Mandelbrot explorer · qwen3.8-27b

Build a single-file Mandelbrot explorer. Use a Web Worker? No, workers via blob are allowed (no network needed). But more simply: chunked rendering via requestIdleCallback / setTimeout to keep responsive. Render to ImageData, do it row by row, split into chunks with setTimeout to keep the UI responsive.

Implementation plan:
- Full-screen canvas, wheel zooms at cursor position, drag to pan.
- Smooth coloring: nu = n - log2(log2(|z|))
- Color palette is a procedural gradient (sine-based).
- Interior points get a distinctive color (e.g. black, or a dark color).
- A reset button, a zoom indicator if needed.
- preventDefault on the wheel.
- Re-render on navigation; for responsiveness, render in chunks (row batches) with rAF or setTimeout.

Write it, test in the browser, take a screenshot.

Bug check: inside computeRow I referenced `job.zoomPhase`, but it's not set — no problem (undefined → 0). However, the palette doesn't shift with zoom; still, acceptable — color bands appear from the nu cycle. Actually, a constant phase is fine; the zoom-linked shift is omitted. Also the box test radius 256: escape radius² = 65536, nu computation is fine.

One concern: `Math.log2(mag)` when mag < 1 is a negative value, no problem.

Note: the nu formula: standard is n + 1 - log2(log2|z|). I wrote `n + 1 - Math.log(Math.log2(mag)) / log2` — Math.log(Math.log2(mag))/log(2) = log2(log2|z|). Correct.

Also `rafPending` is unused; no problem.

Test in browser.

The fractal is displayed at the top but it's extremely small — it looks like it's only being rendered into the top ~80 pixels. In other words, H is being calculated as… wait, the fractal seems to be compressed at the top. This suggests the canvas's width/height attribute is fine, but in computeRow, y is being calculated by the H/W ratio… actually, the image looks like the entire fractal got compressed into the top 80px. This means the y0 calculation: scale = span/w, y0 = cy - (span*H/W)/2. If H were large… hmm, but the visible fractal only occupies the top 80px, with the rest being black (inside). Actually, is the black region the interior of the set? No — at span 3.4, points like (0.5, 2) should be outside and colored, not black.

Wait — maybe rendering only completed a few rows (8 rows × N chunks) and the screenshot captured mid-render? No, the status shows iters 256 and the fractal looks complete within the top strip. Actually, it's mid-render: chunk rows of 8 rows each via setTimeout… after 8 rows of dpr-scaled height (1600), it should show 8px of color. But the image shows a detailed full cardioid within the top 80px. That looks like the full fractal is rendered but the height is squashed — i.e., the y range is small. If H = 80*dpr… hmm.

Ah, I see: `canvas.width = W` where W = innerWidth*dpr. CSS size is 100vw. putImageData(0,0) is in device pixels. The fractal strip: at y0..y0+span*H/W, H/W = 800/1200, span*H/W = 2.27 complex units vertically, and the y range should be -1.135..1.135. The whole set is within im [-1,1]… actually the set's range is about [-1.3, 1.3] vertically? No: im range is about [-1.05, 1.05]? No! Vertically the Mandelbrot set's range is [-1,1]… actually, the set is roughly re [-2, 0.5], im [-1.25, 1.25]. At span 3.4, y0 = -1.135, y1 = 1.135. That means the entire set fits in the y range, and points above it (im > 1.135) don't exist. The visible region is im ∈ [-1.135, 1.135], and the set should appear centered and occupy most of the height.

But in the screenshot, the set is in the top 80px, occupying about 10% of the height. So it looks like the complex coordinates per pixel are much larger vertically… or is the screenshot viewport 1200×800 with the canvas only 1200×80? Wait, the image is a 1200×800 image with the fractal at the top.

Another explanation: the dpr is large, and putImageData is filling the entire device-pixel buffer, but… no.

Hmm, actually it might be mid-render with the screenshot taken after the first few chunks — but the detail suggests a completed small image. Let me think: chunk = 8 rows. If W*dpr… suppose dpr = 2, W=2400, H=1600. Rendering 8 rows per frame would take 200 frames → the screenshot should show 8px of color. The screenshot shows about 80px. Doesn't match.

What if H were actually small? H = floor(innerHeight * dpr). In the headless browser, innerHeight=800. Should be fine.

Wait — maybe the issue is: y0 = cy - (span*H/W)/2 with span*H/W = 3.4*(1600/2400)=2.267. Scale = span/w = 3.4/2400. Row 1600 → y is -1.133 to 1.133. Set's im max is about 1.04, so the set occupies most of the vertical direction. The cardioid's center is at im 0 → at canvas center (row 800, i.e. 400 css px). In the screenshot the set is at the top. So it doesn't match.

Unless the screenshot was taken mid-render and the top strip that's displayed… is that the region with im near the top? The top strip is im ∈ [1.133, ~1.0]… no wait, is row 0 the top? y0 = cy - (span*H/W)/2 = -1.133 at row 0 (top). So the top row is im = -1.133, the bottom is im = +1.133. The top of the screen should be im -1.133 (below the set, almost entirely outside, colored, not black). But in the screenshot, the top is colored and the bottom is black. And the visible "small" fractal…

The strip in the screenshot: colorful gradient at the top, then the set. The set appears at im around 0. If the top strip spans im ∈ [-1.133, x], then the set at im≈-0.5..0.5… the strip shows the tip of the cardioid pointing right, and… honestly it looks like a zoomed-in top portion.

A simpler hypothesis: rendering is in progress and the screenshot caught a partial state: the first ~80 css rows (160 device rows = 20 chunks) have been rendered. Row 0 is im = -1.133… that region should be a plain gradient without the set. But in the strip I see the whole cardioid shape!

Hmm wait, what if I'm wrong about the vertical flip: y increases upward on screen? y0 at row 0 is the minimum im (bottom of the set) but is drawn at the top of the screen. The region im ∈ [-1.133, ...] contains the bottom of the set. The strip shows what looks like the bottom of the cardioid and the top… hard to tell.

Actually, what if the screenshot just caught a very early partial render: only the first chunk… but a fully detailed cardioid is shown in 80px. At span 3.4 across 1200px, the cardioid should be about 300px wide. In the strip, the cardioid is small (about 90px wide) — that means in that strip the span per pixel is about 12x larger vertically than the expected 3.4/800…

Wait. I think the problem is: the H and W of the `image` ImageData. In resize, W = innerWidth*dpr. In computeRow, scale = span/w (w = W device px). y0 = cy - (span*H/W)/2 — H/W is correct. Hmm.

Let me just debug: check canvas.width/height and innerWidth etc. via browser inspect. Actually, the simplest is: maybe the headless viewport is 1200×800 with dpr=1, and the screenshot shows mid-render after the first ~80 rows… no, the detail doesn't match.

Another possibility: the screenshot tool captures the full 1200×800, and the canvas is actually only about 80px tall?? Because of `#fractal { width:100vw; height:100vh }` — that's fine. Hmm.

Let me look at the strip again: at the top there's a smooth gradient (cyan→green→yellow→orange→magenta→cyan), and in the center I see a thin cardioid+lobes shape. The gradient looks like a horizontal band — that's the appearance near the edge of the set? No.

Ah, wait. I've got it: the initial view might be zoomed in differently. INITIAL.span = 3.4, W=1200, H=800. The image should show the cardioid centered horizontally around re=-0.6… the set's re range is [-2, 0.47]. x0 = cx - span/2 = -0.6-1.7 = -2.3. So re goes from -2.3 to 1.1. The set's center -0.6 is at screen x = (−0.6 −(−2.3))/3.4 *1200 = 1.7/3.4*1200 = 600. Center ✓. Vertically, im 0 is at 400.

In the screenshot the set is horizontally centered (x≈795… actually slightly right of 795?). The cardioid in the screenshot is around x 730-860, center about 795. Hmm, not 600.

I'm confused. Anyway, let me investigate the canvas dimensions in the DOM.

With this, the full render completed and looks correct—the first screenshot was mid-render. The main cardioid + the circular lobe are fully visible.

Next, test wheel-based zoom at the cursor position, panning via drag, and reset. Wheel: use the browser's "key"? Browser tools support actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. There's "scroll"—probably it dispatches wheel events. Let me try scrolling at the position (795, 400) (cursor near the cardioid boundary) with negative delta.

Zooming worked: ×1.568, iterations increased to 755, zoomed in toward the cursor position (the top-right corner of the old view is displayed at the top-right corner of the screen, and the new center is at a complex point near the cursor position). The top strip is showing a new partial render (the new job has started rendering rows from the top down, and the old image remains until each row is updated — actually, since we're rendering rows top-to-bottom and putting the whole image, the old content stays below that). This is fine and responsive.

Let's wait and then take a screenshot to confirm completion.

Zoom worked correctly: the point that was at (795,400) — the cardioid/lobe junction — is still near the center of the screen (the small disk at around (700,615) is the period-2 lobe, and the junction is at around (790,560), near the cursor position). The iterations increased up to 755, and the new details were rendered. Zoom centering is maintained.

To confirm that additional details appear at the boundary, let's zoom in a few more times near that boundary point (790,560).

×2.858, iteration count 1419 — the zoom continues to follow the cursor. Wait, but the boundary point should be at (790,560)... the cardioid junction (where the main cardioid meets the period-2 bulb) is around (930,585)? Hmm, in this view the boundary between the large cardioid (right) and the period-2 bulb is at around (940,570). I zoomed at (790,560), which was on the boundary of the "spiral/antenna" near the upper cardioid. The point that was at (790,560) is... in the previous screenshot, (790,560) was near the upper-right boundary of the cardioid. Now in the new view, around (790,560) is still the curved boundary. Good enough — the anchor point is maintained.

Let me wait for rendering to complete, then test panning via drag.

The zoom was applied at the (790,560) position, which apparently was not on the cardioid boundary but on the outer "spiral antenna" region (the zoomed-in view is showing the region between the antennas — mostly smooth gradient, with the boundary in the lower right). Wait a sec, in the previous screenshot (790,560) was the curved boundary of the cardioid... no wait, it actually was. Looking at the previous frame: the top of the cardioid was around (790,560)? Actually, (790,560) was on the boundary — you can see the zoomed-in "spiral" structure in the lower right. Hmm, this structure in the lower right looks like the region near the spiral at -1.75+0.75i (the "Seahorse Valley" area). So it seems the zoom went too far. Anyway, the anchor point was maintained — the boundary is now near the lower-right corner (1100,730)... no wait, it should be near (790,560).

Hmm. In the new render, the fractal boundary appears in the lower-right region around (1150,750). That doesn't match (790,560). But wait — could this screenshot be mid-render? No, the whole screen is rendered.

Let me verify the calculation: after the first scroll, view = re -1.216, im -0.411, span = 3.4/1.568 = 2.168. Point at screen (790,560) (css px): scale = 2.168/1200 = 0.001807. x = -1.216 - 2.168/2 + 790*0.001807 = -2.299999… computing: -1.216-1.084 = -2.3 + 1.4275 = -0.8725. y: span*H/W = 2.168*800/1200 = 1.4453; y0 = -0.411 - 0.7227 = -1.1337; y = -1.1337 + 560*0.001807 = -1.1337+1.0119 = -0.1218.

After the second zoom: ×2.858, span = 3.4/2.858 = 1.1897, center re -1.7051, im -0.7367. Where is the point (-0.8725, -0.1218) on screen? scale = 1.1897/1200 = 0.0009914. x = (-0.8725 - (-1.7051 - 1.1897/2))/scale = (-0.8725 - (-2.30))/0.0009914 = 1.4275/0.0009914 = 1440. Outside the right edge of the screen! y: span*H/W = 0.7931; y0 = -0.7367-0.3966 = -1.1333; y = (-0.1218 - (-1.1333))/0.0009914 = 1.0115/0.0009914 = 1020. Outside the bottom edge of the screen!

So the anchor point is at (1440, 1020) — outside the 1200×800 viewport. The zoom was not centered on the cursor!

But wait — in the first scroll it looked correct. Let me check the first scroll: initial span 3.4, center (-0.6, 0). Cursor (795,400): scale=0.002833; x = -0.6-1.7+795*0.002833 = -2.3+2.2523 = -0.0477. y0 = -3.4*800/1200/2 = -1.1333; y = -1.1333+400*0.002833 = 0.

After: span = 3.4/1.568 = 2.168, center (-1.216, -0.4107). Where is (-0.0477, 0)? x = (-0.0477 - (-1.216-1.084))/scale, scale=2.168/1200=0.0018067. -1.216-1.084 = -2.2999… no, the half span is 1.084, so x0 = -1.216-1.084 = -2.3. x = (-0.0477+2.3)/0.0018067 = 2.2523/0.0018067 = 1246. This also slightly exceeds 1200!

Hmm, so in the zoomAt calculation:

view.cx = p.x - (sx * scale - newSpan / 2);
view.cy = p.y - (sy * scale - (newSpan * H / W) / 2);

Let me verify: the screen→complex conversion is x = cx - span/2 + sx*scale. We want p.x = newcx - newspan/2 + sx*newscale → newcx = p.x + newspan/2 - sx*newscale. I wrote view.cx = p.x - (sx*scale - newSpan/2) = p.x - sx*scale + newSpan/2. This is correct.

y: y = cy - (span*H/W)/2 + sy*scale → newcy = p.y + (newscale*H'/W)/2… wait, the y range: the vertical span of the image = newSpan * H / W (H/W is the aspect ratio). y = newcy - (newSpan*H/W)/2 + sy*newScale → newcy = p.y + (newSpan*H/W)/2 - sy*newScale. I wrote view.cy = p.y - (sy*scale - (newSpan * H / W) / 2) = same. Correct.

So the math is correct. Then why did my check give an out-of-screen result? Because the first screenshot I used for the anchor was actually… wait, I scrolled twice. In the first scroll, x=795, y=400, delta=-300 → factor = exp(450*0.0015) = exp(0.675) = 1.964. But the displayed zoom = ×1.568. exp(0.675) = 1.964 ≠ 1.568. Hmm, maybe the browser tool's scroll dispatches the wheel multiple times or the delta is different. If factor = 1.568, then exp(d*0.0015)=1.568 → d = ln(1.568)/0.0015 = 309. OK, maybe deltaY was 300 → 1.568? exp(0.45)=1.568. Yes! deltaY = -300 → factor = exp(300*0.0015) = exp(0.45) = 1.568 ✓. So a single wheel event with deltaY -300… wait, the factor is on the zoom side: zoom = INITIAL.span/view.span = 1/1.568? No: view.span = 3.4/1.568 = 2.168, which is a 1.568x zoom. factor = view.span_new = span*factor, factor = exp(-300*0.0015) = exp(-0.45) = 0.6376; span_new = 3.4*0.6376 = 2.168 ✓.

Then my check: in the new view, the point (-0.0477, 0) is at screen x = 1246. It should be at 795. So there's a bug. Let me recompute the anchor point more carefully.

Initial: cx=-0.6, cy=0, span=3.4, W=1200, H=800 (assuming dpr=1; the browser may have dpr=1).
sx=795, sy=400 (canvas rect is (0,0), dpr=1).
scale = 3.4/1200 = 0.0028333
p.x = -0.6 - 1.7 + 795*0.0028333 = -2.3 + 2.2525 = -0.0475
p.y = 0 - (3.4*800/1200)/2 + 400*0.0028333 = -1.13333 + 1.13333 = 0 ✓

zoomAt: newSpan = 3.4 * 0.6376 = 2.168 (clamp check: min span 1e-14, max INITIAL.span*4 = 13.6 — OK)
scale = 2.168/1200 = 0.00180667
view.cx = -0.0475 - (795*0.00180667 - 2.168/2) = -0.0475 - (1.4363 - 1.084) = -0.0475 - 0.3523 = -0.400
view.cy = 0 - (400*0.00180667 - (2.168*800/1200)/2) = -(0.72267 - 0.72267) = 0

But the displayed state is: re -1.216, im -0.4107! So view.cx became -1.216, not -0.40. A big difference. Which means the actual W (device pixels) differs from my assumption of 1200 (dpr>1?) or the rect offset differs, or the dpr scaling of e.clientX differs.

Suppose dpr=2, W=2400, H=1600. sx = 795*2 = 1590, sy=800.
Initial scale = 3.4/2400 = 0.00141667.
p.x = -2.3 + 1590*0.00141667 = -2.3+2.2525 = -0.0475 ✓ (same, good)
p.y = 0 - (3.4*1600/2400)/2 + 800*0.00141667 = -1.1333+1.1333 = 0 ✓
New scale = 2.168/2400.
view.cx = -0.0475 - (1590*0.00090333 - 1.084) = -0.0475 - (1.4363-1.084) = -0.400. Same. dpr-independent.

So view.cx should be -0.400, but the status is showing -1.216. There's definitely a bug. Difference: -1.216 - (-0.400) = -0.816. Hmm, -0.816 = ? -0.816 ≈ -(span*?). 0.816/0.00180667 = 451.6 px. Hmm.

Wait — maybe the scroll's x,y parameters specify the scroll position in some other way, and the browser tool scrolls in a different coordinate space, or the wheel event was dispatched with clientX/clientY = something else. Maybe the tool scrolls at the specified coordinates but in CSS px, and the page… or maybe the tool scrolls the *page* at that position (which is 0,0 since there's no scrollable page), and the clientX/Y of the dispatched event is (0,0) or (x/2)?

If the event had sx=0, sy=0 (top-left): view.cx = -0.0475 - (0 - 1.084) = 1.0365. Not -1.216.

If the event is at (397, 200) (half)? view.cx = -0.0475 - (397*0.00180667 - 1.084) = -0.0475 - (0.7173-1.084) = 0.299. No.

What sx would give -1.216? -1.216 = -0.0475 - (sx*0.00180667 - 1.084) → sx*0.00180667 = 0.0475 + 1.084 - 1.216… solving: (sx*scale - 1.084) = -0.0475+1.216 = 1.1685 → sx*scale = 2.2525 → sx = 1247. And for cy: -0.4107 = 0 - (sy*scale - 0.72267) → sy*scale = 1.1333 → sy = 627.4. So the effective event position ≈ (1247, 627) — this is exactly the position where the anchor point ended up in the second screenshot… hmm interesting. That would mean the wheel event's clientX/clientY was (1247, 627)??

Wait, maybe the browser tool's "scroll" scrolls the *content*, and the wheel event is dispatched at the element under (x,y) but the coordinates are relative… or maybe the tool scrolls at the center of the element? If the event is at the viewport center (600,400) with dpr… view.cx = -0.0475 - (600*0.00180667 - 1.084) = -0.0475 - 0.0 = -0.0475. No.

(1247,627) — that's the position where the anchor point ended up. Hmm, actually, did the tool dispatch the scroll at (x,y) in *device* pixels? If clientX/Y are CSS, no. If the tool dispatches the wheel with clientX = 1247, clientY = 627 for some reason… or the tool scrolls *from* the specified coordinates toward…

Actually, the browser tool's scroll might dispatch the wheel event at (x, y), and the y coordinate might be relative to the element's top… the canvas is at (0,0). Or the tool internally clamps x to the maximum scrollable region…

Anyway, let me check what the second scroll did. From the first view (-1.216, -0.4107, span 2.168), scroll with delta -400 at (790,560) → factor = exp(-0.6)=0.5488, newSpan = 1.1897. Reported center: (-1.7051, -0.7367).
If the event is at (790,560): p.x = -1.216-1.084+790*0.00180667 = -2.3+1.4273 = -0.8727; p.y = -0.4107-0.72267+560*0.00180667 = -1.13337+1.0117 = -0.12166.
Expected newcx = p.x + newspan/2 - sx*newscale = -0.8727 + 0.59485 - 790*0.00099142 = -0.2779+… computing: -0.8727+0.59485 = -0.27785; subtracting 0.78322 = -1.06107. Reported value: -1.7051. Difference -0.644. In scale units: 0.644/0.00099142 = 649 px → effective sx = 790+649 = 1439? Hmm, if the offset is consistent: effective event position = requested + (457, 67)? From the first: effective (1247,627) vs (795,400): offset (452, 227). Second: effective ≈ (1439, 627)? Let me solve for sy too: newcy = p.y + (newspan*H/W)/2 - sy*newscale = -0.12166 + 0.39656 - sy*0.00099142 = 0.2749 - sy*0.00099142 = -0.7367 → sy*0.00099142 = 1.0116 → sy = 1020. Offset = 1020-560 = 460. First offset: 627-400=227. Not consistent.

Hmm, wait, maybe the tool's scroll doesn't dispatch the wheel at (x,y) but instead scrolls a *page* region and clamps x,y to the *scrollable* content area… or maybe the tool scrolls at the element's center plus (x,y)? Element center (600,400) + (795,400) = (1395,800). No.

Or maybe the tool scrolls the iframe and the coordinates are relative to the document, and my canvas has a different rect in device pixels due to dpr. If dpr = 2, canvas CSS = 1200×800; but the tool's viewport might be 1200×800 CSS at dpr 2? My screenshot is a 1200×800 image. If dpr=1, no problem.

Let me test directly: dispatch a wheel event from the page? I can't run JS directly… the browser tools only have reload/inspect/screenshot/motion/click/drag/key/type/scroll. No evaluate. Hmm. But can I add debug info to the page? That's clunky.

Alternative: add a small debug overlay that records the clientX/clientY of the last wheel event and displays it in the status. This will let me see what the tool dispatches. Or just accept it: the centering behavior might just be off with respect to the tool's scroll simulation, but that's the tool's quirk, not a bug in the app. The first scroll's "the point stayed near the cursor" — actually, in the second screenshot, the point that was at (795,400) — the cardioid boundary junction — moved to (1247,627), off-screen. So centering at the cursor visibly failed *in this test*.

Wait, but actually — maybe the scroll tool scrolls at (x,y) but with y relative to the *bottom* of the viewport? First: sy_eff = 800-400 = 400? Then it should be correct, but no.

Let me add a debug display to check the actual event coordinates. Quick approach: append the last wheel event's clientX/clientY to the status text.

Wait a sec, I accidentally included a \r character in my edit... let me check what actually got written. The edit tool matched the oldText — but I used the \r escape. Let me display the file and see what happened.

Good, there are no \r characters, and the edit is clean. Add a `let debugWheel` declaration — it works without one (in a strict IIFE, does an implicit global assignment become an error? The IIFE is "use strict" → assigning to an undeclared variable inside a strict function throws a ReferenceError!). Needs to be declared.

Wait, the previous edit was using \r as a literal. Let me check the actual contents of the file around these edits — in the previous round, were the edits using \r escapes? Let me look at the file around line 291 and around currentJob.

Hmm — but did the second edit (let currentJob = null; let debugWheel) actually get applied? grep is only showing line 139 "let currentJob = null;" — let me verify.

However, `updateStatus` overwrites the statusEl.textContent — the debug info gets wiped out when rendering rows land (since updateStatus sets textContent anew). The debug text only exists between wheel and the next chunk. Let's make updateStatus include debugWheel:

I accidentally used `\r` in my edit, and it might have inserted a carriage return. Let me check the file around that line.

Alright, no carriage returns (grep -c returned nothing... no wait, the first grep with $'\r' didn't output any lines, so there are no CRs). Next, reload the browser and test scrolling.

In progress. Next, let's scroll at (795, 400) and check the debug coordinates.

The debug shows `wheel@0,0 ->0,0` — the browser tool's scroll action dispatches wheel events with clientX/clientY = 0,0 (it doesn't support the specified cursor position). In other words, the app's zoom was correctly centered on (0,0) (top-left), and the app's code is correct. The previous "anchor drift" was due to the tool's synthetic event position, not a bug.

The calculation is correct: when zooming at (0,0), the top-left point should stay fixed. In fact, in the first zoom the top-left corner remained as a smooth gradient... hard to verify visually, but the math has been verified earlier: for an event at (0,0), newcx = p.x + span/2 = -2.3 + 1.084 = -1.216 ✓ matches the status. Therefore, the cursor-centered zoom logic is correct.

Since the tool can't scroll at arbitrary points, I can verify cursor-centered zoom in another way: the calculation has been analytically verified, and the event coordinates pass through without issue. Good enough; I'll note in the report that wheel coordinates were only tested at (0,0) via the tool.

Also, the first screenshot after reload showed a partial mid-render (row-by-row) — that's fine.

Next, remove the debug output and test drag-to-pan and reset.

My edit call contained a weird \r escape—this was my mistake. Let me redo it with the exact plain text.

Hmm, the previous edit also had a \r escape sequence... but it's showing that 3 blocks were replaced. Wait, but the file doesn't contain \r (grep -c showed 0). So how did it match? Maybe the harness normalized it. Let me verify that the file is clean.

Debug has been removed, no CR. Next, I'll do a reload, verify pan via drag, and test reset.

Mid-render (chunked). Next, drag-pan: drag from (600,400) to (400,300).

Pan works: drag (600,400) → (400,300) moved the center from (-0.6, 0) to (-0.0333, 0.2833). Verify: dx = -200 css px → cx -= dx*scale = -(-200)*0.0028333 = +0.56667 → -0.6+0.5667 = -0.0333 ✓. dy = -100 → cy -= -100*0.0028333 = +0.28333 ✓. The direction is correct (dragging to the bottom-left moves the view to the top-right).

Next, test the reset view.

Hmm — the status is displayed as re -0.6, im 0, ×1.000 (the correct reset state), but the image is still showing the post-pan view! Wait — the image is showing the set shifted to the left... Actually, is this a mid-render state? No — the whole canvas is drawn, and it looks like the post-pan view (the set is offset to the right from center: the center of the cardioid is about 490, not 600... in fact, the cusp is cut off at the left edge, matching the state re=-0.033 of the post-pan view).

But the status says re -0.6. So it's possible that the reset triggered a render, but the screenshot captured the old pixels before the new job's rows landed? No — the job starts from row 0 (top), draws the top rows first, and puts the entire ImageData. Since the image buffer is shared, as the new rows compute, the top of the canvas updates and the bottom rows remain old. Screenshot: the top band (above y=60) looks different (dark), and the rest is old. So it's mid-render: after the click, only a few rows of the new job have been rendered (the top band is the start of the new image — the upper area with the magenta/dark coloring is the initial rows of the reset view).

Wait, but the status is already showing the reset value. updateStatus is called on each chunk. The click landed, and the render was in progress. Let me take another screenshot to confirm the final reset view.

The reset view matches the initial framing perfectly. Everything has been verified. Final check: the file is saved. Just confirm that the file exists and that it's the final version (debug has been removed). Done.

All verified. The final file has been saved to /tmp/job-bNe0q1/index.html. I'll report back.