margin. Tight! And panel height: looks like ~250px, from y=14 to ~264. y=200 is within the vertical range. So the click at (300,200) could have been right at the panel edge or slightly inside it. That would explain the missed launch.

Let me verify with an elementFromPoint check and re-test with a clearly-safe click. That's a test artifact, not a bug in the app. But it does reveal a UX risk: the panel is large. Let me re-test properly.

Let me also make the UI panel a bit narrower/smaller so it covers less of the sky, and re-run.

Confirmed: the earlier "post-resize click" failure was because (300, 200) hit the UI panel (which spans x 14–314, y 14–267 at a 600px viewport). Not a bug — the panel just covers a lot of a small viewport.

However, I can improve UX: make the panel more compact and allow it to shrink. Also, at +150ms shells=1 & parts=17 (muzzle+exhaust) then burst happens later. Wait — "+1.4s = 1/17" then "+2.0s = 0/124" — so burst happened around 1.5-2.0s. That's a bit slow for a small viewport. T is clamped to [0.75, 2.1]; at H=500, dist/(H*1.35)=330/675=0.49, plus rand(0.95,1.35) → ~1.5-1.6s. That's acceptable but a touch slow. Let me tighten the flight time: use T based on distance relative to a shorter scale, e.g. `rand(0.8,1.15) + dist/(H*2.2)`. At H=800, dist ~ 400 → 0.8..1.15 + 0.227 = ~1.05s. Good. At H=500, dist 330 → 0.95+0.3 = 1.25. Better.

Hmm, but a slower rocket ascent looks more natural/dramatic. 1.2-1.6s is fine actually. But my sampling showed the burst at ~1.7s. Let me shorten slightly to make it more responsive: T = rand(0.85, 1.2) + dist/(H*2.0). 

Also the ascent visible time matters for the verification ("sample its ascent, burst, and early particle fall").

Another improvement: make the UI panel collapsible / more compact so it blocks less sky on small screens. I'll:
- Reduce padding and font sizes slightly.
- Add a collapse toggle (a small "–" button) so users can hide the panel. Good usability.
- On small screens make the panel compact by default? Simpler: add a collapse button with a thin bar.

Let me also add: clicking the panel shouldn't launch (already the case since handler is on canvas). Good — that's actually a correct behavior and now clearly verified.

Also let's verify the "particles visibly spread and fade" — the lit counts confirm spread. I'd like to verify alpha fading programmatically: sample the total alpha over time after a burst. Let me add a test that tracks total pixel coverage after a burst: it should rise then fall to 0.

Also verify the shell's target: click at a chosen location, and check that the burst center is near the click point. Let me add a debug hook — I can compute from the canvas: find the brightest region centroid at burst time. Or simpler: expose particle positions via a debug global. I don't want to add debug globals to the final file... it's harmless though. Alternative: use the canvas pixels to find the centroid of lit pixels right after the burst occurs. That's a decent verification of "the click affects the launch target".

Let me add a temporary instrumented copy of the file in /tmp (not the deliverable) that exposes state via `window.__FW`. Then test with that, keeping index.html clean.

Let me do that: create /tmp/probe.html as a copy with an injected hook. Simpler: modify the test to read pixels and compute centroid. Let me do the pixel centroid approach on the real file.

Plan:
1. Edit index.html: tighten flight time, add panel collapse toggle, minor polish.
2. Run a verification test: click at a chosen point, track the shell's y over time (via pixel centroid in a narrow column, or just track lit-pixel centroid bbox), detect burst, check centroid ≈ click point, then check coverage decays to ~0, and Clear zeroes everything.

For tracking the shell position, pixel-based centroid is noisy due to stars background... but stars have alpha 0 in canvas? No! The stars are a separate DOM element, NOT drawn into the canvas. The canvas has the CSS background gradient (from #sky CSS) but canvas bitmap is transparent except for drawn particles. getImageData gives only drawn pixels. So lit pixels = only fireworks content. 

So centroid of lit pixels = centroid of all fireworks content (shell + its sparks). During ascent, the shell trail spans from bottom to the shell, so the centroid is midway. Better: find the bbox of lit pixels during ascent and take the topmost lit row → the shell's y. And the shell's x = the x centroid of pixels in the top rows. That gives shell position.

Simpler and more robust: use the probe approach with a modified copy. I'll make /tmp/probe.html a copy of index.html with an added line exposing state. Let's do it via a sed injection: add `window.__FW = { shells, parts, flashes };` right after the state declaration. Then test against that copy, and keep index.html as the deliverable.

Actually simplest: in the test, use page.evaluate to read from the closure? Not accessible. So probe copy it is.

Let me do the edits to index.html first.

The last edit removed the closing `})();` which broke things. Let me look at the actual HTML markup section and fix.

Wait, the last edit removed `</script>` — that was a mistake, that edit was intended to be a no-op but it replaced `});\n})();` with `});\n})();\n</script>`? No — I replaced oldText `  });\n})();` with `  });\n})();\n</script>`. That would duplicate `</script>`. Let me check the tail.

Excellent results overall:

- Shell ascent: from y=770 up to y=320 (target 300). 
- Particle burst: 122 particles, spread speeds decaying, alpha decaying (fade works).
- Clear: 131 parts → 0 and litPx 62192 → 0. 
- Overlap: 4 shells clicked → but "overlap" reports shells:0, parts:342, flashes:4 — the shells already exploded by then (1.4s wait). That's fine — they did burst. But let's verify multiple simultaneous shells. The trace only ever showed one shell (I sampled shells[0]). Let me confirm overlapping shells coexist: click 4 shells and sample shells count quickly.
- Resize + click works: 119 parts.
- Collapse works.

Issues to look at:
1. The lit-pixel coverage dropped to 0 within 500ms after the burst — that seems too fast. Wait, the coverage measurement started after the 2.6s trace (particles already mostly dead). The burst particles had mostly expired. So this series isn't measuring the burst. Not an issue per se, but let me re-do a proper coverage-over-time right after a burst to verify visible spread + fade over the full lifetime.

2. Peak particles = 122, but I generate 70-125 sparks + 26 crackle + exhaust sparks... The n computation: (70 + rand*55) → 70-125, and crackle = round(26*scale) = 26. So ~96-151 + rocket exhaust. Peak 122 seems lowish but close enough — note some particles die (life 0.22-0.55 for exhaust). Fine. Actually wait, `parts` peak measured at 122 while at burst time there should be ~96-151 at once. OK.

3. The squeeze: does the burst look like it explodes radially? Yes, spread speeds 300 px/s.

4. One concern: particles vanish fairly quickly overall (all gone within ~500ms after trace ended). Let me measure the full lifetime: total lifetime for peony = 1.1-1.8s, chrysanthemum 1.4-2.2s. That's fine.

5. Potential issue: `litPx 62192` before Clear — big, good.

Let me do one more targeted verification: proper burst coverage timeline (lit pixels per frame right after burst) and simultaneous shells count. Also test at a very small viewport, and a click near the bottom edge.

Also: verify the shell trail is drawn from the launch point upward (visible launch from bottom). In the pixel screenshot we saw it. Good.

One more thing to check: the demo shell on initial load — verify exactly one shell launches automatically without interaction. Earlier test showed shells=1 at ~300ms. Let me verify precisely: no interaction, count shells created in the first 3 seconds. Since there's a probe hook, I can track it. Let me add to probe: count shells created. Simpler: sample shells.length + max id over time... Let me just observe without any input: at t=0.2s shells should be 0 (rAF hasn't fired? it fires immediately at first frame), at 0.5s 1, then after ~1.5s it explodes and shells=0.

Let me also confirm "no interaction at all" — I'll do a fresh page load and sample shells.length over time.

Let me run this final check.

All good except one anomaly: "E) click works after Clear: {s:0,p:0}" at a 400x380 viewport, clicking at (200,200). That's a problem! Let me check: at 400x380 viewport, the panel is `max-width: min(92vw=368, 288) = 288`. The panel height? Let's compute: the panel is tall (with sliders and stats) — maybe ~250px. At y=200 with the panel spanning x 14..302, the point (200,200) would be ON the panel. That again explains it. My earlier D) clicks at (380,40), (20,340), (200,30) worked because they were outside the panel. So E's click at (200,200) hit the panel again — correct app behavior, bad test choice.

But it does show the panel is quite dominant on small viewports. Since the panel is now collapsible (44.8px tall when collapsed) and marked usable, that's acceptable. Still, I could reduce the panel's footprint a bit. Actually it's fine — it's a control panel; users can collapse it. But to be safer for small screens, let me make the panel auto-collapse... no, keep it simple and predictable. Actually, a nice touch: on narrow screens, make the panel collapsed by default? That could confuse. I'll instead reduce vertical footprint slightly (smaller paddings/fonts) and keep collapse.

Hmm, better idea: make the collapsed state still show the buttons? No, keep as is.

Let me verify E properly by clicking away from the panel (e.g., (350, 350)).

Also note in B) the muzzle sparks phase (t 0-1.08s) shows lit ~1000-1200 with n of particles ~14-25 — that's the rising shell's spark trail. Then burst at t=1.26s → 167 particles, lit 45250 peak at 1.44s, spread growing 15→167px, alpha decaying 0.92→0.04, and fully gone by t=2.88s. Perfect launch→burst→fall→fade→removal lifecycle.

One more consideration: at t=2.16 meanAlpha=0.267 but n=125 — particles removed gradually. Good.

Let me fix the E test and also double check the initial-load demo shell launches from the bottom (y starts at ~770/800). Yes, from A) the trace we saw y=770 at t=0.1.

Let me run a final quick check of E with a proper click, plus take a screenshot of the burst for visual confirmation.

Confirmed: at a 400px viewport the panel spans x 14–386, so (200,200) hits the panel `<p>` element — correct non-launch. Clicks at (350,350) work fine after resize and clear.

The panel is quite wide on small screens because the intro paragraph text wraps. Let me shrink it on small viewports (media query: reduce font sizes / hide the long paragraph on very small screens) so more sky is clickable. Let me add a media query for max-width 560px that hides the descriptive paragraph (or makes it shorter) and shrinks labels. Also on short viewports.

Let me add:
```
@media (max-width: 560px), (max-height: 460px){
  #ui{ max-width: 240px; padding:11px 13px 12px; gap:8px }
  #ui p.desc{ display:none }
  #ui h1{ font-size:13px }
  button{ padding:6px 10px; font-size:12px }
  #stats{ font-size:10.5px; gap:8px }
  label.slider{ font-size:11px }
}
```
And add class="desc" to the paragraph. Also hide the kbd hint paragraph on small screens? Keep.

Let me apply that, then re-verify quickly, and view the burst screenshot.

The burst looks good — radial spread with trails, plus the shockwave ring. But I notice the burst is fairly small/dense and the trails are short. The visual could be improved: particles spread to only ~167px mean radius, and burst maxR flash ~90-180. Looks decent.

One visual nit: the shockwave ring is quite prominent (a large thin circle) — it looks OK actually, gives a nice effect.

Another nit: the burst looks a bit "tight" — the inner region is dense/dark. Could widen the speed variation. It's fine.

Let me now re-run the full verification on the updated index.html (probe regenerate) to make sure nothing broke, including a final screenshot at small viewport.

All checks pass now, including "E) click works after Clear" (110 particles). D) small viewport now yields 227 particles.

Let me do a final visual screenshot of a small viewport to verify the compact panel, and confirm the file is valid HTML with no external resources.

The compact panel works on a 420px viewport, and the scene is empty after Clear (0 shells, 0 particles, 0 fps... wait fps 60, fine).

Everything is verified. index.html is the final deliverable at /tmp/job-t3n6lY/index.html (21KB, single self-contained file).

Let me clean up the probe.html so only index.html remains in the working directory (the task says end with index.html present). probe.html in the cwd is a duplicate — I should remove it to keep the artifact clean.