Mandelbrot explorer · kimi-k3

Let me build the Mandelbrot explorer with chunked rendering to keep controls responsive. I'll write index.html with:
- Fullscreen canvas
- Smooth escape-time coloring (continuous iteration count), inside-set distinct color (black)
- Initial view showing main cardioid: real [-2.5, 1], imaginary centered
- Drag pan, wheel zoom to cursor
- Adaptive max iterations based on zoom
- Chunked rendering using requestAnimationFrame or setTimeout, render rows progressively
- Reset button
- preventDefault on wheel
- A crosshair/indicator maybe not needed

Let me write the code.

One issue: renderChunk draws via putImageData with dirty rect, but DPR — putImageData ignores CSS scaling, and canvas.width/height are device pixels, so that's fine. Let me test in the browser.

The render only filled the top ~160px, then stopped. The putImageData with dirty rect: `ctx.putImageData(img, 0, 0, 0, row, w, endRow - row)`. Wait — canvas is 1200x800 CSS, device pixel... DPR probably 1. Canvas height should be 800. Only first 160 rows filled — that suggests subsequent requestAnimationFrame chunks didn't run before the screenshot? Actually screenshot shows render appears stalled at 160 rows = 5 chunks of 32. Hmm, perhaps screenshot was taken early... but the render of 800 rows at 1200 wide with maxIter 200 shouldn't take that long. Maybe rAF chunks are running but putImageData with dirtyY row... The math: dirty rect (0, row, w, endRow-row) — correct.

Wait, the image shows the rendered strip only covers the top 160px but width is full. Maybe subsequent rAF calls aren't firing in the headless environment when idle? Let me wait and take another screenshot.

Full render completed fine — first screenshot was just taken mid-progressive-render. The initial view shows the main cardioid and lobes nicely.

Now test wheel zoom centered on cursor. The wheel action — the browser tool doesn't have a wheel action explicitly... Actions: reload, inspect, screenshot, motion, click, drag, key, type, scroll. "scroll" with delta probably maps to wheel. Let me hover at a boundary point, e.g., the seahorse valley around (740, 300)? Cursor point under zoom: pick a recognizable boundary point, e.g., the top of the period-2 bulb at around (520,290)? Let me scroll at the boundary between cardioid and bulb — around (620, 400)? Actually let's zoom at the seahorse valley: the neck between main cardioid and big bulb, around (620, 400). Negative delta = zoom in presumably (deltaY negative = zoom in). The scroll action takes delta. Let's scroll with negative delta at coordinates. Does scroll accept x/y? The tool schema has x, y, delta. Let me do several scrolls at the same point.

Hmm, the zoom happened (zoom 2.05×) but xmin didn't change — it stayed -2.6. The point under cursor should stay at cursor. Cursor at (620,400): fx = 620/1200 = 0.5167. cre = -2.6 + 0.5167*3.6 = -0.74. After zoom factor 0.487 (1.0015^-480 ≈ e^(-0.72) ≈ 0.487): xmin = cre + (-2.6 - cre)*0.487 = -0.74 + (-1.86)*0.487 = -1.646. But DOM shows xmin = -2.6, xmax=-0.847 — span 1.753, zoom 2.05×. That's as if fx=0... Actually xmin unchanged at -2.6 and xmax shrunk toward -0.847 — consistent with zoom anchored at xmin (fx=0). And ymin unchanged -0.9, ymax → -0.023. So it anchored at top-left, not the cursor!

Wait — did the screenshot image change? The image looks identical to the initial view, not zoomed. So maybe the screenshot is stale, or the render shows the same... The DOM says zoom 2.05× but the image shows full mandelbrot. Hmm, screenshot may have been captured before re-render? The image shows the same full view. Actually the image looks exactly the same as the previous one. The DOM info updated though.

Why anchored at top-left? e.clientX - rect.left... In the browser tool, scroll with x,y — maybe the synthesized wheel event had clientX=0? Possibly the scroll action ignores x/y and fires at (0,0). That would explain anchor at corner... But even corner anchor gives xmin=-2.6? If fx=0, cre = xmin = -2.6, so xmin stays -2.6. Yes! And cim = ymin = -0.9 stays. So the wheel event fired at client (0,0). The browser tool's scroll may not position the cursor.

Also image unchanged — perhaps the re-render hadn't been drawn yet at screenshot time, or the image is stale. Let me take a fresh screenshot.

The zoom re-rendered correctly (new view, detail of seahorse valley at bottom-right). Zoom math works; the tool's scroll just doesn't pass cursor coordinates (fired at 0,0). The zoom anchoring code is standard; anchored-at-cursor correctness is consistent with the code: with fx=0,fy=0 the corner stayed fixed, which is what we observed — xmin/ymin unchanged. That's actually evidence the anchoring math works: the point under the event's coordinates (0,0) stayed fixed.

Now test drag pan and Reset. Drag from (600,400) to (400,300), then screenshot, then click Reset and compare.

The bounds updated (re shifted by +0.292 ≈ 200px × (1.753/1200) = 0.292 ✓; im shifted by +0.146 ≈ 100px × (0.877/800) wait — imPerPx = (0.8766)/800 = 0.001096; dy = -100 → ymin -= dy*imPerPx = ymin + 0.1096. Actual: -0.9 → -0.7904, diff 0.1096 ✓). Pan math correct. Screenshot is stale again (shows old image) — the screenshot is taken before rAF redraw, it seems. Let me take another screenshot to confirm pan re-rendered, then click Reset.

Pan re-rendered correctly — view shifted, recomputed with fine detail. Now click Reset and verify framing matches initial.

Reset worked — bounds are exactly the initial ones (re [-2.6, 1.0], im [-1.2, 1.2] since canvas is 1200×800, aspect 2/3 → yhalf = 3.6*2/3/2 = 1.2 ✓; note the first DOM read earlier showed im [-0.9,0.9] because that was before resize? Actually initial load showed ±0.9 — that suggests at first render canvas.clientWidth/Height were different, then resize corrected. Anyway, now it's consistent). The screenshot is mid-render (top strip drawn). Take a final screenshot to confirm the reset framing matches initial.

Wait — the im range changed from [-0.9, 0.9] at load to [-1.2, 1.2] after reset. Why? At load: resetView() called before resize(), when canvas.width = 300, canvas.height = 150 (default), aspect = 0.5, yhalf = 3.6*0.5/2 = 0.9. Then resize() set canvas size and scheduleRender but did NOT reset the view — so the initial framing used a stale aspect ratio! The reset view after click uses canvas.width=1200 (with dpr 1), height 800, aspect 0.667 → ±1.2. Minor inconsistency: initial load framing vs reset framing differ. Fix: call resetView() on first resize when canvas size is first established. Simple: in resize, if it's the first call, resetView() before scheduleRender. Let me fix: add a flag `firstResize`.

Initial bounds now im [-1.2, 1.2] matching Reset. Screenshot is mid-render again (the tool captures immediately). Take one more screenshot to verify the full initial framing and that it matches the post-reset view.

The initial framing now shows the complete cardioid and lobes centered, matching the Reset view bounds. All checks pass. Console has only the sandbox warning (environment-related, not my code). Done — report.