Drum machine · mimo-v2.6-pro

Let me build the app. Single file index.html.

Key design: Web Audio scheduler with lookahead (setInterval 25ms, scheduleAheadTime 0.1s). Steps are 16th notes: secondsPerStep = 60/bpm/4.

Voices:
- Kick: sine oscillator with frequency ramp 150->50, gain envelope.
- Snare: noise burst through bandpass + a triangle oscillator body.
- Hi-hat: noise through highpass with short envelope.
- Clap: noise burst with multiple quick bursts (3 bursts) through bandpass.

Noise buffer created once.

Audio unlock: AudioContext created/resumed on first user gesture (Play button click). Also show a hint overlay? Keep simple: an "Unlock Audio" indicator that changes; context resume on any pointerdown.

UI: grid with 4 rows x 16 steps, buttons. Step numbers header. Current step highlight. BPM slider 60-180 with number display, and maybe a number input. Play, Stop, Clear buttons.

Editing during playback: pattern is read at schedule time from the pattern array, so edits affect playback immediately without duplicate sequences. BPM read at schedule time too — but changing BPM mid-playback: recompute step duration; to handle cleanly, when BPM changes, adjust nextNoteTime based on new step duration from current position? Simplest: store currentStep and nextNoteTime; on BPM change, set nextNoteTime = max(nextNoteTime, currentTime + small) ... Actually if we just use new secondsPerStep for subsequent scheduling, there may be a gap or overlap. Fine approach: keep `nextNoteTime` and when BPM changes, adjust: nextNoteTime = lastScheduledTime? Let's do: keep track of `nextNoteTime`; on BPM change, set nextNoteTime = Math.max(ctx.currentTime, nextNoteTime) but change duration for future. There could be a slight hiccup but acceptable. Better: maintain `nextNoteTime` relative to the anchor. Let me just do: on bpm change during playback, set nextNoteTime = Math.min(nextNoteTime, ctx.currentTime + newDur) — hmm, actually a common approach: schedule based on absolute time computed from start time and accumulated steps... but variable BPM complicates.

Simplest robust: each time we schedule a step, nextNoteTime += currentStepDur. On BPM change, clamp nextNoteTime = Math.max(ctx.currentTime + 0.02, ...) no — if BPM increases, nextNoteTime is already fixed and we just wait that long; then subsequent steps use faster timing. That's acceptable and safe. Actually to make the change feel responsive, clamp: nextNoteTime = Math.min(nextNoteTime, ctx.currentTime + newStepDur). That ensures no more than one step of gap. I'll do that.

Playhead highlight: use requestAnimationFrame to compute which step is "current" based on scheduled times. Keep a queue of {step, time} and pop when audio currentTime >= time. Highlight that step.

Stop: clear timer, clear queue, reset currentStep=0, nextNoteTime=0, playhead to step 0 (highlight first step? "resets the playhead to the first step" — show highlight on step 1 as next-play position maybe). I'll show a "next step" indicator. On stop, highlight step 0.

Let me write it with nice styling: dark theme, grid with 16 columns, accent color per row.

Visual: rows labeled with names and colored dots, mute? Not required. Keep steps toggleable.

Also verify with browser tool.

Let me write the code.

Scheduler:
```js
let isPlaying=false, currentStep=0, nextNoteTime=0, timerId=null;
const LOOKAHEAD=0.1, INTERVAL=25;
function scheduler(){
  while(nextNoteTime < ctx.currentTime + LOOKAHEAD){
    scheduleStep(currentStep, nextNoteTime);
    stepQueue.push({step:currentStep, time:nextNoteTime});
    nextNoteTime += stepDur();
    currentStep = (currentStep+1)%16;
  }
}
```

scheduleStep: for each row, if pattern[row][step], play voice at time.

Voices functions with (time) param.

kick:
```js
function kick(t){
  const o=ctx.createOscillator(), g=ctx.createGain();
  o.type='sine';
  o.frequency.setValueAtTime(150,t);
  o.frequency.exponentialRampToValueAtTime(45,t+0.12);
  g.gain.setValueAtTime(0.0001,t);
  g.gain.exponentialRampToValueAtTime(1.0,t+0.002);
  g.gain.exponentialRampToValueAtTime(0.0001,t+0.4);
  o.connect(g).connect(master);
  o.start(t); o.stop(t+0.45);
}
```
Note: connect returns node so chaining works.

snare:
```js
function snare(t){
  // noise
  const src=ctx.createBufferSource(); src.buffer=noiseBuffer;
  const bp=ctx.createBiquadFilter(); bp.type='bandpass'; bp.frequency.value=1800; bp.Q.value=0.8;
  const g=ctx.createGain();
  g.gain.setValueAtTime(0.0001,t); g.gain.exponentialRampToValueAtTime(0.8,t+0.002); g.gain.exponentialRampToValueAtTime(0.0001,t+0.18);
  src.connect(bp).connect(g).connect(master);
  src.start(t); src.stop(t+0.2);
  // body
  const o=ctx.createOscillator(); o.type='triangle';
  o.frequency.setValueAtTime(185,t); o.frequency.exponentialRampToValueAtTime(120,t+0.1);
  const og=ctx.createGain();
  og.gain.setValueAtTime(0.0001,t); og.gain.exponentialRampToValueAtTime(0.5,t+0.002); og.gain.exponentialRampToValueAtTime(0.0001,t+0.12);
  o.connect(og).connect(master); o.start(t); o.stop(t+0.15);
}
```

hihat: noise -> highpass 7000 -> gain env 0.05 decay. Add slight metallic: two square oscillators? Keep noise-based.

clap: noise -> bandpass 1200 Q 1.2, envelope with 3 bursts using setValueAtTime/linear ramps at t, t+0.012, t+0.024 then decay to 0.2s.

Master: gain 0.8 -> destination. Maybe a compressor to avoid clipping. Use DynamicsCompressor.

Noise buffer: 2 seconds white noise, created at ctx init.

Audio unlock: create ctx lazily in `ensureAudio()` called on any user gesture (pointerdown on document once). Show status text "Audio: locked/unlocked".

Now write the file.

Grid layout: CSS grid, 16 columns. Steps grouped in 4s (beats) — add margin after every 4th step. Use `.step:nth-child(4n+1){margin-left}`... simpler: grid-template-columns: repeat(16, 1fr) and add border-left on 5th/9th/13th.

Row label column on left.

BPM control: range input + number readout. Also allow arrow keys, fine.

Pattern initial:
kick: steps 0, 8 (+ maybe 10)
snare: 4, 12
hihat: every even step (0,2,4,...) or all 16? Let's do every 2nd step plus a couple: 0,2,4,6,8,10,12,14.
clap: 4, 12 (alongside snare) — or 12 only. Let's do clap at 4 and 12.

Actually let's make it slightly more interesting: kick 0,6,8; snare 4,12; hat even; clap 4,12? Clap layered with snare is fine.

Now writing. Also keyboard: space to play/stop? Optional but nice. Careful not to interfere with buttons. I'll add space toggles play/stop.

Playhead rendering: rAF loop updates classes. Track `queue` of {step,time}; in rAF: while(queue.length && queue[0].time <= ctx.currentTime) { currentVisual = queue.shift().step; } set class.

Also "next step" indicator during playback? Just highlight current step (the one sounding) plus playhead column line. I'll highlight the sounding step in all rows (column highlight) and add `.playing` class on the column via data attributes.

Implementation: each step button has data-step index. In render: document.querySelectorAll('[data-step="i"]').forEach(...). Fine for 64 elements.

Let me write it.

Also on stop, reset highlight to step 0.

Edge: When not playing, no highlight of "current step"? Requirement says stop resets playhead to first step — so highlight step 0 when stopped. Do that.

Write file now.

For clear: set all pattern false, update UI.

Toggle step: pattern[row][step] = !... ; update UI. Reads at schedule time so affects playback.

Now the code.

Let me also guard: `if(!isPlaying) return` in scheduler.

play(): ensureAudio; if ctx.state === 'suspended' await resume. Then isPlaying=true; currentStep=0; nextNoteTime = ctx.currentTime + 0.06; stepQueue=[]; timerId=setInterval(scheduler,25); scheduler() immediately; start rAF.

Stop(): clearInterval; isPlaying=false; stepQueue=[]; currentStep=0; visual step 0.

Should stop cancel future hits? "Stop cancels future hits" — since we schedule ~0.1s ahead, there may be already-scheduled oscillators. To cancel, track scheduled nodes in an array and stop them at stop time. I'll keep `activeNodes` list and on stop call node.stop(0) / disconnect. Let's do: push each source node to `activeNodes` array, and on stop, iterate and try stop(ctx.currentTime) catch. Also remove on ended. Simple: keep array, on stop: for each n try n.stop() catch; then clear array. Also prune array in scheduler to avoid growth: filter nodes that ended — track endTime. I'll add {node, endTime} entries and prune when ctx.currentTime > endTime.

OK. Write.

CSS: dark bg #12141a, cards, accent colors: kick #ff5c5c? Use per-row hue. Steps: rounded 8px, height ~44px. Active (enabled) filled with color gradient, glowing. Current step column: outline/brightness.

Let me write the full file now.

Also add a "status" line showing "Step 1/16 · BPM". Nice.

Time budget: write file, run browser checks.

One more detail: stepDur = 60/bpm/4 seconds.

Let me produce the HTML.

Now run in browser and check.

One concern: `--c` used with color-mix in CSS; color-mix support should be fine in modern Chromium. Let's check.

Also the overlay covers the app until unlocked — clicking "Enable Audio" unlocks. But the overlay may block interaction; user clicks Enable Audio, ctx resumes -> updateAudioState hides overlay. Good. But if ctx state isn't running yet... resume() promise then updateAudioState. Fine.

Actually potential issue: clicking a step calls ensureAudio() but overlay blocks clicks anyway.

Let's run browser.

Initial output looks good. Pattern shows 16 active steps — kick 3, snare 2, hat 8, clap 2 = 15. Hmm, it says 16. Let me count hat: [1,0,1,0, 1,0,1,0, 1,0,1,0, 1,0,1,1] = 8 ones (positions 0,2,4,6,8,10,12,14,15?) Let's count: 1,0,1,0 =2; 1,0,1,0=2 (4); 1,0,1,0=2 (6); 1,0,1,1=3 (9). So hat=9. kick=3, snare=2, clap=2 → 16. Correct.

Now click Enable Audio and test playback.

Audio unlocked, overlay hidden, playhead on step 1 (highlighted). Grid looks good. Label "HI-HAT" wraps to two lines — minor. I could reduce label font or use white-space nowrap. Let's fix that quickly later.

Now click Play and observe playhead advancing via motion frames.

Playing state set. Now check motion to confirm playhead advances.

Playhead advances across the grid (steps 5, 10, 14, then wrapped to 3) — wrapping works and the highlight column moves. The enabled steps flash white when hit (visible at step 5 frame: snare/hat/clap brightened).

Now test BPM change while playing. Set slider to 180 via keyboard on the slider? The browser tool click on slider would jump thumb. Let me click the slider handle and press arrow keys, or click at position near right. Range input: clicking sets value to that position. Clicking at x≈973 (right end) sets ~180.

Let me click on the slider near the right end to raise BPM, then check "Step length" readout shows ~83 ms and that playback speeds up.

Slider is at x from760 to 975 approximately (width 220px). Clicking at 970 → value ~178.

Then verify position advances faster via motion.

Also test: toggle a step (e.g., kick step 3) and check pattern count changes and the step is on.

Then Stop → check position 1/16 and pattern retained. Then Play again → restart from1.

Then Clear → all off.

Let me do the BPM change first.

BPM now 180, step length 83 ms, playback continues (position advanced5→3 in DOM capture, wrapping). Good.

Now toggle a step: click kick step 3 (empty cell at x=353,y=243). Check "Pattern 17 active steps" and cell becomes on.

Then verify it sounds — can't hear, but visual flash appears. I can verify programmatically that trigger is called by checking... well, we can rely on visual flash. Let's click and inspect DOM for `.on` class on that step.

Kick step 3 is now on (red at step 3), active steps 16→17. Live editing works while playing.

Now Stop and verify playhead resets to 1/16 and pattern retained (17 steps). Then Play again and confirm start from step 1.

Also I noticed the "HI-HAT" label wraps. Fix: reduce font-size or add white-space:nowrap on .name. Let's fix after tests.

Also verify no console errors — so far only sandbox warning.

Now Stop.

Stop worked: Position 1/16, playhead highlight on step 1, pattern retained (17 steps, kick step 3 still on). Now Play again and confirm start from step 1, and no duplicate/double-speed sequencing (i.e., playhead advances one step at a time).

Let me press Play and then check motion briefly to see only one column highlighted (no duplicates) and starting at 1.

Also test Clear afterwards.

Restarted from Position 1/16 with pattern retained (kick step 3 on). Now check motion for single playhead, then test Clear.

Let me inspect DOM programmatically? The browser tool's "inspect" gives DOM. I'll do a motion capture to see only one column highlighted.

Then Clear test.

Only one highlighted column at a time — no duplicate sequences. Frames show step 8, 15, 6, 13 — advancing by1 step at a time (a bit fast at 180bpm, and the frames show correct positions). Good.

Now test Clear while playing: expect all steps off and playback continues silently (no hits). Then Stop. Also verify after Clear, restart uses empty pattern — well, "Starting again uses the currently displayed pattern" is satisfied since pattern array is the source.

Also fix the HI-HAT label wrapping.

Let me click Clear.

Clear works: 0 active steps, all steps show as off (with colored borders from a flash? Actually the cells show colored outlines — those are the `.flash` hit animation leftovers? No — the `.hit` flash is a white overlay. The colored outlines look like the `.pip` is showing... Hmm the screenshot shows cells with colored borders on the pattern positions. That may be the flash animation fading out at the moment Clear happened... no, the cells are off now.

Wait: look closer — kick step 1,3,7,9 have colored (red) borders, hat steps have blue borders. These are the previously-on steps. Why would `.step` off have colored border? Because `renderPattern` removes `.on`... but border-color of `.step` is `#333b4e`. Hmm, could this be a lingering `flash` class (white `.hit` overlay) — no, that's white overlay not border.

Actually it might be the browser's screenshot rendering of the transition mid-way: background transitions from color to gray over .1s and border-color transitions over .1s too. The screenshot was captured within the transition period (Frame1, +0ms). That's likely. Fine.

Also note the pip dot shows at center on those cells — `.step .pip` opacity is 0 unless `.on`. In the image, pips appear visible as dark dots... that's just transition again.

Not a real problem. Let me verify after a moment the cells render cleanly, and also fix the HI-HAT label wrap.

Let me apply the label fix (white-space: nowrap, smaller font) and then re-check.

Also check console for errors — only the sandbox warning so far. Good.

Fix CSS: .track-label .name{white-space:nowrap; font-size:12.5px} and reduce padding. And maybe hide hint on narrow. The label column is 108px; "HI-HAT" at 13px bold with letter-spacing .9 plus dot 11px + gaps 9px + hint "HI". Tight. I'll reduce name font to 12px and letter-spacing .5, and hint font9px.

Let me edit.

Now reload and re-verify: initial state, labels don't wrap, and a quick end-to-end retest (toggle + play + stop). Also confirm no console errors after reload.

Also I want to double-check one behavior: pressing Play twice shouldn't create duplicate sequences — `start()` returns early if isPlaying. Good. But clicking Play while playing also calls ensureAudio and resume → fine.

Another edge: the `stateWatcher` interval sets ctx.onstatechange — harmless.

Let me reload and run the verification pass again briefly.

Reset to initial state with the audio overlay again. Now click Enable Audio, then Play, then verify labels not wrapping and run quick toggle/stop checks.

Let me do: click Enable Audio (600,462), then screenshot.

"HI-HAT" now fits on one line. Good.

Final quick check: toggle a step (snare step 9, empty at x=685, y=300), then Play, then Stop — confirm restart from 1 and pattern retained. Let me combine: click snare step 9 → count 17; Play; motion; Stop.

Actually I already verified these behaviors before the CSS-only change. But the instruction says recheck affected behavior after fixes. The change was CSS-only, but a quick play/stop pass is cheap. Let me do a fast pass: click step toggle, Play, motion, Stop.

Snare step 9 toggled on (17 active). Now Play + motion + Stop.

Playing, started at Position 1/16 with the edited pattern. Now Stop to confirm reset, then done.

Also I could verify audio is actually being produced — no way to hear, but I can check that AudioContext currentTime advances and that no errors were thrown in console. Console shows no errors. I could additionally verify via a quick evaluate... The browser tool has no evaluate action. Fine.

Let me press Stop and take final screenshot, then check console.

Everything works. No console errors (only the sandbox iframe warning, which comes from the harness, not the app).

Final check: file exists and is self-contained (no external refs). Quick grep for http/cdn.

No external references. File present. Done.

Report briefly what was checked and what remains unverified.