Matrix digital rain · mimo-v2.6-pro

Let me build the file.

Let me run it in the browser and check.

One concern: with trail fade using fillRect alpha 0.14, older frames fade — but that's per-frame fade, and pause should freeze. Good.

But note: drawColumn draws the whole trail each frame with its own alpha, plus the fade accumulates. That could double up. That's fine visually — actually drawing the full trail every frame plus fading creates a strong trail. Fine.

Another issue: glyphs array — needed computed as floor(headY/FONT_SIZE)+1 could be large if headY is negative... fine, clamped by trail.

Also `col.glyphs` grows as head moves down; when head is above the top (negative y), needed could be negative? floor(negative)+1 might be <= 0, so no glyphs added. Good.

Let's test in browser.

The effect looks decent — columns visible, brighter leading glyphs (white-ish glowing heads). Trails look a bit sparse/uneven, but acceptable. Actually there seem to be gaps in trails — some columns have long trails with gaps. The trail drawing with per-glyph alpha gradient plus fade... Fine.

Hmm, one issue: trails look fragmented because glyphs array only fills as head advances, and glyphs mutate. Actually the gaps come from drawColumn drawing cells at headIndex - ... which are contiguous. But fade alpha 0.14 with redraw of full trail each frame... The appearance is a bit patchy but it reads as matrix rain.

Wait — the fragmentation: some columns show scattered glyphs with gaps vertically. That's because the trail only spans `n` glyphs and I redraw them each frame at contiguous positions. So there shouldn't be gaps. Actually looking again, columns look mostly contiguous-ish but with variable brightness. Fine.

Let me sample at a later moment to check movement, then test pause and restart.

Columns are moving at different speeds (heads in different positions across frames), trails fade, leading glyphs are bright white/glowing. 

Hmm, one thing: trails look fragmented — glyphs appear scattered rather than continuous vertical streaks. Looking closer: some columns have gaps between glyphs. That's because the trail redraws each frame at contiguous cells... wait, the appearance shows gaps. Let me think: `needed = min(trail, floor(headY/FONT_SIZE)+1)` — glyphs array grows one per cell the head passes. But the head moves faster than one cell per frame sometimes; then needed jumps and multiple glyphs are added at once. So glyphs are contiguous. The gaps in the visual might just be the fade making lower-alpha glyphs nearly invisible against black, plus shadow. Actually looking at frame images, I see vertical runs of glyphs but also blank cells within a column...Actually wait — the fade approach: I draw the full trail each frame at full positions. So a column should show a continuous run of `n` glyphs from head upward. n is min(trail, cells passed). So the trail should be contiguous. The gaps I perceive are probably from columns overlapping / different columns interleaving in the visual field since CELL_W=18 equals FONT_SIZE=18 — adjacent columns are18px apart, and glyph width ~10px. Hmm, in the image columns look like they're at irregular horizontal positions... Actually the x positions look irregular because multiple columns... no, x is regular: i*18+9. But the screenshots show columns at irregular x spacing. Odd. Maybe some columns are dimmer so it looks irregular.

Hmm, but wait: some glyphs appear offset horizontally within a column. That's because ctx.fillText uses col.x - FONT_SIZE*0.5 as left x, which is consistent. But glyph widths vary slightly. Fine.

Actually I notice columns in the screenshot appear at x ≈ 35, 85, 115, 155, 235... irregular. Hmm. Maybe it's just my reading of the image. Whatever — it looks like Matrix rain and works. But could there be an issue where adjacent columns interleave? x = i*18+9 so spacing is 18px. In a 1200px wide image that's ~67 columns. The image shows maybe 25-30 visible column strips — but many are dim.

Hmm wait, but irregular spacing bothers me. Let me think again... Oh! I see: the visible "strips" might be groups of adjacent columns where some columns' glyphs are at different brightness. Fine.

Actually there IS a real issue: the trails show gaps because I mutate glyphs randomly and some positions... no.

Let me just move on to test pause and restart. Actually, one thing worth checking: after pause, the image must freeze exactly (no fading). Since I skip all drawing when paused, yes.

Test pause: click Pause, take two screenshots, compare pixel-identical-ish. Then resume, then restart and check trails cleared (frame should be mostly black briefly then fresh columns).

Also test resize. The browser tool likely has fixed 1200x800 viewport and no resize action. I can at least dispatch a resize via... there's no evaluate tool. Hmm. Browser actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. No evaluate. I can't easily resize the viewport. But I could verify resize logic by reasoning. Alternatively, key/type could type into... not useful.

Hmm, maybe I can use `browser` `key` to press... no. Resize verification: I can simulate by temporarily editing the code? Not real verification. I could run a headless check with node? No canvas. I'll just reason: resize() resizes canvas backing store, clears to black, rebuilds columns to cover width exactly (count = ceil(W/CELL_W)+1 columns at x = i*CELL_W + CELL_W/2, last one at ceil(W/18)*18+9 which is past the right edge by up to 27px — actually covers the right edge since the previous one at (ceil(W/18)-1)*18+9 which is >= W-18+9 = W-9... hmm, x is the glyph center? I draw at col.x - FONT_SIZE*0.5 as the text left. So text spans [x-9, x+9] roughly. Column i covers [i*18, i*18+18]. For i = ceil(W/18)-1, it covers up to ceil(W/18)*18 >= W. So full coverage. Good — no uncovered strip.

Height: columns start anywhere along the height so no blank strip vertically at init after resize. But after resize, existing on-screen content is cleared and columns respawn everywhere — acceptable ("without stretching an old screenshot"). Good.

Now test pause.

Paused. Now take two motion frames to verify the image is frozen.

Frozen across 1.6 seconds. Now test Restart — but first resume, run a bit, then click Restart and check that trails are cleared (image should be black-ish with fresh columns starting from top / spread).

Actually to check "Restart clears previous trails", I should click Restart while paused or running? The requirement: "Restart resets the columns and clears previous trails." I'll click Restart right now while paused — then the canvas should be fully black (since paused, no drawing happens after clear). That's a good check of trail clearing. Then resume and check fresh rain falls.

But careful: my restart while paused clears and rebuilds but draws nothing → black screen while paused. Then resume shows fresh rain. That's acceptable behavior... though some might expect restart to show something. The verify statement says "use Restart and check that old trails are cleared" — a black screen immediately after restart proves it. But better UX: after restart, draw the initial state? Hmm, if paused and restart leaves a fully black screen, that might look like a bug. Maybe restart should also render one frame of the fresh columns so the user sees new rain start? Actually the requirement says restart "resets the columns and clears previous trails" — a blank canvas momentarily is exactly "old trails cleared". But leaving it blank while paused is odd.

Better: on restart, if paused, draw one static frame of the fresh columns (which won't accumulate old trails). That keeps it non-blank while still clearing old trails. But then "check that old trails are cleared" would show fresh columns with short trails — visible proof. I think drawing one fresh frame is nicer. But it also could confuse the check that old trails are gone... no, fresh columns start with heads spread and only tiny trails drawn. Hmm, but with spawnAnywhere on restart, columns would look immediately populated — like a jump-cut, similar to initial load. That's fine and matches "resets the columns".

Actually wait — on restart with spawnAnywhere, columns are spread across the screen with trail arrays empty, so a single draw would show just single bright glyphs per column (n=0 glyphs until update runs). Actually glyphs array is empty so nothing draws until update adds glyphs. Hmm, so one draw would render black too.

Simplest: on restart, force one update+draw step so trails begin to form? That would still be nearly black.

I think the cleanest semantic: restart clears everything and starts the rain fresh (like a reload). If paused, keep it paused (black canvas with "Paused (restarted)" status). If running, rain restarts from scratch. The verification "old trails are cleared" is satisfied.

But a black screen while paused-restart might be perceived as broken. Alternative: restart resumes to running? No — spec says pause freezes; restart resets. Keeping play state is reasonable, but leaving a blank frozen screen is weird.

Compromise: on restart while paused, draw one frame after performing a single small update so you see fresh columns beginning (short trails), which is clearly "reset" not "frozen old image". Let me implement: in restart handler, clearTrails(); buildColumns(true); then advance simulation by a fixed small step (e.g., 1 frame of dt=1/60) and draw once — so a paused user sees the fresh start state instead of pure black. Actually simpler: run updateColumn with dt=0.5 and draw once — giving short trails of a few glyphs.

Hmm, but then "old trails cleared" check would show a screen with short fresh trails — good visual proof actually.

Let me do that: after reset, if paused, simulate ~0.6s of movement and draw once.

Actually careful: updateColumn with dt=0.6 and then draw gives trails of maybe ~3-8 glyphs per column. That looks like a fresh start. Good.

Let me implement that, then verify restart while paused shows cleared/fresh state, then resume and verify motion continues.

Also I should double check: when resumed after restart, lastTime=0 forces dt=0 on first frame — good.

Let me edit.

Wait — buildColumns(true) spawns heads anywhere along the height with empty glyph arrays; updateColumn with dt=0.6 moves head down 0.6*speed and fills trail up to min(trail, floor(headY/FONT_SIZE)+1). So for columns whose head is already well down the screen, the whole trail fills in one go — that would draw long trails immediately, defeating "old trails cleared"? No — these are brand new trails, so old trails are still cleared. It looks like an instant reset to a full rain state, similar to the initial load. Acceptable.

Hmm, but a cleaner "restart" feel: heads all spawn near the top so you see the rain begin. The spec says "Vary column speed and start position" and "Restart resets the columns and clears previous trails." Spawning spread out is fine, matches initial load. But for restart specifically, it might be nicer for columns to start at the top so it visually reads "restarted". However if all start at top, the first ~1 second is a mostly-empty screen. Requirement says restart "resets the columns and clears previous trails" — a mostly empty screen right after restart IS the check. I'll make restart spawn columns at the top (spawnAnywhere = false) so trails visibly start fresh and old trails clearly gone. That gives a clear verification: right after restart, screen nearly black with rain starting from the top.

But with spawnAnywhere=false, heads spawn at -rand(0,6)*FONT_SIZE - trail*FONT_SIZE*rand(0.2,1), which could be very far above (up to 28*18 = 504px above) — leading to slow visual startup. Let me use a dedicated spawn: heads staggered in a band just above the top, e.g. headY = rand(-8*FONT_SIZE, 0). And with the paused draw step of 0.6s they move down a bit.

Let me restructure: makeColumn(index, mode) where mode is 'scatter' | 'top'. For restart use 'top' with headY = rand(-10*FONT_SIZE, -FONT_SIZE). Then trails only appear where heads have passed → mostly black right after restart. 

Also recycle after leaving bottom keeps current behavior (spawn above top) — good.

Let me implement mode.

Wait: recycle mode "recycle" falls to the else branch which is same as old behavior. Good.

Also on restart while paused, the draw step of 0.6s moves heads down but they start above the top so only a few glyphs show — perfect: black canvas with fresh short trails.

Now reload and test restart. Currently the page is paused with old code. Reload resets to running. Plan:
1. Reload → screenshot (fresh).
2. Let it run a few seconds (motion) to accumulate trails.
3. Click Restart while running → screenshot: old trails cleared, rain restarts from top.
4. Also test restart while paused.
5. Resume and check motion continues.

Let me do it.

Fresh load works. Now let it run a couple of seconds (motion), then click Restart and check old trails are cleared.

Actually motion runs 4 frames over ~2s; then click restart. Let me just wait via motion then click restart.

Trails have built up nicely — long fading trails visible. Now click Restart and screenshot immediately to verify trails are cleared.

Old trails are completely cleared — canvas is black immediately after restart. Now verify rain restarts fresh from the top and continues.

Rain restarts from the top and regrows over time. 

Now test: restart while paused (should show a fresh frame, not blank), then resume continues. Also test resize — I can't change viewport with the browser tool... but maybe I can verify the resize handler by triggering a window resize. No evaluate. Hmm.

Alternative for resize check: I could use `browser` `key` to... no. Or check via `inspect` DOM? Inspect gives DOM snapshot but not computed layout. It might show element info. Let me try clicking Pause then Restart to check the paused-restart frame, and then use inspect to see DOM info. Maybe inspect includes viewport info? Unknown.

For resize, another idea: I can make the page itself respond to something... no. I'll verify resize logic by code review plus check the canvas covers the viewport exactly at 1200x800 (inspect DOM for canvas width/height attributes). If window.innerWidth=1200, canvas.width should be 1200*dpr. Let me inspect.

Let me do pause → restart → screenshot, then resume → motion to confirm it continues.

Now paused. Click Restart while paused and check the fresh frame (short trails near the top, old trails gone).

Restart while paused: old trails cleared, fresh short trails entering from the top, and the image is frozen (paused). 

Now resume and verify it continues.

Then verify resize. Can I trigger a resize? Maybe the browser tool's viewport is fixed at 1200x800. I can't resize. However, I can verify the resize handler correctness via code review, and verify the canvas covers the viewport exactly by inspecting DOM (canvas width/height attributes vs viewport). Let me use `browser` `inspect` to see DOM details.

Actually another way to test resize logic without a real resize: the `resize()` function is also invoked on load. Testing an actual resize would need window resize. Perhaps the browser tool resizes if... no such param. I'll rely on code reasoning and note resize as unverified at runtime.

Hmm, but maybe I can indirectly test: zoom? Press key combos like Ctrl+-? The browser tool `key` action sends keys to the page. Browser zoom might trigger resize... but that's within the sandboxed iframe; zoom would change innerWidth. That could actually trigger the resize handler! Let me try: press "Control+-" or "Control+=". Risky — might change tool screenshots resolution. Actually it would just be CSS zoom of the page; window.innerWidth would change and my handler would rebuild. Then screenshot to check coverage. But zoom may not be supported in headless via key events.

Alternatively: `key` with "F11"? no.

Let me try a simpler approach: verify via inspect that canvas attribute sizes match innerWidth/innerHeight * dpr so no stretch/strip at current size, and reason about resize. I have limited time (~5 min used). Let me do resume + motion check and inspect, then wrap up.

Actually, I can genuinely test resize: temporarily modify... no, better use of time is verifying resume works and canvas sizing.

Let me try key Control+= zoom attempt quickly? If the sandbox doesn't respond, no harm. Actually browser zoom keys in headless Chrome via CDP dispatchKeyEvent usually do trigger zoom in the page. Let's try "Control+Minus" then screenshot, then "Control+0" to reset. If innerWidth changes, my resize handler rebuilds columns — screenshot would show a smaller logical viewport scaled up, still covering fully (no black strip, no stretched old image since we clear and redraw). That's a decent test.

Let me first resume and confirm motion continues.

Resumed. Now verify the animation continues (motion). And I want to test resize. Let me try browser zoom keys to force a window resize event: press "Control+-". Actually in a sandboxed iframe the key may go to the page. Let's attempt it — if zoom changes innerWidth, my resize handler runs and we can see if the canvas still covers the full viewport with no black strip and no stale stretched image.

Let me do motion first to confirm continue, then try zoom.

Animation continues after resume. Now try to exercise the resize path via zoom keys. Press "Control+Minus" via browser key.

Actually, in many of these harnesses `key` accepts a key name like "Control+-" or just "-" with modifiers unclear. Let me try text "Control+-"? The spec: "key": key to press. I'll try "Control+-".

Risk: if the harness intercepts, nothing happens. Let's try.

Hmm — the screenshot still shows 1200x800 but the glyphs now appear smaller/denser? Actually the columns look denser than before... Hard to say. The zoom may not have changed anything. Let me inspect the DOM to see canvas width/height attributes and the button text size to determine if zoom changed innerWidth.

Actually, I notice the rain now appears to fill more columns (denser) — the earlier screenshots after restart had columns at 18px spacing too. Hmm, could be zoom changed innerWidth to larger (zoom out → innerWidth larger → more columns → resize handler ran). The image shows more columns than before? Comparing frame density... The last screenshots look similar density.

Let me use `inspect` to check DOM state.

The inspect action returned only a screenshot (no DOM dump). The visuals still fill the entire 1200×800 frame edge-to-edge — no black strip on any side, and the UI scaled the same, so zoom likely didn't change (or resize handled it fine).

Note the buttons render at same size, so zoom didn't apply. I can't force a window resize with the available actions. However, I can verify the resize path indirectly: I could write a tiny self-test... but no evaluation either.

One more idea to exercise resize: dispatch a resize event from within the page itself — e.g., temporarily add code? No. But I could use `type` into... there are no inputs.

Alternative: I can make the page listen to a keyboard shortcut that calls resize() manually — but that's not a real resize test either. Actually — a real resize IS what matters: canvas.width/height + style + column rebuild. I can simulate the essential effect of a resize by having the code path be the same `resize()` used at load. At load it clearly worked (canvas covers exactly the viewport, columns cover the width).

To be more rigorous cheaply: add a hidden dev shortcut? Not needed for the deliverable. But I could verify resize handling headlessly with node? No canvas in node.

Actually — one trick: the browser harness `key` might support "F11"? Not useful either.

Better trick: I can force an actual resize by testing with a temporary test harness page? The requirement says end with index.html present. I could create a temporary second file test.html? The instructions say "write it ALL into one self-contained file named index.html" — extra files are discouraged but the final requirement is index.html present. I'd rather not.

Actually, there IS a way: browser zoom via "Control+-" didn't change anything visible. Let me try keyboard "Control+Shift+-"? Meh.

Hmm, what about the possibility the harness runs index.html in an iframe whose size is fixed. A resize event could be triggered by devtools... unavailable.

I'll accept resize as verified by code review + initial-load behavior (same code path), and note it. Actually wait — I can partially verify: window resize handler exists and calls resize(); resize() is the same function verified at load. The risk of "stretching an old screenshot" is avoided because we clear with fillRect and rebuild; the risk of "uncovered strip" is avoided because count = ceil(W/CELL_W)+1 columns cover W and the canvas backing store is resized to viewport * dpr.

One more real check I can do: the mouse... no.

Let me spend remaining effort on a robustness detail: `window.innerWidth` includes scrollbar? overflow hidden so no scrollbars. Good.

Another detail: on resize while paused, we clear and rebuild columns with "scatter" mode, but we don't draw anything → black screen while paused after resize. Similar to the restart-while-paused issue. Should paint a fresh frame when paused, like restart does. Let me extract a helper `paintStaticStartFrame()` used by both restart (mode "restart") and resize (mode... resize uses scatter with heads already on screen — a single draw would show nothing since glyph arrays are empty; the update step of 0.6 fills trails). Let me refactor: after buildColumns in resize, if paused (or even always for first paint), run the same step+draw. Actually for resize while running, the next frame will draw anyway (fade overlay on cleared black — fine). For paused, do the step+draw.

Implement helper:

function paintFreshFrame(mode, step) {
  clearTrails();
  buildColumns(mode);
  for (...) updateColumn(col, step, i);
  for (...) drawColumn(col);
}

But resize must also resize the canvas first. Let me just add the paused branch in resize() and reuse a shared function `stepAndDraw(dt)`.

Let me edit: add function stepAndDraw(dt) that loops update+draw; use it in restart handler and in resize when paused. And in the restart handler replace inline loops.

Also in `frame()` the loops could use it, but keep as is (fine).

Let me apply the edit and then do a final verification pass (reload, motion, pause, resume). Also double-check that resize() call at load draws... at load, paused=false and rAF will draw next frame — fine.

Then final check in browser.

Wait: `resize()` is called on load before `paused` is defined? Order: variables declared at top (paused = false), resize() called at bottom. Fine. But resize() is defined before stepAndDraw — function declarations are hoisted, fine.

Also `buildColumns("scatter")` in resize: mode "scatter". Good.

Now reload and do final verification pass. Also try one more resize attempt: maybe `browser` `key` "Control+0"? Not needed.

Actually, here's a genuine resize test I can do: open index.html via file URL in the harness — no. Skip; note as unverified at runtime.

Hmm, wait — actually I could verify resize at runtime using a trick: my keyboard handler intercepts Space and R. What if I add no test hooks... Fine.

Actually, one legit approach: `browser` `type` action types text into focused element. If I focus the body and type... no resize.

OK final verification: reload → motion → pause → screenshot → resume → motion. Keep it brief given the time budget.

Wait — this looks denser than before! Now there are many more columns. Did the zoom change innerWidth? Or... hmm. Compare to earlier: earlier frames had ~25-30 visible column groups; now there appear to be more, with18px spacing... Actually earlier frames also had many. Hard to compare. The layout spans full width edge-to-edge in all cases. 

Hmm, one thing: earlier, columns looked like they were spaced ~18px with dim ones between. Now it looks similar but with brighter overall content because scatter mode fills everything initially. Fine.

Now: motion → pause → check frozen → resume → motion → restart check. Actually I already verified those flows with the previous code; the refactored code only changed the paused-paint helper. Let me do a quick pause + restart check with new code and resume.

Paused. Now Restart while paused with new code — expect fresh frame with short trails from top.

Works: old trails cleared, fresh short trails entering from the top, frozen while paused. Now resume and confirm it continues — quick motion check. Then done.

Immediately after resume (right after restart), the canvas shows the restarted state and it should be falling again. The screenshot is one instant — trails are still short since restart was recent. Let me do one motion to confirm it grows/moves.

Everything works: independent columns, bright leading glyphs (white glowing), fading trails, recycling, pause/resume, restart clearing trails. Full-viewport coverage in all frames.

Resize: I couldn't force a real window resize with the available browser actions (no viewport/resize control; zoom keys had no effect). The resize path (resize()) is the same function exercised at load, and the column rebuild covers the width exactly. I'll note it as unverified at runtime.

Final: confirm file exists in cwd. Let me quickly list and maybe validate syntax with node --check on the extracted script? Quick sanity: file written fine and it ran without console errors (only sandbox warning). Good enough.

Let me do a quick ls to confirm index.html is the only artifact.

index.html is present, self-contained, no external references. Done. Report.